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- Front Matter: Volume 10964
- The 10th International Conference on Information Optics and Photonics
Front Matter: Volume 10964
Front Matter: Volume 10964
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This PDF file contains the front matter associated with SPIE Proceedings Volume 10964, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.
The 10th International Conference on Information Optics and Photonics
Performance of active pulse shaping of high power multi-pass ring laser amplifier
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We demonstrated the arbitrary pulse shaping for a high power, joules class, and multi-pass ring Nd: glass laser amplifier system with nanosecond pulses based on the direct calculation method. While the square pulse with pulse energy 0.9mj and FWHM (full width at half maximum) pulse width 6ns, a 0.9J at 1Hz high power laser pulse energy is generated, which has the ability to change the waveform arbitrarily based on the full fiber front end. The laser amplifier system consists of three parts: full fiber seeder, diode pumped Nd: glass regenerative amplifier, and multi-pass ring amplifier. With the help of direct calculation method based on the input-output model, the input pulse shape has been calculated and the output pulse shape has been compared to the target pulse shape, showing that the simulation and experiment is consistent. Some other interesting pulse shapes have been produced with pre-compensated inject pulse based on the calculation which shows great potential to be applied in high power laser amplifier system with a desired pulse shape.
SnS2 nanosheets coated microfiber knot resonator for all-optical control of light functionality with fast response
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Optical fibers have long been the backbone of modern communication system. One way of extending the capability of optical fibers is to thin down the core sizes as microfiber which facilitates light-matter interaction through evanescent light. Among different microfiber based structure, the microfiber knot resonator (MKR) is a resonant structure which finds applications in lasing, filtering and optical switching [1-2]. Particularly, when the MKR structure is combined with functional two-dimensional materials, a large panel of devices can be achieved via the investigation of variations in resonance properties.
Here, a layered metal dichalcogenide semiconductor tin disulfide (SnS2), characterized with high intrinsic electron mobility and strong absorption in the visible light regime [3], is chosen to be coated onto MKR. The all-optical control of light functionality is demonstrated in MKR with SnS2 structure where the signal light power is controlled by the external violet pump power via the absorption property of SnS2. The device fabrication, characterization and obtained experimental results will be presented in the talk.
High speed large-field-of-view scanning microscopy imaging technology and system implementation
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In recent years, microscopic imaging technology is playing an increasingly important role in neurobiology, cell biology and microbiology. On the basis of high spatial resolution, if the field of view (FOV) is greatly improved and the time bandwidth is saved, microscopic imaging will play an important role in the research of the mechanism of neural circuit connection, increase imaging flux and provide the possibility for the digital storage of generous samples. Scanning imaging is now one of the major ways to increase FOV. However, the time bandwidth of traditional "walk-stop-shot" scanning mode is limited to the time-consuming signal transmission among the host computer, the host computer and the camera. This paper presents a microscopic imaging system for slice scanning by a distinctive "continuous scanning imaging mode", the camera exposures under continuous scanning motion. Based on FPGA, the location is obtained from the real-time decoding of the gratings signal, and the TTL signal controlling the camera is generated by the position comparator. And, 1) a pre-calibration strategy is adopted to ensure each sub FOV is within the depth of field, 2) a PID control algorithm based on piecewise interpolation is proposed to optimize the motion performance of the sample platform, 3) a fast iterative image restoration algorithm based on maximum a posteriori estimation is established to remove motion blur from a single image under high speed scanning motion. Finally, a 20mm x 15mm FOV (21722 x 17474 pixels) is scanned under the 20 times high NA objective lens less than 60s.
Determination of the characteristic wavelengths of photoacoustic glucose signals based on interval partial least square algorithm
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Glucose detection by means of the photoacoustic spectroscopy was performed in this paper. A set of photoacoustic detection system of glucose based on pulsed laser induced ultrasonic detection was established. Based on the photoacoustic system, a series of photoacoustic detection experiments for glucoses with different concentrations were performed. The time-resolved photoacoustic signals and photoacoustic peak-to-peak values of glucose under the excitation wavelengths of pulsed laser from 1300nm-2300nm were obtained. In order to get the optimal absorption wavelengths of glucose, the difference spectrum of photoacoustic peak-to-peak values between the glucoses and the pure water were used. At the same time, the interval partial least square algorithm was used to get the optimal absorption wavelength regions. The integrated wavelength region was divided into 10-15 sub-regions. For each sub-region, the model of partial least square was established, and the cross-validation method was also used. Results show that the wavelength regions of 1350-1440nm and 1490-1550nm are the optimal characteristic wavelength region. The prediction models were established in the optimal wavelength regions, four components of the partial least square algorithm were used. In the chosen optimal wavelengths, the correction coefficient between the glucose predicted concentration and original concentration can reach 0.9879 and 0.9969, respectively, the root mean square error of cross validations (RMSECV) are about 12.5mg/dl and 6.2mg/dl, respectively, the concentration bias is about 0.0581mg/dl, and 2.09mg/dl, respectively.
Reliability and manufacturability of 850 nm 50 Gbit/s PAM-4 vertical-cavity surface-emitting lasers
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Reliability and characterization of 850 nm 50 Gbit/s PAM-4 vertical-cavity surface-emitting lasers (VCSELs) are presented. These VCSELs have demonstrated a threshold current of 0.8 mA and a slope efficiency of 0.95 W/A. The maximum optical output power of 9 mW is achieved at a thermal rollover current of 13.5 mA. The optical power is up to 5 mW and the -3dB bandwidth is in excess of 17 GHz at 25°C and 6 mA bias. The current density and power dissipation density are low to 15 kA/cm2 and 25.5 kJ/cm2 , respectively. The standard deviations of photoluminescence peak wavelength and Fabry-Perot cavity wavelength of epitaxial wafer are 0.75 nm and 2.2 nm, respectively. After 1500 h of the reliability study no degradation or failures of the 22 VCSELs are observed at 80°C in a heating chamber at a bias of 6 mA. Considering high optical absorption of DX center, the impurity doping concentration of 3 pairs of N-DBRs that were adjacent to active region are optimized. The additional SiO2 passivation layer not only can provide moisture resistance but also provide a photon lifetime tuning. The output power increases by optimizing thickness of SiO2 layer reducing power dissipation density. Single thin oxide aperture is employed by slowing down the oxidizing rate and improving temperature during a VCSEL oxidation process to thereby reduce stress concentration of an oxidation. Single thin oxide aperture may limit the -3dB bandwidth, but the modulation characteristics can be improved by adopting advanced modulation techniques such as 4-level pulse amplitude modulation (PAM-4).
Experimental investigations of quality trapezoidal shape PMMA microchannel prepared by CO2 laser
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CO2 lasers often produce PMMA microchannels, as non-metallic materials have a strong absorption capability for mid and far infrared. Triangular cross-section microchannels have been fabricated by conventional methods, due to the Gaussian distribution of laser intensity. It cannot meet the requirements of microfluidic chips sometimes. In this paper, a multi-pass translational method is proposed, which based on the lateral heat-affected zone (HAZ) formed by single ablation, and multiple ablation with its width. This way not only produces a clean bottom like the static multi-pass method, but can modify the cross-sectional topography to produce a clean trapezoidal microchannel. Next, we evaluated the topography of microchannel by introducing the parameter "S", analyzing the variations in surface roughness and HAZ. All these indicate that the multi-pass translational method is a rapid and economic way of fabricating high quality trapezoidal microchannel on PMMA-based microfluidic devices.
Discussion and analysis on alignment error model of laser communication
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The influence of the alignment error in laser communication is analyzed. The link energy model with the position deviation at the image surface is established, and on the basis of this model, the spot deviation and the receiving optical axis deviation caused by the angular deviation of the optical axis are discussed and analyzed. Under the conditions of initial transceiver parameters, the link energy and the allowable maximum angle deviation with the distance of 0~2km are further calculated. The model formula of alignment error can be applied to analysis and discussion under the father distance. It has a theoretical guiding significance for the field laser communication test.
Upconversion of communication band light carrying orbital angular momentum using quasi-phase-matching
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The upconversion of an orbital angular momentum (OAM) carried light in communication band is preferable for building OAM-based upconversion optical communication networks. Here we experimentally study the behavior of OAM of communication band light in sum frequency generation process. The wavelength of the pump beam with sub-nanosecond pumping fields is 1064 nm and the communication band light is 1560 nm. Both beams are imprinted with OAM using vortex phase plates.The topological charges of the upconversion pulses at 632.5 nm are observed by a self-referenced interferometric technique. The OAM conserves in coupled nonlinear optical conversions is confirmed by counting the fringes in the interference intensity profile.The sum frequency generation is performed by using a periodically poled MgO-doped lithium niobate (PPLN) crystal under quasi-phase-matching conditions. We also gave analytical expressions for the upconversion of two OAM-carrying beams. The experimental results are well matched with the theoretical simulations.
The investigation for the influence of the line-width of probe light on the phase noise of phase-sensitive optical time domain reflectometry
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In this papers, the influence of the line-width of probe light on the phase noise of phase extracted based phase-sensitive optical time domain reflectometry (Φ-OTDR) is theoretical analyzed and experimentally investigated. Analysis indicates that broad line-width probe light suffers time varying wavelength drift and high level of laser phase noise, and thus guarantees high level phase noise of the Φ-OTDR. In distributed acoustic sensing along 500 m sensing fiber, the phase noise is evaluated for probe lights of different line-widths, and experimental results display that the phase noise increases as the line-width of probe light broadens.
Multimode-fiber/scattering-medium computational optical endoscopic imaging based on digital wavefront modulation
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Light wave becomes extremely distorted when it passes through a turbid medium. Indeed, the inhomogeneity of scattering medium and the mode dispersion of multimode optical fiber (MMF) always distort the propagation of light waves since they divert the propagation direction and disorder the spatial relationship of rays from the object. This becomes a big challenge for the applications of biological tissues endoscopic imaging. To overcome this problem, many methods based on computational optical imaging schemes have been reported and such a research has become a hot topic in recent years. These methods include the computational ghost imaging, the digital phase conjugation, the speckle correlation, the wavefront shaping, and the optical transmission matrix, etc. In this paper, we report our recent works on computational optical imaging based on digital wavefront modulation, which might be useful for the applications of endoscopy. On one hand, we propose a round-trip imaging method based on the optical transmission matrix of scattering medium, where the light wave is distorted twice. The object is recovered directly from the distorted output wave, while no scanning is required during the imaging process; one the other hand, by modulating the amplitude instead of the phase of the incident light wavefront, we propose a high-speed binary amplitude-only modulation method to focus and scan light through an MMF based on the digital micro-mirror device (DMD). This method can also be extended to focus and scan light at multiple planes along the axial direction by just modifying the input wavefront accordingly.
Tunable hybird optical filter based on a passive cavity for femtosecond lasers
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Utilizing the mechanism of cavity secondary resonance, we proposed a tunable hybrid optical filter combined band-pass spectral and low-pass noise filtering for femtosecond lasers. The experimental results shown that, by stabilizing the cavity length to different transmission peaks, the 3 dB bandwidths of the spectral filter can be tuned from 1.78 nm to 2.8 nm and the tunable cut-off frequency of the low-pass noise filter can be identified by their different attenuations which vary from 9.5 dB to 15.2 dB, of the relaxation oscillation in the laser relative intensity noise (RIN).
Experimental study on protection performance of the plasma array against the NEMP
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Strong electromagnetic pulse (EMP) may lead to serious damage once it is coupled into the interior of the electronic system. As a kind of special electromagnetic medium, plasma has the ability of shielding strong EMP. Therefore, EMP protection technology based on the plasma is of pratical significance. The experimental setup of the interaction between the nuclear electromagnetic pulse (NEMP) and the plasma based on a one-layer cylindrical plasma array is built. Combined with the density distribution characteristics, the protection performance of the plasma array against the NEMP is studied. The results indicate that the protection performance of the plasma array against the TE polarization NEMP is better than that against the TM one. For both TE and TM polarization NEMP, the one-layer cylindrical plasma array can reduce the transmission pulse energy greatly and the energy attenuation is up to 10dB when the electron density is 8.5×1016 m-3.
Theoretical research on new photoelectric mixing technology based on electro-optical modulation
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For the current photoelectric mixing technology, there are many problems such as small array size, high noise level and poor receiving stability. Combined with the idea of microwave photonic down-conversion technology, this paper proposes a new photoelectric mixing technology based on electro-optical modulation. Using high-resolution, low-cost, mature 2D sensors and electro-optical modulators to perform mixed-frequency demodulation at the optical level, not only overcomes the limitations of array size on image resolution, but also has the advantages of high energy utilization and high signal-to-noise ratio. A mathematics model was set up with the mixing efficiency and mixing signal-to-noise ratio as the key performance parameters. The influence of the operating point offset, modulation depth, and incident optical power on the performance parameters was analyzed. The results show that taking into account the mixing efficiency, IF signal amplitude and mixing signal-to-noise ratio, the electro-optic modulator works best when the modulation depth is at the maximum at the standard operating point, which are laying a theoretical foundation for the further research.
Fast OMP reconstruction for compressive hyperspectral imaging using joint spatial-spectral sparsity model
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Hyperspectral imaging typically produces huge data volume that demands enormous computational resources in terms of storage, computation and transmission, particularly when real-time processing is desired. In this paper, we study a lowcomplexity scheme for hyperspectral imaging completely bypassing high-complexity compression task. In this scheme, compressive hyperspectral data are acquired directly by a device similar to the single-pixel camera based on the principle of compressive sensing (CS). To decode the compressive data, we propose a flexible recovery strategy by taking advantage of the joint spatial-spectral correlation model of hyperspectral images. Moreover, a thorough investigation is analytically conducted on compressive hyperspectral data and we find that the compressive data still have strong spectral correlation. To make the recovery more accurate, an adaptive spectral band reordering algorithm is directly added to the compressive data before the reconstruction by making best use of spectral correlation. The real hyperspectral images are tested to demonstrate the feasibility and efficiency of the proposed algorithm. Experimental results indicate that the proposed recover algorithm can speed up the reconstruction process with reliable recovery quality.
Influence of multistage diffraction of grating on imaging quality of a dispersion-compensated polarization Sagnac interferometer
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The output beams of a dispersion-compensated polarization Sagnac interferometer include not only ±1st-order beams but also beams of 0th and other orders. Consequently, the contrast of the interference fringes generated in a focal plane array (FPA) is reduced, which means the quality of the image and reconstructed polarization images is poor. In this study, multistage diffraction is investigated to determine the effect of non-ideal beams on imaging quality. After determining the beams that can cast onto the FPA, the intensity on the FPA is studied with consideration of multistage diffraction. Results show that the non-ideal beams can lead to a serious reduction in imaging quality. The experiment and simulation results indicate that the beams can reduce the ratio of the fringe amplitude to the background signal to 1/8 from the ideal 1/2. Therefore, methods that can attenuate or eliminate other diffracted beams should be adopted. This conclusion is applicable to other optical structures containing gratings, such as a spatial heterodyne spectrometer.
20.38MHz all polarization maintaining figure-of-8 erbium-doped fiber laser based on nonlinear amplifying loop mirror
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We demonstrate a mode-locked all-polarization-maintaining figure-of-8 erbium-doped fiber laser, with a repetition rate of 20.38 MHz. The self-starting fiber laser is based on a structure of nonlinear amplifying loop mirror (NALM). The output pulse duration of this laser can be de-chirped to about 590 fs. Such all-fiber laser with a high repetition rate has the advantages of high stability and self-starting, which leads to many scientific applications.
Nonuniform fringe characteristics of cascaded symmetrically chirped long-period fiber gratings
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A novel scheme of cascaded symmetrically chirped long-period fiber gratings (CSCLPFG) is proposed in this paper. Two linearly chirped long-period fiber gratings with opposite chirp coefficients are concatenated without an in-between fiber. In this fiber Mach-Zehnder interferencer (MZI) configuration, the light of different wavelength experiences different propagation distance both in core and cladding due to the symmetrically chirped grating structure. As a result, the phase difference between core and cladding mode increases nonlinearly with wavelength, which gives rise to an increment of fringe spacing with wavelength and thus, a nonuniform fringe pattern in transmission spectrum. The fringe spacing increases with the decreasing slope of phase difference curve versus wavelength. A Fourier transform analysis of the nonuniform fringe shows that the frequency range is substantially enlarged by symmetrically chirping, as compared to the uniform fringe of the cascaded identically chirped gratings. The overall fringe frequency increases with the grating length, while the wavelength scope of the fringe envelope is dependent on both the length and the chirp. In addition, the fringe frequency can be further adjusted by inserting a separation fiber in between two gratings. The mode coupling mechanism and fringe characteristics are numerically investigated, which may provide a theoretical foundation for the potential applications of this fiber device in filtering and sensing areas.
Polarization changes of beams travelling through anisotropic turbulence for optics transmission
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Based on the extended Huygens-Fresnel principle and the unified theory of polarization and coherence, the explicit expression of cross-spectral density matrix for partially coherent beams in far field is derived. Also, we investigate the polarization changes of beams travelling through anisotropic turbulence along the horizontal link when the source is isotropic and anisotropic in correlation. Simulation results show strong relevance between the polarization states of beams and the source correlation. The conditions for partially coherent beams to be less affected by turbulence are given.
Study on the influence of scanning strategy on the morphology of laser micro-dimple texturing
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Laser surface texturing is an advanced technology which can effectively improve surface tribological properties and has been attracted wide attention. However, the large diameter micro-dimple cannot be finished by fixed-point pulse processing, and fewer researches about the effect of laser scanning strategy on large diameter micro-dimple texture have been reported. Therefore, the effect of laser scanning strategy on the morphology of large diameter micro-dimple texturing is discussed in this work. An experiment of micro-dimple texturing on the 40Cr steel temples is performed by using a nanosecond laser. The effect of laser scanning mode on the micro-dimple texture is investigated to determine a reasonable laser scanning mode. Meanwhile, the influence of scanning interval on the micro-dimple texture with different diameters is studied under the best scanning mode. Results show that the diameter of the micro-dimples which are processed by the fixed-point pulse is about 48.1μm, and the spiral scanning is the best scanning mode for the large diameter micro-dimple texture. For spiral scanning, with the increase of scanning interval, the diameter of micro-dimples increases slightly, while the depth of micro-dimples, the height and the width of craters decreases. In order to ensure that the micro-dimple texture has good formability, the scanning interval can be properly floated on the basis of 10μm, but the scanning interval should not be close to the diameter of micro-dimples processed by the fixed-point pulse.
Scale adaptive correlation filter tracking based on the autocorrelation matrix
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Target tracking is an important research in computer vision. It has wide applications in human-computer interaction, machine recognition and artificial intelligence. But most existing tracking methods can not calculate the target scale well, resulting in low tracking accuracy. Some scale adaptive algorithms calculate scale by multiple attempts, which greatly improves the computational complexity. For this problem, this paper proposed a new scale adaptive correlation filter tracking algorithm based on the autocorrelation matrix. The method is based on the circulant structure of tracking-bydetection with kernels(CSK). Firstly, the sample of each frame is constructed as a cyclic matrix, and the kernel recursive least square (KRLS) method is used to learn the classifier. FFT accelerates the convolution process and makes the tracking speed faster. Finally, calculate the autocorrelation matrix using the standard image of each frame during correlation filtering. And get the target scale through the mapping of features between autocorrelation matrix. The experimental results showed that our method can update target scale during real-time tracking and improve the tracking accuracy effectively. Comparing to other algorithms, our algorithm can quickly adapt target scale during tracking and perform better in accuracy and speed.
Analysis of three dimensional recovery algorithms’ influence on the ranging accuracy of Gm-APD Ladar
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Geiger-mode Avalanche Photo Diode(Gm-APD) Ladar is a probabilistic device outputting three dimensional(3D) images based on the multi-frame imaging statistics, which makes the 3D recovery algorithm one of the key techniques of imaging system. Besides, performance of algorithm plays a crucial role in improving recovery quality of 3D images. This paper researches three 3D algorithms based on histograms, containing peak-selecting algorithm, range-selecting algorithm and Gaussian fitting algorithm. Firstly, the triggered model of Gm-APD is analyzed based on the work timing sequence and imaging theory of Gm-APD Ladar. Meanwhile, the recovery principles of three algorithms are analyzed and clarified. Secondly, two evaluation criterions, average range error and accuracy of range recovery, are raised to evaluate range accuracy. Finally, range images are obtained with above three algorithms in statistics of different frames, based on original data obtained from 64 × 64 Gm-APD Ladar imaging experiment. With the three construction algorithms, the result shows that the range accuracy of recovery range images improves and converges to 0.2~0.3m with the increment of number of frames participating in the statistics, and the accuracy of range recovery can be up to 90%. In low frame numbers, the range accuracy of recovery range profile is worst with peak-selecting algorithm, and the average range error with rangeselecting algorithm performs best while accuracy of range recovery with Gaussian fitting algorithm is highest among all algorithms. The result has important guiding significance for the choice of recovery algorithm under different requests.
Quantitative phase imaging using dual-channel Fresnel bi-prism interference microscope
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A new type of dual-channel interference microscope for quantitative phase imaging of transparent microscopic object is presented in this paper, which is comprised of an ordinary unpolarized cube beam-splitter and a ready-made Fresnel bi-prism. For this proposed microscope, the cube beam-splitter is tilted in an unconventional way, and the incident beam is only incident to one half of the cube beam-splitter and it is parallel with the central semi-reflecting layer of the cube beam-splitter. Subsequently, two copies of incident beam are created, the transmission beam is the simply replica and the reflection beam is the mirror-reverted replica. Behind the cube beam-splitter, the Fresnel bi-prism is placed in alignment with the cube beam-splitter and used to deflect the two generated beams to encounter and form the off-axis interference. Based on this kind of off-axis interference mode, we only need to record one interferogram for phase retrieval. Using this method, when the sample is only irradiated by one half of the incident beam, we can only use a single digital camera to record two symmetrical interference channels with a relative π (rad) phase-shift in one interferogram simultaneously. In addition, because of using less ordinary off-the-shelf optical elements, our method is simple and easy to operate with low cost, and it may be applied to traditional inverted optical microscope. Experimental results show that this method is suitable for quantitative phase imaging of transparent microscopic object.
Design of all solid large mode area and nearly zero flattened dispersion microstructure fiber
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By employing germanium up-doped and fluorine down-doped, a novel design of all solid trench-assisted 19-core fiber with nearly zero flattened dispersion, large mode area and single supermode transmission is proposed. Dispersion can be adjusted by combining mode coupling mechanism and low refractive index trench. By using this strategy, the a flattened dispersion of 5.28±0.52ps/(nm·km) within a wavelength range of 1430nm~1680nm, which covers whole S+C+L+U communication band and an effective mode area up to 288.2μm2 at 1.55μm are achieved simultaneously. The fiber we proposed here has all solid and structure which is easy to draw and applicable to current DWDM system.
QoS based optimization of multi-user selection with criterion of SLNR
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As a resolve to high complexity of user selection and different users with different requirements of QoS(Quality of Services) optimization of multi-user selection with criterion of SLNR based on QoS is proposed in this paper with maximization of SLNR(Signal-to-leakage and Noises Ratio) as standard and different settlements of scheduling for different kinds of users in MIMO (Multiple-input multiple-Output) system. The simulation compares this algorithm with round robin scheduling and leakage based user scheduling. The results show the proposed optimization is much better not only in channel capacity but also in throughput and BER (Bit error rate) than these two algorithms.
A fiber ring laser for temperature sensing based on in-fiber Mach-Zehnder interferometer
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In this paper, a novel fiber ring laser (FRL) is proposed and investigated based on modal interference. Through core-offset splicing technique, an in-fiber Mach-Zehnder interferometer (MZI) is fabricated based on thin-core fiber and single mode fibers. Its distribution of light filed is comprehensively analyzed by beam propagation method. The FRL is then setup, in which the fabricated MZI is used as a band-pass filter. The output of laser is controlled and optimized by accurately adjusting the state of polarization controller. The experimental results show that, the extinction ratio of lasing wavelength reaches 39.8 dB, and the line width is less than 0.1 nm. Moreover, the proposed FRL is applied in temperature sensing, and the tested sensitivity reaches 122.7 pm/°C with the linearity of 0.9982. In addition, by calculation, the amplitude noise and the spectrum resolution are 8.84×10-3 nm and 2.89×10-3 nm, respectively. Therefore the detection limit in this laser sensor is about 0.07°C, which is obviously higher than that in passive fiber optic sensor.
Characteristics of the calamine analyzed by terahertz time-domain technology
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The characteristics of Calamines has been firstly analyzed by terahertz time-domain spectroscopy. Results show that the main composition of the Calamine is calcite. And the terahertz absorption much relates with the particle size, sample thickness, as well as the proportion of polytetrafluorethylene mixed in the sample.
Characteristics of the lapis chloriti analyzed by the terahertz time-domain technology
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As a traditional mineral medicine, Lapis Chloriti has attracted much attentions in recent years. Based on the components determined by the X-ray diffraction, the Lapis Chloriti were characterized by the terahertz time domain spectroscopy. Results show that the absorption of sample has positive correlation with concentration. The more mass with Lapis Chloriti, the more absorption. And the absorption becomes more intense with the particle size increasing. In addition, the absorption influenced by other factors are also compared and discussed.
Cryogenic characteristics of in-fiber Mach-Zehnder interferometers based on EDF and MMF
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In-fiber modal interferometers have been widely used in the applications of biochemical sensing, mine safety and health monitoring of buildings. The temperature feature of sensors is one of the most important characteristics, but the studies are rarely reported under the condition of subzero temperature. In this paper, through core-mismatch fiber splicing method, three in-fiber Mach-Zehnder interferometers (MZIs) are fabricated based on single-mode fiber (SMF), erbium-doped fiber (EDF, with core diameter of 3.6 μm) and multimode fiber (MMF, with core diameter of 50 μm), respectively. Their interference patterns are investigated through beam propagation method and Fast Fourier Transform analysis. The comprehensive tests of temperature are then performed in the range from -40 to 0°C. The experimental results show that, in subzero temperature, the transmission spectrums of MZI sensors based on single mode fiber (SMF) and MMF are worsened in terms of fringe visibility and intensity. And the sensitivity of MMF-based structure is 68.8 pm/°C with a 12.3-dB deduction of fringe visibility. Comparatively, the EDF-based MZI presents ideal sensitivity due to negative gain-temperature feature. By calculation, the 124.7 pm/°C sensitivity is gained with the linearity of 0.9892. Moreover, 10-dB enhancement in intensity and over-20-dB fringe visibility are demonstrated, which indicates that the EDF-based sensor is potential and promising for the applications of cryogenic sensing.
Study on the phase of interference signal in phase extraction based phase-sensitive optical time domain reflectometry
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In a phase extraction based phase-sensitive optical time domain reflectometry (Φ-OTDR), external perturbation induced phase variation of Rayleigh backscattered light-wave (RBL) is obtained from time varying interference signal that is comprised of two RBLs with a spatial shift along the sensing fiber. In this paper, the phase of the interference signal in the phase extraction based Φ-OTDR is studied. Derivation is performed on the interference signal considering the interference of multiple RBL within probe pulse covered fiber section. Theoretical analysis and experimental results reveal that the phase of interference signal are wavelength independent while the intensity of interference signal are wavelength dependent.
Slow light via Stimulated Brillouin Scattering in few-mode fibers
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Intermodal Brillouin frequency shift and Brillouin gain spectrum in few-mode fibers are investigated by full vectorial finite element method, and the influences of pump power on the time delay and pulse broadening factor are also simulated. The simulation results show that Brillouin gain of intermodal stimulated Brillouin scattering varies with different modes pairs. Time delay increases with increasing of pump power. Pulse broadening factors decrease with the input signal pulse width but increase with the input pump power. Optimized results show that time delay of LP01 - LP01mode pair is 213.2ns, and the corresponding pulse broadening factors is 1.126.
Variable bit rate optical communication link between LEO satellite and ground station
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By rotating the half-wave plate, the variable communication bit rate between 5.12Gbps and 2.56Gbps has been verified at satellite-to-ground optical communication linkage, the communication link used Differential Phase Shift Keying(DPSK) modulation format and the wavelength is 1549.731nm. Without error correcting code and adaptive optics, an average bit error rate of 1.9E-9 was achieved while the link distance exceeded 1500km.
Recognition for multiple sources of bioluminescence tomography: a comparative study
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Bioluminescence tomography (BLT) can reconstruct internal bioluminescent source from the surface measurements. However, multiple sources resolving of BLT is always a challenge. In this work, a comparative study on hybrid clustering algorithm, synchronization-based clustering algorithm and iterative self-organizing data analysis technique algorithm for multiple sources recognition of BLT is conducted. Simulation experiments on two and three sources reconstruction are demonstrated the performances of these three algorithms. The results show that the iterative selforganizing data analysis technique is more suitable for the closer multiple-targets and the other two algorithms are suitable for distant targets. Moreover, iterative self-organizing data analysis technique has the least computing time.
Effect of magnetic field confinement on LIBS spectral enhancement and shape
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In order to enhance the emission spectrum of plasma in laser induced breakdown spectroscopy (LIBS), magnetic fields with different intensities were applied around the plasma to investigate its enhancement. Adjust the laser energy to 60mJ, change the magnetic field strength, use the traditional LIBS, magnetic field enhanced LIBS (MF-LIBS) for laser-induced breakdown of pure copper samples, to obtain the spectral comparison of characteristic line of trace elements (Bi I 206.16 nm) under different constraints and analysis of its enhancement mechanism. The experimental results show that the magnetic field of 153mT will reduce the spectral intensity, the 20mT, 50mT, and 90mT magnetic fields will enhance the spectral intensity. The stronger the magnetic field, the better the spectral enhancement effect, but the enhancement effect of 20mt is not obvious. The Lorenz fitting coefficient of the line is the lowest when magnetic field is not applied, the fitting coefficient gradually increases at 153mT, 20mT, 50mT and 90mT magnetic fields, indicating that the line shape is closer to the Lorentz type. And the spectral line width are also larger and reaches the largest when the 90 mT magnetic field is applied.
Maskless fabrication of multifocal microlens arrays on silica glass by multi-step laser-tunable wet etching method
Yan Ou,
Jinwen Qian,
Yifeng Xiao,
et al.
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This paper reports a simple method of creating multifocal microlens arrays on silica glass. The method involves the multi-step femtosecond-laser exposures followed by a chemical wet-etching process on silica glass, which enable fabrication of multi-layers concentric microstructures with high-quality and smooth curved surfaces. The flexibility of the maskless process was demonstrated in tuning the shape and depth of the multilayer concave structures by the arrangements of the laser exposure energy and chemical etching time. In addition, microlenses with different layers were fabricated and the results revealed their high surface quality and good optical property in creating multi-focus.
Ultra-wide and nearly flat-top gain spectrum in asymmetric quantum-well structure for InGaAs tunable lasers
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For tunable quantum well lasers, it has been a huge challenge all along how to achieve an ultra-wide tuning spectrum far exceeding the full width at half maximum (FWHM) of gain in a classic quantum well and the uniform power output for all tunable wavelengths of the laser under a fixed injection power, especially based on a single well structure. In this paper, we are reporting some amazing results from a special asymmetrical InGaAs quantum well structure, with which both incredibly extremely-wide and nearly uniform gain spectra are obtained with a fixed injection power. The excellent gain characteristics may make above dream come ture for the InGaAs-based tunable lasers. The formation of the structure is associated with the Indium-rich island effect. The analysis showed that the spectrally-tunable range from this special well structure could be up to 6 times as broad as the FWHM of gain in the classic InGaAs well and the gain spectrum with quasi-rectangular feature in transverse electric mode was obtained as well. It enables nearly identical power output over the total spectrally tunable range of the laser to be realized with a fixed optical injection power.
Silicon Mach-Zehnder modulator using a highly-efficient L-shape PN junction
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We demonstrate a silicon Mach-Zehnder modulator with L-shaped PN junctions to improve the modulation efficiency. The L-shape doping profile of the PN junction is obtained through multiple ion implantations with proper dose and energy. The depletion region of the PN junction has a strong overlap with the waveguide optical mode, resulting in improved modulation efficiency. We optimize the doping conditions to get a balanced performance in terms of modulator efficiency, insertion loss, and bandwidth. The measurement of the fabricated modulator reveals that the π phase shift voltage is 2.6 V for a 3-mm-long modulation arm. The modulation efficiency thus is Vπ·Lπ = 0.78 V·cm. The static extinction ratio is about 30 dB. The on-chip insertion loss is around 8.1 dB at zero bias. The EE 3-dB bandwidth is beyond 30 GHz at -2 V DC bias. Modulation of 32 Gb/s on-off keying (OOK) and binary phase-shift keying (BPSK) signals is successfully achieved.
Phase-shifting digital holography with vortex lens
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Phase-shifting digital holography (PSDH) is considered as a promising imaging technique with wide application in optical storage, topography measurement and defect detection. The amplitude-only vortex lens is a kind of diffractive optical elements (DOEs) which can be used for focusing and imaging in a wide spectral region, such as coherent X-rays and terahertz wave. Here four-step PSDH with an amplitude-only vortex lens is proposed. Four frames of hologram can be recorded by rotating the vortex lens installed in the reference beam path. Both a 1951 U.S. air force resolution test target and a vortex focal spot are measured by four-step PSDH with vortex lens. The experimental results are in good agreement with the theoretical analysis and verify the validity of our proposed PSDH with vortex lens.
Interoperation of 400GBASE-LR8 physical interfaces using CFP8 pluggable modules
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In this talk, we first review the current status for 400GBASE client-side optics standard and multi-source agreement (MSA). We then compare different form factors for 400GE modules, like CFP8, OSFP and QSFP-DD. The essential techniques to implement 400GE, like pulse amplitude modulation (PAM4), forward error correction (FEC) and continuous time-domain linear equalizer (CTLE), are discussed. A 400GE physical interface card (PIC) in Juniper’s PTX5000 platform has been developed, conforming to latest IEEE802.3bs standard. To validate the PIC’s performance, a commercial optical network tester (ONT) and the PIC are optically interconnected through two CFP8-LR8 modules. The CFP8-LR8 module utilizes 8 optical wavelengths through coarse wavelength division multiplexing (CWDM). Each wavelength carries 50Gb/s PAM4 signal. The signal transmits through 10km single mode fiber (SMF). The ONT generates framed 400GE signal and sends it to PIC through the first CFP8 module. The PIC recovers the signal, performs an internal loopback, and sends 400GE signal back to the ONT through the second CFP8 module. The optical spectrum, eye diagram, receiver sensitivity, long time soaking results, and internal digital diagnosis monitoring (DDM) result are fully characterized. The pre-FEC bit error rate (BER) is well below the KP4 FEC threshold of 2.2e-4. After KP4 FEC, error-free performance over 30km SMF is achieved. In this way, we demonstrate both the inter-operation between the PIC and the ONT, as well as the inter-operation between two CFP8 modules. This demonstration represents the successful implementation of 400GE interface in the core IP/MPLS router.
A new approach to generate the optical millimeter-wave signals using frequency 12-tupling without an optical filter
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In this work, we propose a novel approach to generate high-quality optical millimeter-wave signals using frequency 12-tupling without an optical filter. The proposed approach is comprised of one dual parallel Mach- Zehnder modulators. The two sub-MZMs, biased at the maximum optical transmission point, which is only used for even-order optical harmonic generation, and introduces a phase shift on the optical output signal between the sub- MZMs. By properly adjusting the MZM biasing point, RF LO voltages and phases shift, sixth order optical sidebands only are generated which can result in 12-tupled mm-wave at the photo detector. Optical sideband suppression ratio (OSSR) higher than 37.65 dB and radio frequency spurious sideband suppression ratio (RFSSR) not less than 32.08 dB are achieved in this scheme. The performance of the signal in terms of OSSR and RFSSR is discussed, and the effects of non-ideal factors on OSSR and RFSSR are analyzed.
Shell thickness dependent plasmonic resonances in concentric core-shell nanoparticles
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In this paper, we investigate the effects of silver shell thickness on the pasmonic resonances in single layer concentric core-shell particles by Mie theory. The plasmonic resonance is shown to be strongly influenced by the changing of shell thickness which leads the changes of dipolar and high order extinction resonance wavelength shift properties. Theoretical calculations indicated plasmon hybridization and phase retardation play an important role to influence the shift direction. Furthermore, different environment and geometrical properties are also considered.
All polarization-maintaining, figure-of-9 dispersion-managed Er: fiber laser
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In this paper, passively mode-locked all polarization-maintaining (PM) dispersion-managed erbium-doped figure-of-9 fiber oscillator based on a nonlinear amplifying loop mirror (NALM) is demonstrated. The figure-of-9 fiber laser can generate 25.7-nm chirped-pulse at a center wavelength of 1550 nm with a repetition of 46.6 MHz, a pulse energy of 0.2 nJ, and a chirped pulse width of 571 fs. The laser output is then amplified by pre-chirped managed nonlinear amplification setup to 5 nJ and further compressed down to 167 fs. Compared to previous studies, the laser presented here has advantages of all-fiber structure, no Kelly sideband and wider bandwidth.
High-Q in-plane channel drop filter based on two-dimensional photonic crystals for dense wavelength division multiplexing
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We proposed a high-Q in-plane channel drop filter using photonic crystal (PhC) cavities that are defined by an effective Aubry-André-Harper (AAH) bichromatic potential. The channel drop filter consists of AAH cavities and line-defect waveguides. Three-port structure with a wavelength-selective reflection cavity is applied. The parameters of the channel drop filter is analyzed by two-dimensional (2D) finite-difference-time-domain (FDTD) method. The simulation results are namely, the center wavelength of the filter being 1573.0 nm, and the insertion loss being smaller than 0.6 dB. The 3 dB bandwidth is 0.2 nm, and the loaded Q is up to 8×103. So the proposed device can be applied in a dense wavelength division multiplexing (DWDM) system with a 100 GHz channel spacing. Besides, the channel drop filter has a broad free spectral range (FSR) of around 250 nm, covering from 1350 nm to 1600 nm. The footprint of the channel drop filter unit is only 10 μm×20 μm.
Power coupling characteristics of a single mode optical fiber with a rectangular hole
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A single mode optical fiber with a rectangular hole is proposed. Power coupling characteristics of the optical fiber are analyzed and discussed using numerical method. Firstly, the coupling intensity from the fiber core to the rectangular hole is investigated in different distances between the fiber core and the rectangular hole and different refractive index of the rectangular hole. Secondly, the power complete conversion and transmission characteristics are also investigated in different distances between the fiber core and the rectangular hole and different refractive index of the rectangular hole. The results show that the coupling efficiency of the proposed optical fiber from the fiber core to the rectangular hole can nearly reach to 50%. The high coupling efficiency from the fiber core to the rectangular hole can be used to develop the high efficiency mode converters. Moreover, the results also show that the coupling efficiency is higher when the refractive index of the rectangular hole is bigger than the refractive index of the fiber core. So, the proposed optical fiber has the potential application value in high refractive index sensing.
Q-Switched Tm-doped fiber ring laser using Mo0.8W0.2S2 saturable absorber
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Mixed molybdenum tungsten disulphide (MoxW1-xS2), a new member of the transition metal dichalcogenides, has drawn much research attention in the photonic devices. In this work, we demonstrate a Q-switched Tm-doped fiber laser (TDF) using Mo0.8W0.2S2 polymer film as a saturable absorber (SA). Mo0.8W0.2S2 is obtained by microwave-assisted solvothermal method and its nanosheets are embedded into a polyvinyl alcohol (PVA) film. The film SA is sandwiched between two fiber connectors and is inserted into the all-fiber TDF laser cavity. The total cavity length of TDF is 30m and a 4 m Tmdoped fiber is used as the gain medium. The TDF is pumped by a multimode 793nm laser diode (LD). Use the polarization controller (PC) to change the polarization states, a relatively stable Q-switched pulse train are realized when the pump power up to 2.17 W. The output power of the oscillator increase from 4.4 mW to 7.3 mW with the pulse repetition rate from 11.9 kHz to 15.7 kHz. In addition, the shortest pulse duration of 11.7 μs generated with the pump power of 2.26W.
Research on surface plasmon resonance sensor based on wavelength and angular combined modulations
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To wavelength modulation SPR sensor, the measuring sensitivity of refractive index increases with wavelength. A broadband light source (700 nm~900 nm) with relative narrow bandwidth at long wavelength is selected, to measure the refractive index of surrounding medium by using SPR reflection power spectrums, in order to obtain relatively higher sensitivity and resolution. But the measuring range of refractive index is decreased by the reduction in bandwidth of light source. We propose a surface plasmon resonance sensor based on wavelength and angular combined modulations, in order to solve the mutual restriction of measuring range and sensitivity/ resolution, sectional measurement method is adopted, i.e. different incident angles are selected respectively, which will detect different measuring ranges of refractive index. Wavelength and angular combined SPR modulations can cover the whole measuring range of refractive index, and improve the measuring sensitivity and resolution simultaneously.
QoS evaluation method of optical network based on optical network alarm mega data
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Automatic evaluation of optical network service quality is a research hotspot in optical network operation and maintenance management. Based on the large alarm data of optical network, a evaluation method of optical network service quality based on FCM and rough set theory is proposed in this paper. First, the evaluation index is selected based on the classification statistics of alarm data; Secondly, adopt the FCM method to fuzzy clustering of raw data, and locate the fuzzy language item; Finally, extract the optical network service quality evaluation rule and establish system of the optical network service quality evaluation. The test shows that the accuracy of this method is 73% based on the 22 alarm samples in an optical network and the accuracy of the evaluation increases with the increase of the number of samples.
Polarization-controllable structure color based on the one-dimension stacked array with polarized absorption peaks
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It’s interesting that the artificial structure colors can be actively manipulated by external stimuli such as solvents, temperature, and mechanical force. In this paper, polarization state, the inherent characteristic of incident light, is used to control the structure color by a one-dimension metamaterial perfect absorber with polarized absorption peaks based on the stacked array. The nanostructure, consisting of two metal-dielectric pairs and a bottom metallic film, shows above 90% reflectivity from 652 nm to 750 nm (the red structure color) for TE and above 80% reflectivity from 584 nm to 635 nm (the orange structure color) for TM. Because our designed one-dimension absorber has the absorption peaks at 548 nm and 684 nm for TE and TM, respectively. So the polarization-controllable structure color gradually changes from red to orange when the polarization angles increase from 0° (TE) to 90° (TM). The underlying physical mechanisms of high absorptivity is explained by the electric and magnetic fields distribution.
Low loss negative curvature fiber with circular internally tangent nested tube in elliptical tubes
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In this paper, we propose the low loss negative curvature fiber with circular internally tangent nested tube in elliptical cladding tubes. The leakage loss can be decreased because the elliptical cladding tubes have higher curvature at the core boundary compared to the circular cladding tubes. The circular nested tube in the elliptical cladding tubes provides an additional antiresonant reflection element to reach lower leakage loss. The simulation results show the negative curvature hollow core fiber in this paper has a low leakage loss in the spectral region from 1.3μm to 1.7μm. In particular, the leakage loss is 0.012dB/km at 1.55μm.
Angular variation measurement of spheroids using defocused interferometric particle imaging
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The light scattering properties of a transparent spheroidal particle is investigated using defocused interferometric particle imaging. Based on optical transfer matrix theory, the out-of-focus images are simulated using Matlab. We found that the angular variation of a spheroidal particle exhibits isometric with angular variation of the speckle of out-of-focus image. The out-of-focus images of transparent spheroidal particles under different angle of rotation are experimentally acquired using interferometric particle imaging system. The experimental results showed agreement with the simulation results. Thus, we propose a method for obtaining the angular variation of a spheroidal particle using out-of-focus image.
Optical design of a refractometer with the liquid prism
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Here a refractometer with the liquid prism is proposed. It has a simple structure, low cost and a large measurable refractive index range. When the vertex angle of liquid prism is 30°, the measurable refractive index range is up to 1.00-3.86, while the common refractometers have only the measurable range of 1.30-1.70. The optical system of this refractometer is design, where the angle of field is 80° and the total length is 110mm. A linear array CCD is used as the image receiver. The design results show that MTF is 0.35 in the tangential surface and 0.55 in the sagittal surface at the Nyquist frequency of 70lp/mm and the full field. The MTF values of other fields are more than 0.6, and the maximum distortion is 0.37%.
Analysis of small vessel cochlear blood flow regulation during loud sound exposure in the mouse
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Using optical coherence tomography angiography, we measured blood flow from the vessels in the lateral wall in the mouse cochlea directly through bone in mice with and without sympathetic neuronal function. We present in vivo imaging of blood flow and mechanical vibration in mice subjected to 30 min of loud sound. Loud sound caused blood flow reduction. In mice with superior cervical ganglion ablation, the loud sound-induced reduction in blood flow was partially ameliorated. These results demonstrate that sympathetic innervation likely plays a role in the pathological decrease in blood flow observed in the lateral wall vessels in response to loud sound.
Electrically controlled liquid-crystal microlens arrays based on plane nonuniform spiral microcoils
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In this paper, a new type of electrically controlled liquid-crystal microlens arrays (ECLCMAs) based on plane nonuniform spiral microcoils (PNSMs) is proposed. The microlens array is based on a nematic liquid-crystal material, which presents a special characteristics of optical anisotropy and birefringence, and is fabricated by common ultraviolet lithography and dry ICP etching process to form needed PNSMs pattern. In the ECLCMAs, a glass substrate precoated by a film of indium tin oxide (ITO) on both surfaces of substrate is adopted. The key center electrode for shaping each functioned LC cell is drilled using a laser etching and emery polishing process. Metallic indium particles are selected to connect the upper and lower ITO layers. The design can guarantee the continuity of the upper and lower plates and does not affect the electric and magnetic fields generated by spiral microcoils, which are utilized to drive LC film to present needed functions of further controlling and adjusting incident microbeam distribution, which is preprocessed by main objective lens system. After an AC voltage signal is applied across the microcoil, an effective electromagnetic field can be formed in LC cell so as to drive LC molecules to rotate and thus demonstrates an electrically tuning focus. The simulations show that the design of patterned PNSMs can be effectively used to form a sufficient electric and magnetic fields that are directly used to rotate LC molecules and thus form a gradient refractive index distribution for converging incident microbeams so as to show a higher controlling-light efficiency than that of traditional patterned microelectrodes. The proposed method laid a solid foundation for future smart ECLCMAs.
Electronically controlled liquid-crystal microlens array with plane swing focus and tunable focal length
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In this study, a kind of electronically controlled liquid-crystal microlens array (LCMLA) with plane swing focus and tunable focal length instead of a commonly microlens array with a fixed focal length and then focus distribution for highresolution image acquisition, wavefront measurement, and distortion wavefront correction, is proposed. The LCMLA mainly consists of two glass substrates coated with a film of indium-tin-oxide (ITO) transparent material on one side. Each sub-unit top layer is composed of four sub-square electrodes, and the bottom layer is a circular electrode. The key technological steps in electrode fabrication contain an ultraviolet lithography, a dry etching (ICP etching), and final electron beam evaporation and overlay. The current LCMLA can be realized in three operating modes under external driving circuitry, including intensity image acquiring, wavefront measurement and distortion wavefront correction. The LCMLA is only in the image acquisition mode under the condition of no driving electrical signal. As the same driving electrical signals are applied onto the top four sub-electrodes of each sub-unit, the LCMLA is in the wavefront measurement mode. The LCMLA is in the key wavefront correction mode when different driving electrical signals are simultaneously applied onto the top four sub-electrodes of each sub-unit. Experiments show that the focal point of the LCMLA can be moved along the optical axis and over the focal plane by applying appropriate driving voltage signals.
Matrix distributed liquid-crystal microlens arrays driven by electrically scanning voltage signals
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Liquid-crystal material demonstrates a special property of optical anisotropy. So far, it is widely used in many fields including flat panel displaying and other various optoelectronic devices. Electrically controlled liquid-crystal microlenses have presented some unique capabilities such as swinging focus over the focal plane and tuning focal length only by electrical signals applied over them. According to the typical electro-optical characteristics of nematic liquid-crystal materials, a liquid-crystal microlens array (LCMLA) with a featured zoned quasi-single-microhole electrode with more controlling area than the past microelectrode structure developed by us, which is applied by a multiplexed controlling signals according to an electrically scanning fashion, is proposed for realizing a new type of dual-mode imaging including one addressable wavefront measurement and correction through sensor array zoned by LCMLA, and another intensity image. Each sub-electrode in a quasi-single-microhole electrode can be individually driving and adjusting. So, two operations of adjusting focus and swinging focus can be achieved only by applying suitable voltage signals over each subelectrode. However, to successfully achieve a dynamic compensation of the aberrated wavefront measured so as to minimize target image distortion, hundreds of LC microlenses are needed for measuring and reconstructing wavefront corresponding to realtime image acquired. This will lead to a problem: a large number of conductive wires cannot be effectively arranged and connected to the LC microlens. In this paper, a LCMLA based on an electrically scanning approach is proposed. An "active matrix" for applying voltage signal over different structural unit is used so as to realize a active control of wavefront measurement and correction corresponding to a target image.
Reflectance controlling based on surface plasmon polaritons stimulated over the surface of metallic nanostructures
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The surface plasmon polaritons (SPPs) is an electromagnetic wave that can be stimulated and then propagates over the surface of the preshaped metallic nanostructures or the interface between the surface of the metallic nanostructures and the substrate media due to a strong coupling of incident light and the surface free-electrons moving on the metallic nanostructure surface with a featured micrometer scale. As shown, through SPPs, incident light energy can be localized effectively in a sub-wavelength region or space, and thus so-called light diffraction limit can be break through easily. Therefore, it has demonstrated a good prospects for developing advanced functioned materials or devices such as light absorbing materials, optical antennas, and optical information storage modules. In this paper, we propose a special metallic nanostructures, which can be used to absorb a certain band of incident light by converting them into a kind of local freeelectron oscillation, which means that SPPs can be generated and processed efficiently. As shown, the metallic nanostructures will present a lower reflectivity in the wavelength range, and through adjusting several key parameters such as the period of the metallic nanostructures, we can achieve an effective control of reflectivity because a valley of the reflectivity curve can be formed, which means a low reflectance at a specific wavelength band has been obtained.
Study on cascaded stepwise singular value decomposition and its application in laser absorption spectroscopy
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During the detection process of atmospheric laser absorption spectroscopy in open space, the useful signal may be submerged in the noise due to the inherent noise of the instrument and external environmental noise. In order to effectively improve the signal-to-noise ratio, a new method of cascaded stepwise singular value decomposition has been proposed. By constructing different matrices, the low-frequency noise and high-frequency noise are removed in stages. A laser absorption spectroscopy atmospheric detection system in open space has been established to experimentally verify. The results show that, compared with the traditional method, the signal-to-noise ratio of the spectral signal processed by the method of cascaded stepwise singular value decomposition is increased from 0.211 to 1.029, the standard deviation is also reduced by 1.927 times. It is proved that the proposed method can effectively remove noise and obtain high-quality laser absorption spectrum signal to improve gas detection accuracy, which has practical value.
Steady object tracking based on online sample mining
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Tracking methods based on Correlation Filter have been constantly improved in tracking accuracy and robustness. However, it still challenged in background clutter, rotation changes and occlusion, the drift of the model was one of the main reasons. In this paper, we propose an online sample training method based on Gaussian Mixture Model. The maximum response value, obtained from the convolution of samples and filters, is used to judge the availability of the online samples, which is able to reduce the interference of wrong online samples. Then, through Gaussian Mixture Model, samples are classified to strengthen the diversity of the sample set, which can avoid model drift effectively. Besides, we also propose a model update criterion to enhance the stability of the tracker, and heighten the efficiency of calculation. This criterion is determined by changes of target in scale and displacement. We perform comprehensive experiments on three benchmarks: OTB100, VOT2016 and VOT-TIR2016. Comparing with other trackers, our tracker has better robustness in the condition of background clutter, rotation change and occlusion. Moreover, its speed also maintains real-time performance.
Corneal astigmatism axis standard based on toroidal surface design
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Cornea is an important part of human eye refractive system. Corneal astigmatism axis, as a key parameter to evaluate the corneal topography, is directly related to visual diagnosis and treatment. In 1997, International Organization for Standardization published the first ISO standard for requirements of corneal parameter measurement. However, due to the limitation of processing and testing technology at that time, the standard of corneal astigmatism axis has been an unsolved technical problem. Research work on corneal astigmatism axis standard was carried out early in 2007 by China National Institute of Metrology. In this paper, first, measurement principle of corneal parameter is described. Then, corneal astigmatism axis standard based on toroidal surface is designed and manufactured, which consists of axial model eye, axial sleeve and measurement support. Axial model eye is a square cylinder whose front surface is toroidal and back surface is scrub plane, which is located in the square through hole of axial sleeve, and axial sleeve is located on the trapezoid groove of measurement support. Next, by accurate measurement and metrological calibration, four axes of 0°, 45°, 90° and 135° are achieved and axis uncertainty U=0.3° (k=2). Finally, measurement results show that the newly developed astigmatism axis standard can realize the evaluation of corneal parameter testing instruments well. Besides, design structure specified in ISO standard is found to be hard for accurately location and infeasible in practice. A proposal for revision of this international standard will be drafted and discussed on ISO meeting of 2019 held in America.
Effect of the ratio of oxidizing agent to reducing agent on the performance of Mg/PTFE/ Pb3O4 pyrotechnics
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In order to study the effect of the ratio of oxidizing agent to reducing agent on the performance of the trilead tetraoxide/ Teflon/magnesium (Pb3O4/PTFE/Mg) powder decoy compounding agent, 5 different pharmaceutical formulations are designed by maintaining constant oxidant formula and changing the ratio of oxidant agent and reducing agent. Then the mixed powder is pressed into a powder by a table press. The combustion process of the drug column was measured with an 8-14 micron infrared thermal imager, and the burning time, mass burning rate, radiation area, radiance, and radiation intensity of each sample were calculated. The results show that with the increase of the proportion of reducing agent, the burninging time of the sample becomes shorter and the mass burninging rate becomes larger. The maximum temperature of the flame increased with the proportion of reducing agent first and then decreased. When the ratio of oxidant agent to reducing agent is 1.5:1, the maximum temperature of sample combustion reaches a maximum of 1503°C. The radiance increases first and then decreases with increasing proportion of reducing agent, and When the ratio of oxidant agent to reducing agent is 1:1.5, the infrared radiance is the maximum, which is 2510 W·m-2·Sr-1.Radiation intensity increases as the proportion of reducing agent increases. It can be seen that in the 8-14 micron band, when the ratio of oxidant agent to reducing agent is 1:1.5, the radiation characteristics of the sample is best and the sample is the best one as infrared decoy.
Research on cascaded Turbo-STBC coding based on GFDM-ROF system
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ROF is the technology that integrates optical communication and wireless communication. It not only possesses the characteristics of high speed and long distance in optical communication, but also has the characteristics of flexible in wireless communication. GFDM is one of 5G's alternative technologies for high-frequency millimeter waves. This paper proposes and verifies that in the GFDM-ROF system with MIMO, cascaded Turbo-STBC coding can improve the reliability of the entire system. We use Turbo code as the out-of-channel code, and STBC code as the intra-channel code. When using two transmitting antennas and four receiving antennas and the SNR is higher than 5 dB, the BER is below 10-6. Furthermore, based on this system, under high load communication conditions, we proposed an adaptive coding technology with excellent performance and it can reduce system load rapidly.
IR reflective characteristics of a periodic nano-pattern array shaped in a metallic film
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When a beam of TM electromagnetic wave with a matched frequency to a periodic nano-pattern array shaped in a metallic film is incident upon the metal interface, the surface free-electrons of the metal film will be stimulated and thus oscillate collectively. The phenomenon above means that the incident electromagnetic waves and surface free-electrons are coupled effectively and then a mixed excitation mode of surface plasmon polaritons (SPPs) are generated and also spreaded over the metal-dielectric or metal-air interface. According to current researches, the surface waves originated from a strong surface free-electron oscillation can propagate along a interface only being a micrometer scaled distance. When the energy and momentum of incident electromagnetic wave are suitable, a SPPs can be guided and thus a part of electromagnetic energy can be converged onto the metal tip, thereby reducing the surface reflectivity of the electromagnetic waves because they are already concentrated or storaged into the periodic nano-pattern array shaped. In order to study the influence based on several factors including metal surface structures, nano-pattern array period, and electromagnetic wave incident angle, an optical frequency SPP device is designed. The device with a gold plating film is fabricated over a silicon substrate, and then the substrate is etched so as to shape a metal nano-pattern array. The structure is called a sub-wavelength gold structure (SWGS). A virtual model is established according to CST microwave studio. The finite element method is also used to simulate the electromagnetic characteristics of the SPPs. Simulations are carried out to obtain reflectance waveforms so as to explore the reflectivity changes of SWGS irradiated by nearinfrared waves under different conditions including metal surface structural characters, nano-pattern array period, and electromagnetic wave incidence angles.
Blind phase noise compensation based on circular quadrature amplitude modulation
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A two-stage phase noise compensation (PNC) algorithm is proposed based on the circular multilevel quadrature amplitude modulation (C-mQAM). In the first stage, a cost function to estimate the phase noise roughly is constructed, before which the received symbols are classified by their amplitudes and rotated. It can be approximated to a cosine function, and three test phases are required for the calculation of its parameters. Kalman filter (KF), utilized in the second stage, provides the final estimation of phase noise. The performance of the proposed algorithm is evaluated with two aspects of computational complexity and the combined linewidth symbol duration product (△v·Ts) tolerance. The results show that the proposed algorithm offers a low computational complexity and high △v·Ts tolerance compared to the blind phase search (BPS) algorithm and extemded Kalman filter (EKF) algorithm.
Non-perturbation calculation for the dynamic problem of quantum many-body systems
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We propose a new method to discuss the evolution of physical systems, which has an analytic form. And we systematically introduce this new method by the example of Jaynes-Cummings model without rotation wave approximation. Simultaneously, while we repeat previous work by our method, we also calculate it by adding the time growth factor to the initial state unfolded in the steady state which is based on Fock state and is obtained by solving the time-independent Schrodinger equation (in this article, the traditional method refers to this method). By comparing these two results, we find the drawback of our method and improve it. Finally, we show that our improved method need the smaller Fock space than the traditional method for physical systems with two-mode cavity field and put forward expectations for the follow-up study.
Electro-optic mode deflection based on a lithium niobate waveguide with microstructured electrodes
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We propose the electro-optic mode deflection devices based on annealed proton exchange (APE) waveguides in lithium niobate with microstructured electrodes. Two mode deflection devices with right-triangle-shaped electrodes (Device A) and isosceles-triangle-shaped electrodes (Device B) are investigated. Taking advantage of the refractive index prism array formed when applying an external voltage to the electrodes, the mode can be deflected. Beam smoothing can be achieved by applying alternating voltages. A∼1.28 μm beam deflection is obtained by applying a voltage (20 V) for Device A. For Device B, a 3.52 μm beam deflection is obtained by applying a -15 V voltage to the electrodes. Device B has a horn-shaped input waveguide which ensures that the output is a quasi-single mode. The mode quality of the deflection beam is also quantified by the CMOS camera. Smoothing the non-uniform density distribution of light beam is confirmed by averaging over 69 images taken by the CMOS camera with alternating voltage. These electro-optic mode deflection devices have potential applications in electro-optic sampling, high-speed optical switch, and beam smoothing of a high-power laser.
Low cost and non-hermetic 100-Gb/s CWDM4 TOSA with silica-PLC AWG multiplexer
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We present a compact hybrid-integrated 4 × 25.78 Gb/s TOSA based on butt coupling between DFB-LDs and silica-PLC AWG multiplexer. To obtain a low cost TOSA, high-cost conventional hermetic ceramic metal box is replaced with nonhermetic metal box. Experimentally, we demonstrate that the TOSA could achieve error-free operation for a 10 km transmission at 25°C. The packaged CWDM TOSA, which is 15.8 mm × 7.0 mm × 6.0 mm in size, shows a side-mode suppression ratio of >40 dB, a 3-dB bandwidth of >18 GHz, and error-free transmission with an average optical output power of >0 dBm and dynamic extinction ratio of >4.0 dB at 25.78125 Gb/s over a 10-km single-mode fiber for all four lanes.
A dynamic bandwidth allocation algorithm based on neural network prediction-correction model and software defined TDM-PON
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In the future, with multiple services and large-capacity access network scenarios, the network load is often high but the bandwidth is limited. On the situation, based on the software-defined TDM-PON access network architecture and network traffic prediction-correction model, a dynamic bandwidth allocation algorithm is proposed. In the algorithm, a prediction model is used to predict traffic information and a correction mechanism is used to correct the prediction model. After analyzing the global information of the network, the algorithm provide corresponding bandwidth management policies based on business priorities according to different network load conditions. We compare this algorithm with IPACT algorithm, unused prediction algorithm and neural network prediction without correction. It proves that the algorithm guarantees the service quality requirements of different priority services when the bandwidth is limited and the network load is high, and it performs better in terms of average packet delay, bandwidth utilization, etc. Simulation shows, compared with the traditional strategy, the average packet delay is reduced by 70%, and the bandwidth utilization is increased by 19%.
Research on temperature sensor of double-cone-section cascading interferometer
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This type of sensor is manufactured by using the KF-FBT type fusion taper machine to uniformly pull the same single mode optical fiber. Double tapered section cascade type singles mode fiber. When the signal light passes through the concatenation fiber cone, the cladding mode is excited after passing through the first stage cone region. After a certain distance transmission, the second stage cone region interferes with the core mode. The change of the waveform is seen from the spectrometer. When the two cones are bent by 90, the article explores a double-cone-section cascading sensor that is easy to operate and easy to perform multi-point measurements from both theory and experiment. The spectral peak-to-valley contrast of the interference fringe is more obvious, and it can serve as a sensor head to test the ambient temperature. The sensor has a temperature sensitivity of 60 pm/°C.
High-gain amplification of weak signal based on stimulated Brillouin scattering in optical fiber
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Lidar has been widely used in both military and civil applications. Its received optical signal undergoes considerable loss and disturbance from background noise, which limits its performance especially in bad weather or air conditions. A high-gain and frequency-selective amplifier for weak optical signal based on stimulated Brillouin scattering in single mode fiber is proposed, which is an excellent candidate for the signal enhancement in lidar system. The characteristics of the amplifier were studied numerically and experimentally. In experiment, a 430-nW (peak power) pulsed signal was amplified by 70 dB with a signal-noise ratio of 14 dB, which was in good agreement with theoretical result.
Ultra-long focusing of microsphere lens via wavefront reconstruction in microsphere
Jinzhong Ling,
Dancui Li,
Xin Liu,
et al.
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Due to the properties of super-narrow focusing and super-resolution imaging, microsphere lens has attracted many attentions. In order to operate the microsphere lens freely, a microsphere holder is necessary to control its 3-D motions accurately. In this paper, a stable and practical microsphere holder is designed for microsphere lens scanning imaging. Furthermore, we numerically analyzed the influence of microsphere holder on the focusing properties of microsphere lens. With the reflections from the surface of microsphere holder, the wavefront in microsphere could be reconstructed through the interference between the incident light and reflection beams. At proper conditions, the curvature radius of incident wavefront in microsphere could be enlarged by the reflections beams, which could generate longer focal length of microsphere lens. Meanwhile, the width of focal spot is almost constant, which is as narrow as the one without microsphere holder. Therefore, the microsphere holder will almost not reduce the imaging resolution of microsphere lens, but enlarge its working distance obviously, which is significant for microsphere assisted far-field super-resolution imaging. Through the optimization of the opening angle and the material of microsphere holder, an ultra-long working distance of 6.5λ has been achieved by microsphere lens with a proper microsphere holder. This holder could be applied for microsphere assisted far-field super-resolution imaging due to its contribution on microsphere lens control and focal length increase from near-field to far-field, and extend the applications of microsphere assisted nano-imaging into more fields and more samples.
Dual-wavelength Tm, Ho:LLF laser operating at 1895 and 1950 nm
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We demonstrated a dual-wavelength Tm,Ho:LuLiF4 laser operating at 1895nm and 1950nm by adjusting the pitch angle of the output coupling mirror. With a X-type four-mirror cavity, a total output power of 575 mW is achieved at an incident pump power of 2.1 W, which corresponding slope efficiency is 27.95% and the threshold power is low to 110 mW. The dual-wavelength laser is very useful for the generation of coherent light source in terahertz band.
Imaging through highly scattering media based on optical transmission matrix
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The inhomogeneity of scattering media will distort the propagation of the waves, which is detrimental to the performance of optical imaging. Although various approaches have been proposed recently to overcome this problem, they are not suitable to image the rapid-movement objects as a long sequence of measurement steps are required. In this paper, based on the optical transmission matrix of the scattering medium, we show that the information of the object can be recovered directly from the distorted output optical field. Especially, our method is effective to the thick scattering medium. We predict it might have the potential application for real-time imaging.
Large scale and high resolution color fresnel holographic 3D display using RGB LED illumination
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In this research, a color grating projection system is designed to effectively and flexibly display spatially sampled large size and high resolution color Fresnel hologram. The sampled color Fresnel hologram is placed in the image plane of projection system. The parameters of color grating are adjusted for 3D color display. Specifically, one effective scheme of spatially sampled color Fresnel hologram is used for reducing the data redundancy of computer generated Fresnel hologram while keeping a high resolution of reconstructed 3D image. A hologram with the size of 30mm×30mm at the resolution of 94208×94208 is calculated and optically reconstructed to verify the proposed display system.
A polarization insensitive infrared filter based on a liquid-crystal Fabry-Perot for electrically tunable spectral imaging
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This paper presents a polarization insensitive infrared filter based on a liquid-crystal Fabry-Perot (LC-FP) developed for electrically tunable spectrum and performing high efficient imaging detection. Generally, the LC-FP filters are polarization sensitive optical devices, which means that filtering effect will be enormously influenced by ray polarization so as to lead to a low utilizing efficiency of incident energy. Therefore, it is of great significance to find an approach to improve or even solve the problem. The new type of infrared filter designed by us is mainly consists of a FP resonant cavity with a layer of zinc selenide (ZnSe) material as its substrate and a thin film of nano-aluminum (Al) material acting as its electrode and high-reflection mirror. Particularly, compared to the common filters, it has a multi-directional layer of ployimide (PI) film which can make the LC distributed along two mutually perpendicular directions so that the incident infrared light in different polarization orientations are able to be modulated. The experiment results indicate that the filter’s polarization insensitivity is substantially improved, thus it can work well in various polarized infrared radiations, and obviously will have a broader prospect of application.
Fast hologram calculation using wavelet transform
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To further accelerate the calculations associated with point-cloud-based holograms, wavelet shrinkage-based superpositIon (WASABI) has been proposed. Wavelet shrinkage eliminates the small wavelet coefficient values of the light distribution emitted from a point cloud, resulting in an approximated light distribution calculated from a few representative wavelet coefficients. Although WASABI can accelerate the hologram calculations, the approximated light distribution tends to lose the high-frequency components. To address this issue, random sampling was applied to the light distribution.
Light intensification by ceria on the surface of fused silica
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The intensity distribution of an initially plane wave incident on ceria in subsurface layer is calculated numerically with Finite-different time-domain (FDTD) solutions.The results show that the light intensity enhancement is caused by lens effect due to the high refractive index of ceria, and the surface damage characteristics of fused silica is very sensitive to location of ceria, ceria size and incident wavelength. The ceria located on the exit surface of fused silica generates electric field enhancements that are stronger than those on the entrance surface. The increasing of ceria size can lead to higher light intensity enhancement factor (LIEF) and the LIEFs can reach two orders of magnitude when the diameter of ceria is three times that of the incident wavelength. The light intensity enhancement caused by ceria with the same location and diameter decreases with the increasing of wavelength. As ceria on polished surfaces is randomly oriented, the probaility for large intensity enhancements to occur is high. The model may provide effective support for research on laser-induced damage and improvement of processing technology for fused silica.
The design of two-lens slit spatial filter for high power laser system
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The slit spatial filter can be used in high-power laser system. The performance of two-lens slit spatial filter is described and discussed. The laser intensity at the slit edge and the peak intensity of the focal line with different F-numbers and the cut-off frequencies are compared with that of the traditional spatial filter. Simulation results show that the laser intensity at the slit edge and the peak intensity of the focal line are less two orders of magnitude than that of the traditional spatial filter. Besides, the vacuum degree required in the slit spatial filters is about 10-1 Torr, which is less two orders of magnitude than that of the traditional spatial filter.
Paint removal based thermal stress with a high repetition pulse fiber laser
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Paint removal based thermal stress with high repetition pulse is considered in this paper. The temperature distribution of aluminum substrate and paint under laser irradiation is simulated and the thermal stress generated by thermal expansion is calculated. The adhesion force between the paint and the substrate was calculated according to adhesion formula. The conditions for the paint removal can be obtained by comparing the force of thermal stress and adhesion. At the scan speed of 5000 mm/s, the fiber laser with wavelength of 1064 nm, pulse width of 240 ns and frequency of 100 kHz is used to strip red paint from aluminum without any damage. And the stripping effect at the different output power is also taken into account.
Analysis of laser-induced damage in optical thin film based on ANSYS
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The electric and thermal effects of optical thin film irradiated by Gaussian-pulsed laser are simulated with finite element method (FEM) based on the software ANSYS. The electric field intensity distribution of HfO2/SiO2 high reflective (HR) film is investigated. The transient heat-conduction model of the film is established for the calculation of temperature field of optical thin film coating. Simulation results show that, multilayer films are more prone to damage than single film, and the upper layer of HfO2 layer in the spot center may easily be damaged.
Infrared small target detection using phase spectrum of quaternion fourier transform
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Infrared small target detection is one of the key techniques in infrared search and track system, and the essence of infrared small detection is background suppression and target enhancement. Inspired by that fact that phase spectrum is proved to be more effective to extract the salient areas than the amplitude spectrum of Fourier transform, a new infrared small target detection method based on phase spectrum of quaternion Fourier transform (PQFT) is proposed in this paper. First of all, four features including intensity, motion, gradients of horizontal and vertical directions are used to construct a quaternion of PQFT. Then, the target enhancement map that highlights the salient regions in the time domain is computed using the inverse PQFT. At last, the real target is directly segmented by an adaptive threshold. Both qualitative and quantitative experiments implemented on real infrared sequences evaluate the proposed method, and the results demonstrate that our method possesses more robustness and effectiveness in terms of background suppression and target enhancement when compared with other conventional methods.
Laser cleaning soil rust layer on the surface of ceramic artifacts
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In this paper, the laser cleaning soil rust layer on the surface of ceramic artifacts by the way of ablation and thermal stress with infrared high-repetition pulse laser is carried out. A cleaning effect can be achieved with laser scanning 10 times at the speed of 480 mm/s and fluence of 795.7747 J/m2 near the ablation threshold. However, the external force is required to make the soil rust layer fallen off. In contrast, a better cleaning effect that the soil rust layer is directly peeled off under the effect of thermal stress without ablation at the contact surface and external force can be observed with the fluence of 1591.5494 J/m2 and laser scanning at 1 time. Furthermore, a two-layer structure model is built to analyze the mechanism of cleaning by thermal stress based on the heat conduction and thermal stress equation. The maximum peeling thermal stress at the contact surface is 2.854×107 N/m2, which is greater than the adhesion stress of 2.050×107 N/m2. This is in agreement with experiments.
Two-step phase retrieval algorithm from single-exposure measurement
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Reconstruction of the lost phase information in the complex optical field from a single-intensity measurement in the Fourier domain is often termed as phase retrieval. This method can be used in many fields, such as electron microscopy, wavefront sensing, astronomy and crystallography and so on. The classical phase retrieval methods use the two-intensity measurements recorded or single-intensity measurement recorded with some prior knowledge, which utilizes the Gerchberg-Saxton(GS)-like algorithm to iteratively recover the phase of the complex optical field. Aiming at the problem that the single-intensity phase retrieval method has poor reconstruction quality and low probability of successful recovery in practical application, an improved method is proposed in this paper—two-step phase retrieval algorithm from single-exposure measurement. Our proposed method divides the phase retrieval into two steps: first, the GS algorithm combined with prior knowledge is used to recover the amplitude information in the spatial domain from the single-spread Fourier spectrum, and then the classical GS algorithm using two-intensity measurements (one is recorded and the other is estimated from the first step) is used to recover the phase information of the complex optical field behind the coded aperture. Finally, the effectiveness of the proposed method is verified by numerical experiments. Compared with the single-intensity phase retrieval method, our proposed method can significantly improve the reconstruction quality and probability of successful recovery.
Simulation of different samples size on 2.52THz compressive holographic tomography
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Terahertz compressive holographic tomography has been one of the most investigated research topics ever since the generation of terahertz signals. The accuracy of the 3D reconstruction results are influenced by samples size directly. This paper mainly studies that different samples size influence the compressive sensing algorithm iteration number and sparse restriction parameters on the 2.52THz reconstruction results under Gaussian noise conditions. The best reconstruction parameters are given and compared with condition of no noise. This simulation study is possible benefit to the practical application.
Compact waveguide (de)multiplexer based on asymmetric Y-junctions
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A four-order asymmetric Y-junctions mode (de)multiplexer ((de)MUX) was theoretically proposed for highly integrated on-chip mode-division systems. The high-order mode in the stem waveguide of asymmetric Y-junctions is designed to be separated from the lower-order mode and evolve into the fundamental mode in the narrow arm. Through the widths optimization of branch arms by effective index matching and beam propagation method, the footprint of four-order mode (de)MUX was controlled to be 140×7.1μm2. The calculated excess loss and crosstalk were less than 0.3 dB and -18 dB within the operation wavelength range from 1460 to 1660 nm, respectively. This scheme may be expanded to higherorder modes (de)MUX design.
Broadband light-control-light characteristics of WS2 on microfiber
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Light control-light characteristics of a micro fiber (MF) coated with tungsten disulfide (WS2) nanosheets is demonstrated in this paper. A device with WS2-coated MF has been fabricated, and the transmitted optical powers of the device are measured with 405 and 660 nm pump lasers. By tuning the pump lasers, we achieve the all light controllable sensing of WS2-coated MF over a broadband wavelength range from 1520 to 1620 nm, offering competitive sensities of 0.238 and 0.136 dB/mW for 405 and 660 nm pump lasers, respectively. In addition, The rise and fall times of the transient response to pump lasers are also measured. For the 405 nm laser, the rise and fall times of the transient response are 0.32s and 0.42s, respectively. For 660 nm laser, the response times toward the presence (removal) of the pump light transient response are 0.28s and 0.37s, respectively. Experimental results indicate that the device integrated with WS2 could hold promising potentials in photoelectric and photonic applications.
A large relative aperture and wide-spectrum star sensor optical lens design
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Star sensor is a high accuracy sensitive instrument for attitude determination, and the optical system is an essential part of the star sensor. According to the user requirements and CODE V patent library, the optical lens of a star sensor with large relative aperture and wide-spectrum range is optimized. The final design consists of 8 spherical lenses. The focal length is 50mm, the relative aperture is 1/1.35, the field of view is 7° × 7° (the diagonal field is 9.9°), and the spectral range is 500nm to 800nm. The design results show the optical lens has good performance. The distortion is less than 1%, the energy concentration is more than 80%, and the MTF of all fields of view is close to each other. The energy concentration of the spot diagram on the off-axis field of view and the on-axis field of view remains basically the same. The optical system meets modern design requirements for the star sensors.
Diagnosis of lichen sclerosus based on multiphoton microscopy
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Lichen sclerosus (LS) is a chronic inflammatory dermatosis that caused substarntial discomfort and morbidity. Early diagnosis and treatment can prevent the occurrence of squamous cell carcinoma (SCC). Multiphoton microscopy (MPM) has the potential as an effective, noninvasive diagnostic tool for tissues imaging at a molecular level. The technique has several advantages including deeper penetration depth and minimal photo-toxicity and photo-bleaching compared with other microscopy techniques. In this work, MPM was expand to histological investigations, differentiating LS lesion from normal skin by imaging unstained histological sections without hematoxylin and eosin (H and E) staining. Our results present that MPM has the ability to identify the characteristics of LS including the changes of hyperkeratotic epidermis, homogenized collagen, and inflammatory cell infiltration. These tissue architecture details are in perfect agreement with the corresponding H and E-stained images. In addition, the results of collagen content show significant difference in normal skin and LS. The studies indicate that the MPM technique not only has the ability comparable to the H and E-stained images to distinguish between normal tissue and LS, but also can provides more comprehensive diagnostic information for the pathologist. With the advent of the clinical portability of MPM, this technique has the potential to be a powerful tool for diagnosing LS and monitoring the treatment response in vivo.
Manipulating electromagnetic wave propagation with negative-zero-positive index magnetic metamaterials
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Based on the multiple scattering theory and effective medium theory, we demonstrate that flexibly molding the propagation of electromagnetic waves can be realized by designing magnetic metamaterials (MMs) with an array of ferrite rods. By calculating photonic band diagrams and effective constitutive parameters, it is shown that MMs can be used to achieve effective zero index with both the effective permittivity and permeability close to zero, a matched zeroindex material (MZIM). The transmitted Gaussian beam exhibit zero phase delay when it pass through the MZIM slabs with different thicknesses so that the spatial phase change of electromagnetic waves can be regulated, thereby realizing a diversity of electromagnetic wave-front modulation. In particular, the effective index of MMs can be tuned from negative to zero and to positive by controlling bias magnetic field (BMF), resulting in the switching of beam reflection and refraction. The working frequency of MZIM can also be tuned by controlling BMF, adding additional degree of freedom. Moreover, the gradient index MM can be realized by applying a gradient BMF, which can provide an additional parallel wave vector so that the direction of transmitted beam can be controlled more flexibly by controlling the gradient of BMF, which is more convenient for the designing electromagnetic devices.
Improving accuracy of high precision displacement measurement system with optical pickup head by using differential astigmatism focus error detection
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Measurement of the surface profiles of machined workpieces is becoming increasingly important to the progress of ultra-precision engineering. Optical non-contact probe is fit for measuring small, thin, soft parts, and it will not cause abrasion damage for the fragile surface of the workpiece. Astigmatic detection systems (ADS) based on the commercial digital versatile disk (DVD) optical pickup heads (OPH) are in widespread use for this purpose due to its well-established standards, high detection bandwidth, compact size, low cost and ease of use. Unfortunately, it has some serious drawbacks relating to issues concerning about dynamic characteristic, low stability and accuracy. In this paper, a high precision displacement measurement system was constructed with a modified DVD optical head by using differential astigmatism focus error detection. The proposed system is cost-effective to quickly accurately estimate and correct systematic errors of four quadrant detector (4QD). Moreover, based on replaceable micoscope objective and automatism testing system of 4QD, it can also detect the two-dimensional angular tilt of the object surface. Our experimental results demonstrated that the OPH showed about 8um measuring range and 20nm resolution.
The ultra-stable microwave based on ultra-stable laser
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An ultra-stable microwave (USM) based on an ultra-stable laser (USL) and fiber optical frequency comb (OFC) is built at the National Institute of Metrology (NIM), China. The sum frequency of the carrier envelope offset frequency of FOFC and the beating frequency between the USL and FOFC is stabilized with an 100MHz microwave signal which is controlled by the H master. The error signal controls the pumping laser power through the pumping current and the cavity length by the piezoelectric transducer (PZT). Meanwhile, the error signal is send to the temperature control part of the optical resonant cavity for the long term stability. The stability of the USM is 1.33E-14 at 1s. The whole USM system is much robust, and can continuously running more than 30 days. This USM will be applied as the local oscillator for NIM5 Cs fountain to improve its short term stability.
Anisoplanatic imaging of space target based on multilayer phase screens
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Atmospheric anisoplanatic effect is an important problem to be solved in telescope observation of space target imaging. Numerical simulation of atmospheric anisoplanatic imaging is the basis for studying the restoration of anisoplanatic images. Based on the propagation theory of light waves on the inhomogeneous turbulent path and multilayer phase screens distribution model, this paper establishes a theoretical model of atmospheric imaging for space targets under anisoplanatic conditions. The near-surface atmosphere can be divided into several stratifications of atmosphere at different altitudes. Find out the best phase screen distribution location for each atmospheric stratification, and use the multilayer phase screens at different altitudes to represent the atmospheric anisoplanatic effect. The phase change of the light wave emitted by each point on the space object through the atmosphere is represented by a phase screen, and the final phase size is the superposition of the phase of the light wave passing through the phase screens of each layer. A series of spatial target images are simulated by different layers of phase screens for anisoplanatic imaging, and combined with theoretical analysis to find the best phase screen position and the number of layers. The experimental results show that the three-layer phase screen can accurately simulate the atmospheric anisoplanatic imaging while maintaining the computational efficiency, and effectively reflect the changes of the point spread function (PSF) when the spatial position changes. The imaging results have no ringing and edge effects, and can accurately represent the influence of atmospheric anisoplanatic effect on atmospheric imaging.
Filtering and reduction for 3-dimensional surface modeling of laser line scanning point cloud
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With 3D laser scanning technology, it is possible to record clear and abundant surface information of the measuring object, but it also contains a large amount of redundant information. Because of the complexity of measurement environment, the 3D data obtained by camera contains a large amount of noise, which increases the difficulties of 3D visualization, feature extraction and recognition. In this paper, classical 2D filtering algorithm and 3D spatial clustering are combined for applying to 3D point cloud, which can preserve as much detail as possible on the surface of measured object. Then, Non-Uniform Rational B-Splines (NURBS) surfaces are used for reconstructing the surface of the object from filtered point cloud. In order to reduce the computing time in the reconstruction process while reduce the losses of surface information of the object, a simplification algorithm for point cloud that can preserve the geometric features of the object surface is proposed. The proposed algorithm has explicit significance in surface reconstruction of point cloud with noise, feature extraction and recognition in the future work.
Study of RGB-D point cloud registration method guided by color information
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The RGB-D camera can simultaneously acquire the color and depth information of the target surface, and has been widely used in 3D modeling, machine vision and other related fields. The traditional point cloud registration algorithm only considers the geometric information, it’s operating efficiency is low and the initial value requirement is high. This paper presents a new approach to align different frames point cloud obtained by RGB-D camera, which considers visual textures and geometric information simultaneously. Firstly, detect and match feature points on RGB images, and use RANSAC algorithm to eliminate the wrong matches. Then, convert the 2d matching pairs to 3d feature point cloud based on the depth camera model, and these point pairs without deep data are deleted. Finally, calculate the camera pose parameters by performing the iterative closest point(ICP) on feature point cloud, and apply the calculated pose parameters to the whole frame data. The experimental results show that, (1) In SIFT, SURF, and ORB feature point extraction operators, ORB has the best performance for point cloud registration. (2) The proposed algorithm has a high registration accuracy, the rotation and transform estimation error are less than 0.0097 and 4.2mm respectively. (3) The algorithm also significantly improves the convergence speed, only require 0.138 seconds, and it can meet the real-time processing requirements. (4) The algorithm is insensitive to the initial values and has strong robustness.
Image edge detection based on Sparse Autoencoder network
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Edge detection plays an important role in image pattern recognition. Because of the shortcomings of poor anti-noise and spurious edges by using traditional edge detection methods. A method of image edge detection based on Sparse Autoencoder neural work is proposed in this paper. This method uses Berkeley Segmentation data set to extract the highdimensional edge features of sample data by training the sparse autoencoder. Through the ZCA (Zero-phase Component Analysis) whitening treatment, the correlation between images is effectively reduced. The standard edge images are input into a Softmax classifier to train a classifier that can classify the edge features of each pixel. Last, the extracted features of each pixel sample are input into the trained Softmax classifier to classify the edge pixels to achieve edge detection. Experiments show that the algorithm has good noise immunity and certain application value.
Quantitative analysis of imaging quality of the segmented planar imaging detector
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The segmented planar imaging method is a new imaging concept based on Van Cittert-Zernike theory that offers significantly reduced size, weight, and power consumption compared to a traditional imaging system and aims to realize high resolution imaging. In this paper, the segmented planar imaging detector (SPID) imaging process has been accurately modeled and quantitatively analyzed to image quality enhancement. The influences of the longest interferometer baseline and the spectral channel number of array wave-guide grating(AWG) on the imaging quality of the SPID have been analyzed. It is verified that the cut off spatial frequency and the resolution of the SPID system is determined by the longest interferometer baseline Bmax. The imaging process of different Bmax have been numerical simulated to evaluate the impact of longest interferometer baseline on the SPID system, and the reconstruction image shows that the imaging quality can be improved by increasing the longest interferometer baseline. Also, the numerical simulations of different number of spectral channels of AWG have been operated, and the results showed that the visibility of interference fringes and spatial frequency coverage points are increased with the increasing number of spectral channels. Therefore, the imaging quality improved with the increasing number of spectral channel of AWG. In conclusions, the research results will provide theoretical and technical supports for segmented planar integral optical imaging system development.
Asymmetric electromagnetic wave propagation supported by magnetic metamaterials and graded photonic crystals
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Based on the multiple scattering theory and Mie theory, we have investigated two types of electromagnetic systems with broken symmetries, which are used to manipulate the propagation of electromagnetic waves. The former one is magnetic metamaterial made of an array of ferrite rods arranged either in periodic or non-periodic configurations, which bears the time-reversal-symmetry (TRS) breaking by applying a bias magnetic field. It can act as a perfect unidirectional absorber that can absorb the incident beam at a specified direction completely, while reflect nearly one half of the incident beam at the symmetrically opposite direction. The underlying physics lies in the excitation of magnetic surface plasmon that behaves differently for various incident directions. The phenomenon can also be understood by calculating the photonic band diagrams and effective constitutive parameters. The latter one is all-dielectric complex graded photonic crystal (GPC) consisting of dielectric rod dimers with a rotational gradient introduced layer by layer, which therefore breaks the spatial inversion symmetry of the system. The GPC is shown to split the incident beam into two separate ones, while for the light beam incident from opposite direction the focusing effect can be observed. The phenomenon can be interpreted by calculating the photonic band diagrams and iso-frequency curves. By tuning the gradient, the performance and the efficiency can be further controlled. The comparative study of configurations with two kinds of broken symmetries is significant for the understanding unidirectional wave propagation and the design of related electromagnetic devices.
Application of segmentation threshold method and wavelet threshold denoising based on EMD in Φ-OTDR system
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The sensing distance of the traditional phase-sensitive optical time domain reflectometry (Φ-OTDR) distributed optical fiber disturbance sensing system can only reach about 26 km. In order to increase the sensing distance without introducing the new technology and increasing the system cost, a method of processing the data by segmenting thresholds was proposed to increase the system sensing distance to 53.6 km. The locating accuracy is up to 20 m. Considering the impact of noise signal on the system's false alarm problem, a wavelet threshold denoising method based on empirical mode decomposition (EMD) is proposed. Experimental tests show that the method can significantly reduce the noise in the scattering signal and improve the alarm performance of the system.
Experimental investigation of laser shock peening on TC17 titanium alloy for thin-wall workpieces
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To study the performance and microstructure of TC17 thin-walled parts in shock wave and its reflection wave induced by laser, TC17 titanium alloy samples are processed using YAG laser with the wavelength of 1064 nm, pulse energy of 7J and pulse width of 15ns. Thus, its residual stress, microhardness and microstructure of overlapping shock with different thickness are obtained. The results show that with the thickness increasing, the front micro-hardness increases, and the reverse micro-hardness increases firstly and then decreases. The variation of residual stress with the thickness is consistent with the micro-hardness. The front residual stress maximum reaches -496.5MPa at the thickness of 5mm, and the reverse residual stress maximum reaches -171.1MPa at the thickness of 2mm. With the increase of thickness, the distribution of surface dislocations is more uniform, the grain refinement effect is more obvious, and the strengthening effect is the better. The causes of the variation of the double-sided residual stress field with the thickness are explained by theoretical analysis of the propagation and reflection of the shock wave in the material. The conclusions of this investigation have significance for the optimization of laser shock peening thin-wall workpieces.
One dimensional photonic crystal/metal structure hollow fiber refractive index sensor based on Tamm plasmon polariton
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A high performance hollow fiber (HF) refractive index (RI) sensor utilizing Tamm plasmon polariton is proposed. The structure of the sensor is a HF with the one dimensional photonic crystal (1DPC)/metal multi-films coated on the inner surface of supporting tube. Theoretical analysis based on a ray transmission model is carried out to evaluate the performance of the designed sensor. Because the lights transmitted in the HF have much larger incident angles than those in the prism based sensors, the center wavelength of the 1DPC should shift to longer wavelength. The origin of multiple resonance dips in the transmission spectrum is investigated by calculating the electric field distribution in the 1DPC/metal structure. The variation of the RI detection range of the sensor with different bilayer period is also analyzed. The optimal bilayer period of the sensor for achieving the highest figure of merit (FOM) at different sensed RI is obtained. Compared to the convention HF surface plasmon resonance sensors which can only detect sensed medium with RI higher than that of the supporting tube material, the RI detection range of the proposed sensor is largely extended to 1.33-1.60 while the FOM is enhanced several times.
Propagation properties of elliptically polarized light in one dimensional photonic crystal with a magneto-optical defect layer
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The propagation properties of elliptically polarized light in one dimensional photonic crystal with a magneto-optical defect layer is studied. The one-dimensional photonic crystal is composed of GaAs (H) and Ta2O5 (L), the defect layer material is magneto-optical material Ce:YIG (M), and the structure model of one-dimensional photonic crystal with a magneto-optical defect layer is designed as (L/H)N/M/ (H/L)N. The propagation properties of elliptically polarized light is calculated numerically by using the 4 × 4 transfer matrix method, and the possibility in the polarization controller is discussed. The results shows that the polarization state of the elliptically polarized light is changed with the increase of applied magnetic field, when the center wavelength is 1550 nm, N=8 and the phase difference (φX-φY) of the incident elliptically polarized light is π/6 the transmittance of elliptical polarized light is decreased from 1 to 0.6404, and the phase difference (φX-φY) is increased from π/6 to 0.3565π; then, when the center wavelength is 1550 nm, the applied magnetic field remains unchanged and the N is changed from 1 to 9, the transmittance of the elliptical polarized light is decreased from 1 to 0.2343, and the phase difference (φX-φY) is increased from π/6 to 0.7363π.
A fine-grained recognition model of air targets based on bilayer faster R-CNN with feedback
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The accuracy of air target identification is of great significance for air defense operations and civilian management. A fine-grained recognition model of aerial target based on bilayer faster regions with convolution neural network (Faster R-CNN) with feedback is proposed in the paper. Faster R-CNN model is a typical target detection model based on deep learning. However, its ability to distinguish categories with subtle differences is not enough. In the proposed model, Faster R-CNN model is used for the first training to get a classification model and the clustering analysis of the classification result is used to get confused categories. Then the first training model is fine-tuned to retrain the confusing categories. The model is tested in the FGVC-Aircraft-2013b data set, and the average training accuracy is raised from 88.7% to 89.3%, the accuracy of the classification is raised from 88.98% to 91.21%, which shows that this model is effective in improving the fine-grained identification of air targets.
High-sensitivity temperature optical sensor based on long-period fiber grating
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We propose a high-sensitivity temperature sensor with a long-period fiber grating (LPFG) using Mach-Zehnder and Sagnac interference of the optical path. The LPFG sensor achieved a good repeatability and stability of temperature response with a sensitivity of 0.083nm/°C in the range of 40°C-120°C. Comparing to the traditional fiber Bragg grating (FBG) sensor, the LPFG sensor shows 10 times higher temperature sensitivity than that of the FBG, so the problem of low sensitivity of FBG is solved. Otherwise, Mach-Zehnder and Sagnac interference of the optical path have the advantage of simple structure and good practicability which can replace the complex optical path in the special environment.
3-Dimensional surface inspection system for pantograph in railway nondestructive testing based on laser line-scanning
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In this paper, a detection system which combined with the line-structured light scanning technology that can visualize the pantograph surface and automatically locate and evaluate the wear condition of the pantograph is proposed. In this system, a three-dimensional camera and a line laser generator are used for acquiring surface data of pantograph. Then Laplacian filtering is used to smooth the data. Proceeded data and standard model are registered by using distance constrained ICP algorithm which combined with geometrical symmetry of pantograph. In this paper, a method to locate and quantify the wear area of the pantograph is proposed, which provides a feasible solution for inspection and visualization of pantograph wear.
Application of spectroscopy in prenatal testing
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In recent years, the incidence of congenital malformations was increasing obviously due to the significant increase in the number of women with advanced maternal age after the implementation of two children policy in China. Traditional prenatal testing methods faced the problems of the high risk of miscarriage, low sensitivity, and time-consuming. Development of a novel method with the features of noninvasive, rapid, cost-effective and high sensitivity will be of vital clinical value for prenatal testing. This review provided an overview of the common birth defects and compared the merits and drawbacks among current most-used prenatal detection methods. The characteristics of spectroscopic technologies, as well as their applications in prenatal testing were summarized. Spectral karyotyping, real-time fluorescence quantitative PCR, SNP allele site analysis, etc. using fluorescence spectrum analysis method and Raman spectroscopy have been reported in the application of prenatal testing. Finally, a new idea by taking the advantages of SERS for Down syndrome detection in pregnant woman blood was proposed, which may be providing a promising approach for realizing rapid, sensitive and noninvasive prenatal testing.
A blurry low-light image enhancement and deblurring fusion algorithm
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Due to the vagueness of mobile video shooting at night, the blurry low-light images obtained from it hindered humans from acquiring visual information and computer vision algorithms. In this paper, to lower color and lightness distortion when increasing visibility, a novel brightness mapping function based on the camera mapping model was proposed by using the chi-squared distribution. Then, the well-exposed images were obtained by using the brightness evaluation technique and the brightness mapping function. Finally, an existing image deblurring algorithm based on convolution and dark channel was employed to help deblur well-exposed images. Experiments showed that our method could achieve accurate contrast and lightness enhancement than several state-of-the-art methods and obtain decent sharp well-exposed images.
Growth, structure and optical properties of ZnSe:Co thin films
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ZnSe:Co thin films were grown on quartz substrates at various ambient pressure by pulsed laser deposition. The propagation of plasma plume, the structure and optical propert ies of films at pressure of 1Pa to 10Pa had been investigated. With the ambient pressure increased, the angle of divergence and propagation distance of plasma plume changed, the crystal structure of films investigated by XRD showed that the crystal quality of films was promoted. The optical band gap and refractive index were analyzed by the transmission spectra. The optical band gap first decrease then increase with increasing deposition pressure, which may be associated with the quantum confinement effect. The refract ive index increased with increasing deposition pressure, which may be due to the promotion of the film density. The dispersion parameters, E0, Ed, the static refract ive index (n0) and static dielectric constant (ε0) were calculated according to the single oscillator model.
Identification of specific histological characteristics of glioblastoma based on multiphoton microscopy
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Glioblastoma (GBM) is a highly malignant and rapidly invasive astrocytoma, which has explosive biologic properties with rapid clinical progression leading to death and has a poor clinical outcome. The average survival time of most patients is only 12 to 15 months. GBM is distinguished pathologically from lower grade tumors by ‘pseudopalisading’ necrosis and microvascular hyperplasia. The most exaggerated form of microvascular hyperplasia is called glomeruloid body. MPM is a potential tool for imaging biological tissues at the molecular level. In this paper, MPM based on twophoton excited fluorescence (TPEF) and second harmonic generation (SHG) was applied for identifying the GBM without labeling or fluorescent markers. The results showed that MPM can display the specific histological characteristics of GBM including ‘pseudopalisading’ necrosis and glomeruloid vascular proliferation. The results obtained are consistent with the diagnosis of pathological findings. MPM will become a promising imaging tool for preoperative diagnosis of glioblastoma in the future.
Influence of the evanescent waves on the imaging characteristics of microspheres
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We add a 20-nm-thick SiO film between a fully immersed BaTiO3 glass (BTG) microsphere and a sample with subdiffraction features, and study its imaging properties. Compared with a fully immersed BTG microsphere without the SiO film, the magnification becomes larger, and the initial image position is farther away from the sample. The imaging rules no longer satisfy the imaging rules used in geometrical optics. We propose that the thin SiO film can enhance evanescent waves and the enhanced evanescent waves affect the magnification and the image position in BTG microsphere imaging. Our studies will help to understand the imaging rules of microspheres more comprehensively.
Analysis of fog suppression effect of FMCW laser detection baseline
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Fog backscattering can cause false alarm for laser detection, especially multiple scattering of cloud and fog nearby the lidar. By setting up the receiving and transmitting field of view, a close range blind area can be generated to suppress the interference of near cloud and fog. As frequency modulated continuous wave ( FMCW ) laser detection has the advantage of anti-interference, the research on FMCW laser detection has been carried at at home and abroad, but the influence of detection baseline on the effect of FMCW laser detection Has not been studied. The fog and the target echo characteristics are simulated based on the Monte Carlo method. Then the echo spectrum and the calculation value of target distance under different baseline conditions are given. The influence of detection baselines on fog suppression ability of FMCW laser detection is analyzed. The simulation results show that the larger the distance between transmitting and receiving is, the The more prominent the peak of the intermediate frequency signal is, the less obvious the frequency aliasing is. The analysis results conform to the scattering law of cloud and fog on beam propagation, which can provide a basis for target recognition of laser detection and optimal design of Transmitting and receiving field parameters.
Fringe pattern generation of three-dimensional shape measurement based on FPGA
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This paper presents a method about fringe pattern generation of three-dimensional (3D) shape measurement based on field programmable gate array (FPGA). The system hardware is described by logic circuits in Verilog hardware description language (HDL). The system includes signal generation module, signal control module, fringe pattern selection module, video graphics array (VGA) and liquid crystal display (LCD) module. FPGA is used for generating fringe patterns with randomly adjustable frequency, phase and type in the system. Afterward, the fringe pattern is projected onto the object under test by the digital light processing (DLP) projector. The fringe pattern generated by the system is stable and accurate, not affected by the environment and space of measurement. At the same time, it can also make up for the shortcomings of the traditional measurement methods which rely on the computer generating fringe pattern. This method not only cuts down size and cost of the system, but also improves the measurement quality.
Design methods for generating computer hologram based on image quality enhancement
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In order to suppress the speckle noise on holographic display, we present one method for introducing initial phase to desired objects when generating computer hologram. The method considers the relationship of gray value among the adjacent pixels. We perform simulation in order to verify the effect of proposed method. We compare the proposed and traditional methods and conclude that proposed method is better than traditional methods in terms of the quality of reconstructed image. We believe this method can greatly enhance the quality of reconstructed images and it will be widely applied in the holographic field in the future.
The pseudo-diffusive phenomenon in photonic crystals with Dirac cones
Meiqing Liu,
Xiaotong Guo,
Yixuan Wang,
et al.
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Pseudo-diffusive phenomenon is an abnormal transmission phenomenon both in electric system and photonic system which hold conical dispersion relations in their band structures. The phenomenon is: near a Dirac point, the transmittance of the system is inversely proportional to the sample’s thickness as if the material was a disordered medium. It is known that in photonic system, Dirac cones can be classified into three different types, which are standard single Dirac cone, double Dirac cones and Dirac-like cone. Some of them can be found either at the center and the corners of the first Brillouin zone. So it raises the questions that: Do the types of the Dirac cones affect the pseudo-diffusive phenomenon? And further, is there any connection between the pseudo-diffusive phenomenon and the locations of the Dirac cones? Through theoretical investigation, we found that the locations of the Dirac cones play a critical role on the pseudo-diffusive phenomenon. If the Dirac cone is located in the center of the Brillouin zone, the pseudo-diffusive phenomenon doesn't exist at the Dirac frequency. Besides, the shapes of the Dirac cones also affect the pseudo-diffusive phenomenon. The non-conical dispersion band of the Dirac-like cone makes the transmission quite different from linear decrease with the increase of the thickness.
A high-precision and small-volume stepping displacement microplatform for focusing ion beam etching of optical antenna
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To focusing ion beam etching (FIB) machine, the maximum effective processing size in x- and y-direction is still in ~100 micron scale during a single manufacturing cycle, generally. Considering the performances of existing equipments, it is a core operation that a high-precision and small-volume stepping displacement microplatform with a larger manufacturing size of more than that of existing equipments, is constructed effectively for fabricating optical antenna with a size in centimeter scale. The designed setup can be used to conduct a two-dimensional displacement with very high precision of few tens of nanometers for processing sample with structural size scope in centimeter level or even more, is to attach to the working plate of the FIB machine. In this paper, the 80C51 single-chip microcomputer is used as the control setup. Based on the analysis of the three closed-loop DC speed regulation system, the key parameters of the controller are designed according to the dynamic and static performance indicators of the system. Using Matlab's Simulink and Power System toolbox, a three-mode closed-loop DC speed control system for positioning and current generating is built. The model and the key parameter setting of the positioning loop, the speed loop and the current generating loop, are introduced. The simulation model and results of the DC reversible speed control system are given. The simulations verify the model, which can be effectively utilized to correct the parameter setting. It should be noted that the current change rate is suppressed while maintaining a maximum allowable changing rate, so as to make the entire current waveform being closer to the ideal waveform.
Modified constant modulus algorithm based on constellation matching error with variable weight
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In this paper, we propose a modified constant modulus algorithm based on constellation matching error with variable weight (VW-CME-MCMA) for polarization-mode dispersion (PMD) equalization in coherent optical communication system. The new algorithm added a constellation matching error (CME) term to the cost function of the traditional modified constant modulus algorithm (MCMA), considering that the CME term does not provide correct error information in the early stage of algorithmic equalization. In this case, the CME is equivalent to the noise role. Therefore, the new algorithm adaptively adjusts the weight of the CME term according to the error value of the current equalizer output signal. Through the analysis of simulation results, the new algorithm proposed in this paper can achieve faster convergence speed and lower steady-state error.
A weighted clustering algorithm based on node energy for multi-UAV Ad Hoc networks
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In order to solve the problem of endurance of high-speed mobile multi-UAV in Ad Hoc networks with frequent network topology changing, this paper proposes a weighted clustering algorithm based on node energy (EWCA). In this algorithm, we use a multi-parameter weighted clustering algorithm, which improve the node degree difference and node residual energy calculation methods, and study the similarity between the adjacent nodes in terms of speed, direction, etc. The simulation studies the inter-cluster switching rate, the number of nodes and the performance of the minimum lifetime of network node. The results show that, compared with the highest node degree algorithm (HIGHD), adaptive security clustering algorithm (SWCA) and weighted clustering algorithm (WCA), the proposed algorithm can reduce the number of clusters, improve the stability of clustering, and the survival time of drones, and improve the network's endurance.
Tunable multichannel guided-mode resonance photonic crystal filter
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A guided-mode resonance(GMR) filter which can work at multiple tunable frequencies is designed and obtained by using a readily available photonic crystal. The photonic crystal consists of several layers of dielectric rods with different radii in each layer. When light is incident upon this photonic crystal at a small incident angle, guided mode resonance in each rod layer will be excited. At the resonant frequencies, nearly 100% narrow reflection peaks with zero reflection sidebands, an excellent GRM filter, can be obtained. In addition, the resonant frequency of each layer is closely related to the radius of the rod and all the resonances of the whole structure almost don't interact with each other. Therefore, by adjusting the radii of the rods in each layer, the operating frequencies of the filter can be freely tuned both individually and simultaneously, a perfect tunable multichannel GMR photonic crystal filter is obtained. This optical device has apparent advantages, simple structure, small and compact size, easy fabrication and integration. Therefore, it has great application potential in modern optical network.
Time offset measurement of 100 km long fiber link with dual-comb linear optical sampling
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We demonstrate a time-offset measurement with sub-picosecond resolution over l00 km long fiber using asynchronized dual-comb linear optical sampling.
Leakage detection and location analysis of tap water pipe based on distributed optical fiber temperature measurement
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A distributed optical fiber temperature measurement system based on Raman scatter and optical time domain reflecting (OTDR) was used to detect and locate the leakage of water pipe. Firstly, the temperature resolution of the system and the temperature difference at the leakage point were analyzed in the paper. Secondly, the lengths of 200m sensing fiber was used to locate the leakage of water pipe, and the detection signal was processed by accumulative averaging and wavelet transform. Finally, the location of pipe leakage was identified by comparing threshold signals and leakage signals. The experimental results show that the distributed fiber optic temperature system operation was stable and can identify the water pipe leakage.The system can leak location and the positioning error was less than or equal to 1m.
Air-cooling 60 W Tm:fiber laser and its applications on transparent plastics processing
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We demonstrate the first 60 W Tm3+-doped all-fiber laser with single-mode 10/130 fiber and compact air-cooling thermal management way at 1945 nm. The overall optical conversion efficiency reaches 42.2%. High laser power stability of <1.5% is obtained during a continuous test time of >15 hours. The spectra linewidth at maximum output is evaluated as only 0.19 nm. Meanwhile, its direct bonding applications on kinds of transparent plastics are presented.
Optical phase characterization of neuron firing with periodic stimulation
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A neuron is the basic unit of the structure and function of the biological nervous system. The detection of neuronal firing is developed rapidly in recent years. However, the cell activity may be affected by most of the technologies. Considering that the concentration of calcium ion in the cell body plays a key role in modulating neuronal firing activity and the solution refractive index is closely related to its concentration, the optical phase information of a neuron is employed in this paper to describe its firing rhythm with a label-free approach. Based on the associated optical parameters, a neuron model with soma and synapses is presented. Due to the phase information of a sample is actually a set of spatial distributed data, the edge detection is performed with a gradient operator to determine the sampling point of phase data for dynamic monitoring. Since the calcium in neurons mainly exist in neuron cytoplasm, Cacl2 solution is used to simulate the liquid environment in neuron cytoplasm, and the relationship between the refractive index of the solution and the change of the ion concentration is measured through experiments. To demonstrate the phase variation during neuron firing, we take periodic change in calcium concentration in the neuron plasma as an example by simulation. According to the above result, the similar periodic variation of refractive index is be obtained by numerical calculation, as well as that of phase value at the sampling point. From the phase distribution, the variation of phase value can be observed clearly. This work could provide the basis for the label-free detection and characterization of neuron firing.
Thin films of high reflectivity for efficient radiative cooling
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Passive radiative cooling dissipates heat from Earth into outer space through the atmospheric transparency window (8–13 μm). This technique can be useful for applications in passive building cooling, thermal photovoltaic energy conversion, renewable energy harvesting and passive refrigeration in arid regions. Here we propose a novel design of thermal radiative structure based on one-dimensional (1-D) photonic films which reflects 98.28% of solar radiation while emitting remarkably and selectively in the atmospheric transparency window, where the peak emission reaches 99.5%. Samples are characterized experimentally by using a Fourier transform infrared spectrometer and the experimental results match well with the theoretical ones. The structure can theoretically achieve a temperature reduction of about 50.3 °C from the ambient air temperature without solar radiation and non-radiative heat transfer. Under dry air conditions and assuming non-radiative heat transfer coefficient hc=6.9 Wm-2K-1, it can theoretically achieve a temperature reduction of about 6 °C under direct solar radiation (AM1.5). Without the presence of non-radiative heat transfer, it can cool down 36.3 °C below the ambient air temperature at daytime radiative cooling.
Study on calibration method of field spectrometer measurement
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Field spectrometer plays a significant role in geological survey, agriculture, vegetation remote sensing, marine remote sensing and environmental monitoring. In the measurement of field spectrometer, the calibration algorithm and correlation processing of spectrometer are the key points and the research hotspots. In this paper, the methods of third-order fitting, linear fitting, polynomial fitting and normalization, respectively, to achieve the field of the spectrometer wavelength calibration and deal with the nonlinear correction algorithm. With the help of the processing ability of big data of the PC, a series of calibration algorithms and related processing functions of wavelength calibration and nonlinear correction spectrometer are designed. Experimental results show that the field in the spectrometer calibration accuracy, accurate to 0.3 nm wavelength measurement, nonlinear fitting precision to 1.029, these algorithms in field spectrometer with actual application, good results were achieved.
LIBS spectra automatic baseline correction method based on iterative morphometric weighted penalized least squares
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Laser induced breakdown spectroscopy (LIBS) is an analytical technique that has received increasing attention due to many applications. A continuous background will cause baseline drift, which significantly affects spectral analysis. In this paper, an automated baseline correction method based on iterative morphological operations and weighted penalized least squares method is used for LIBS spectral baseline correction. This method can correct the estimated baseline. Experiments on simulated spectra and actual laser-induced breakdown of stainless steel sample LIBS data show that this method is accurate and flexible when used for LIBS spectral baseline correction.
Ultrahigh extinction-ratio circular polarization analyzer with chiral plasmonic lens
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A chiral plasmonic lens (CPL) suitable for circular polarization analyzer is designed and numerically investigated. It consists of two arrays of rectangular nanoslits milled into a gold film along Archimedes spirals. We demonstrate both theoretically and numerically that the designed structure can convert an incident circularly polarized light beam with prescribed chirality into a Bessel-like distributed focus, but the circularly polarized one with the opposite chirality cannot be transmitted and focused by the same CPL due to the alternative chirality. Further, three-dimensional finite-difference time-domain (FDTD) simulations show that an ultrahigh extinction ratio up to ten thousands of the CPL is numerically achieved with a device less than 10 λspp, which is two orders higher than that of a conventional plasmonic circularization analyzer with single Archimedes-spiral groove. The designed structure can be widely used in miniature polarimeter and detection of spin angular momentum.
Broad FSR and high sensitivity refractive index sensor using photonic crystal nanobeam cavity with composite lattice cells
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We propose a broad FSR and high sensitivity refractive index (RI) sensor by using a composite lattice cells based photonic crystal nanobeam cavity (CLC-PCNC). Due to the special structure of the proposed CLC, cavities with free spectra ranges (FSRs) more than 90nm meanwhile with quality factor (Q) values above 5×104 are obtained. Besides, the optical overlap integrals of nearly 30% are achieved for both of the fundamental and the first order dielectric mode of the cavity, quantitatively demonstrating strong interaction between optical and matter, resulting in high sensitivities for RI sensing. Simulation results show that sensitivities of 390.9 nm/RIU and 413.6 nm/RIU, and detection limits of 7.6×10-6 RIU and 7.2×10-6 RIU, are achieved for the fundamental and the first order dielectric mode, respectively. Furthermore, ultra-compact size of only about 220 nm × 550 nm × 10 μm (height × width × length) of the cavity is realized. Therefore, due to the remarkable performances, the proposed sensor shows great potential in realizing applications such as high integration large-scale on-chip sensing and multi-function detection in the future.
A novel demodulation of chirped fiber Bragg gratings using optical power measurement
Hao Zhang
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Demodulation is a bottleneck of application of chirped fiber Bragg gratings (CFBG). A novel demodulation of CFBGs based on optical power measurement is presented in the paper to replace traditional demodulation based on optical spectrum analyzer (OSA). The method uses two CFBGs of which the reflection spectra partially overlap each other. The wavelength shift of CFBG can be related to the optical power of overlap spectra of the two CFBGs. Therefore, the demodulation of CFBG can be realized by optical power measurement. The advantages of the demodulation method include simple structure, high flexibility, and low cost.
GPU based real-time enhancement of high resolution image
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Curvature filter and gradient transform based image enhancement algorithm can effectively suppress noises and enhance image edges. However, it is very hard to be carried out in real time due to the large computing load. To address this problem, a GPU based parallel implementation is proposed in this paper. First, aiming at the characteristics of the algorithm, a numerical implementation method based on central-difference is proposed. Then a domain decomposition scheme is utilized in parallel Gaussian curvature filter to remove the dependence of neighboring pixels and guarantee convergence. Finally, we make the multiprocessor wrap occupancy reach 100% by optimizing the thread grid and register usage. Experimental results demonstrate that our parallel method runs 200-300 times faster than CPU serial method with real time processing of 4096×4096 resolution image, which indicates a great potential for application.
Derivative method for fast phase imaging in simultaneous dual-wavelength off-axis phase-shifting interferometry
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Dual-wavelength interferometry is one of the most effective technique in optical metrology and phase imaging by virtue of its unique advantages. In this paper, a fast derivative method for phase extraction is proposed to improve the imaging efficiency in simultaneous dual-wavelength interferometry. In this algorithm, only three off-axis wavelength-multiplexed phase-shifted interferograms are required. And only by calculating the difference between the first interferogram and other interferogram and calculating its first-order derivative, the wrapped phase of each single-wavelength can be obtained. Subsequently, the continuous phase at a synthetic wavelength can be determined freeing from the complex unwrapping procedure. Moreover, the thickness can also be obtained from the phase. Simulation results show that this method is effective and demonstrate its performance of faster computing speed and high accuracy.
Study on ablation threshold of fused silica glass by femtosecond laser induced backside wet etching
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This article presents the research on the ablation threshold of fused silica glass processed by femtosecond laser in different environments, such as air, distilled water, and pure alcohol solution. At present, studies on ultra-short pulse lasers on materials mainly focus on the ablation threshold and material removal mechanism of specific materials. By analyzing the ablation threshold of the material, the laser processing efficiency can be greatly improved. Therefore, this paper mainly studied the material removal mechanism of fused silica and calculated the ablation threshold of fused silica in different environments. By analyzing the experimental results, we found that the surface-ablation threshold of fused silica glass can be relatively reduced in liquid environment relative to the air environment. Compared with distilled water, the surface-ablation threshold in pure alcohol solution can be significantly decreased. Besides, by comparing the results, the surface morphology quality in the liquid solutions is superior to the air. The research content of this article has given a certain theoretical guidance for the processing of transparent materials and laid a certain foundation for subsequent research work.
High-repetition-rate cavity dumped Yb:YAG thin disk laser
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High-peak-power, short-pulse-width cavity dumped Yb:YAG thin disk laser is demonstrated. A constant pulse width of 20.3 ns±0.2 ns is achieved within the frequency region between 10 kHz to 100 kHz. The output peak power achieves 109.8 kW, 37.8 kW and 20.9 kW respectively at 10 kHz, 50 kHz and 100kHz.
Non-scanning 3D endoscopic imaging through a multimode optical fiber based on monochromatic transmission matrix
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Imaging by a multimode optical fiber (MMF) has attracted much attention because single MMF could be used as a thinner endoscope probe than traditional ones. One essential feature of the MMF endoscope probe is its endoscopic imaging mode. It is well known that clearly imaging through an MMF is somewhat difficult, this is due to the fact that light waves transmitting in an MMF will be modulated randomly because of the mode dispersion in it. What’s worse, for endoscopic imaging case, such a random modulation effect will be suffered twice: on the way in for illuminating and on the way out for imaging. In this paper, by measuring the monochromatic transmission matrix (TM) of the MMF in the case of working under the endoscopic imaging mode, we realize an MMF-based round-trip imaging through phaseshifting interferometry measurements by use of a spatial light modulator. Experimental results indicate that the images of objects can be effectively recovered using the presented approach. It is found that this approach has several advantages. Firstly, it avoids scanning objects, thus leading to quickly imaging; Secondly, it can also recover 3D information of the objects from seriously distorted optical fields emerging from the MMF. We predict that this approach might be applied for single-fiber rapid 3D endoscopic imaging.
Separation of variables based method for fast calculation of imaging system in lithographic tools
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For lithographic tools, the forward model of imaging system is repeated many times in the inverse optimization algorithm of optical proximity correction (OPC). Fast and accurate imaging simulation is highly desirable as one of the most critical components in the forward modeling simulations. We have focused on investigating the physical properties of optical imaging in lithography and introduced the method of separation of variables in Mathematical Physics as the fundamental theory to deal with a wide range of process variables. We proposed a rigorous methodology from first principles to speed up image simulations. The proposed imaging formula can be rearranged by two parts, one with only variables, while the remaining part independent with the variables. Simulations for a variety of different process variables confirmed that the proposed method yields a superior quality of image with an accuracy of 10-3 and superior performance of speed. Therefore, the proposed method provides a novel theory and practical means for OPC and other resolution enhancement technologies (RETs) in optical lithography.
Numerical investigation of scaling of diode pumped metastable rare-gas laser end-pumped, MOPA
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As a novel cw hybrid laser, the lasing wavelengths lie in the near-IR range and for in the transparency window of the terrestrial atmosphere, diode pumped metastable rare gas lasers (DPRGLs) can be considered as a beam conversion system that produces a high-quality laser beam by passing a diode laser with poor beam quality through the rare gases medium at room temperature. In this paper, a numerical model is set up to describe the kinetic processes and the laser amplification, based the five-level structure, in DPRGL amplifier (DPRGA) system. Influences of the pump power and the cell length on the output laser are simulated and discussed. Such a master oscillator power amplifier (MOPA) system is very promising in achieving high output power for low power DPRGL radiation.
Effect of temperature on conversion characteristics of segmented PPLN based wavelength converter
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In this paper, we investigate the influence of temperature changes on the grating periods of periodically poled lithium niobate (PPLN) with segmented grating structure. Furthermore, the effect of temperature on the conversion performance of segmented gratings based wavelength converter is also studied. Giving the basic constraints of the wavelength conversion characteristics, the grating periods of the segmented gratings at different temperatures is collected when the constraint conditions are met. Then, three mathematical equations are achieved by analyzing the collected data to calculate the optimal grating periods for different temperatures. Broad bandwidth with flat response can be obtained by using these optimal grating periods. Finally, comparison between the designed segmented gratings- and uniform grating-based wavelength converters is carried out. The results show that, for the same temperature, the wavelength converter with segmented gratings has broader bandwidth and more flat conversion efficiency than that with uniform grating.
A dual-wavelength phase retrieval method under the interference microscopy imaging
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Dual-wavelength digital holographic microscopy technique has many important applications in the imaging of biological cells. It has some significant advantages, such as the large measurement range and no phase unwrapping procedures. However, the multi-steps image is required in synchronous interference microscopy, it is not suitable to perform real-time dynamic imaging of samples. In this paper, in order to meet the research and clinical application of dynamic imaging of living cells, a phase recovery algorithm is proposed in dual-wavelength interference and one-step microscopic imaging. This algorithm is on the basis of the principle of the digital holographic off-axis synchronous microscopy image. In this algorithm, only by means of Fourier transform, filtering, frequency-shifting operations, inverse Fourier transform to the dual-wavelength off-axis microscopic interferogram, the continuous phase of the sample can be calculated. Simulation result of the lymphocyte shows that this method is feasible, and the error analysis suggests that it has good accuracy. This approach is free of phase unwrapping, and has no the calculation of the phase shift and no the multi-step imaging. It can recover the phase distribution only from one dual-wavelength interferogram. So it has a high potential application for the technology development, and can be applied to accurate dynamic imaging of biological cells and tissues.
Liquid-crystal microlens arrays driven addressably by electric-scanning signals
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Approaches for realizing a small scale tunable liquid-crystal microlens array (LCMLA) with several independent driving channels of applying voltage signal has been investigated in recent year. However, current requirements based on electrically tuning focus function are further increasing array scale of LCMLA and continuously improving driving efficiency of electric-signal setup so as to acquire more optical information of objects. The conventional point-to-point electrically driving (PTPED) method, which has disadvantages such as high power dissipation, lots of external wirings connections, and complicated electric-structure matching, cannot be used to accomplish a real-time independent driving control of arbitrary electrode end in a patterned electrode array of a LCMLA. In this paper, an addressably electric-scanning driving (ESD) approach for a 4×4 zoned LCMLA with sixteen electrode zone divided so as to reduce the number of driving signal lines, is proposed. Simultaneously, key functions such as the amplitude and frequency of a square-wave voltage signal for driving arbitrary electrode with needed RMS voltage value, which can be programmable processed so as to independently control zoned electrodes, can be effectively achieved. The principle of ESD of LCMLA, the simulation and design of hardware circuit, and the fabrication of ESD device are presented. According to our experiences in LCMLA, the ESD approach will exhibit possibility for construction and application of large-scale LCMLA. Besides, scene scanning automatically and three-dimension object reconstruction based on addressable LCMAL with multi-focuses is also predicted.
Measurement and compensation for the chromatic aberration of SG-II 5PW laser system
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Pulse time delay (PTD) and defocus are mainly introduced by transmitted-based large-aperture beam expander systems in ultrashort high power laser systems due to chromatic aberration, which can significantly reduce the focal-spot intensity by spatially enlarge the spot size as well as temporally distort the pulse profile. In this paper we investigate the chromatic aberration and measure how it deteriorate the focal spot size in SG-II 5PW ultrashort laser system. In addition, we propose and design a simple chromatic aberration pre-compensation scheme based on combination of aspherical lens and spherical mirrors. The simulation results indicate that both PTD and defocus dispersion can nearly be fully compensated by applying this compensation scheme with proper alignment in the system without introducing other kinds of wave-front aberrations.
Hugely tunable circular dichroism based on phase-change planar chiral metamaterials
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Circular dichroism (CD), different absorption of RCP and LCP waves, can be strongly enhanced in chiral metamaterials. CD spectrum is very meaningful feature in both biology and chemistry to probe the conformational state. In this paper, planar chiral metamaterials (PCM) comprising of a tri-layer metal/phase-change material (VO2) /metal sandwich and conjugated gammadions are both studied theoretically by using finite-difference time-domain (FDTD) method. And a wide tuning range of CD is obtained by changing temperature of VO2. Particle swarm optimization (PSO) algorithm is used to optimize the geometric parameters of PCM structures. A large value of circular dichroism in excess of 40% is presented in dielectric PCM, but CD drop down to 16% in the metallic PCM at λ=1.18μm. We also analyze the distribution of current modes, electric and magnetic fields at the resonant frequency to account for the above results.
Using blob to analyze image processing method to achieve precision detection of IFU optical fiber microplate
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Aiming at the problems existing in the detection of high precision optical devices, and combining with the market demand, this paper develops a high precision optical element surface detection system, based on Blob analysis of machine vision to detect the surface quality of high-precision optical components fully automatically and constantly. The system consists of four parts: automatic photography, image processing, image mosaic and surface data statistics. While improving the detection efficiency and reducing the cost of detection, the accuracy and reliability of high precision optical elements detection are improved. The measurement accuracy reaches the μm degree. It has a good detection performance.
Computer-aided infrared camouflage effectiveness evaluation method based on image saliency
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This paper reports on a new computer-aided method for the infrared camouflage effectiveness evaluation of a target based on its image saliency. The image saliency of a target was computed according to its background-related features, including intensity, contrast, gradient and orientation features in one real infrared image. On the basis of the former saliency value, the camouflage effectiveness value of a target was calculated quantitatively. The results clearly indicated that the target without infrared camouflage had a low camouflage effectiveness value, while a target with good infrared camouflage (the camouflage pattern patches of the target matched well with the background) had a high camouflage effectiveness value, which proved that this method could not only reflect the infrared camouflage effectiveness of a target in the corresponding background actually but also help us differentiate the camouflage quality of different materials quantitatively. This method should be of importance for us to evaluate the infrared camouflage effectiveness of a target more quickly and objectively with the help of computers, instead of human observations.
Wave-transition contribution to the Faraday effect and Verdet constant
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Verdet constant is one of the key parameters to characterize the material's magneto-optical properties, along with the wavelength and temperature dependence. In order to thoroughly analyze the influence mechanisms of the incident wavelength and temperature on the Verdet constant as well as uncover its essence, both advantages and disadvantages of the classical electronic dynamics theory and quantum theory on account of basic theories and test data are discussed. By exploring the physical essences and models of the two theories, their significant associations between the medium’s polarization intensity and the molecular polarizability are determined. The former decides the medium’s permittivity and refractivity, and in turn, influences the Faraday rotation angle and Verdet constant. It should be noted that the polarizability includes not only those transition dipole moments from the electrons’ transitions between different states, but also the inductive dipole moments which is due to the non-transition electron cloud being polarized. Hence, a hypothesis is proposed which suggests that the Faraday effect results from the combination of various factors. Accordingly, a theory of wave-transition contribution to the Verdet constant is deduced. Taking the typical diamagnetic material ZF1 and the typical paramagnetic material TGG as examples, the influences of the incident wavelength and the temperature on the Verdet constant are analyzed. The deduced theory together with the corresponding models is tested and verified by analyzing the relevant parameters and the test data. The results show that the wave-transition contribution theory and its models are superior in the aspect of precisely describing the material's Verdet constant.
A modulation classification method based on deformable convolutional neural networks for broadband satellite communication systems
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In order to solve the problem of broadband satellite modulation signal with SNR fluctuation of complex channel and various modulation signal recognizing, we propose a Deformable Convolutional Neural Networks (DCNN) classification model based on broadband satellite communication systems. In our algorithm, we propose a deformable convolution kernel, which only need to calculate the 2/3 pixel convoluting. Our algorithm not only can be used to reduce the complexity and improve the robustness, but also used to improve the accuracy. We simulate the accuracy and the complexity of the algorithm among the four neural network models of DCNN, VGG, AlexNet and ResNet. The results show that the design of the DCNN model has high recognition rate and low algorithm complexity. Then we simulate the DCNN network in variable signal-to-noise of BPSK, QPSK, 8PSK, 16APSK, 32APSK, 16QAM, 32QAM and 64QAM commonly used satellite modulation signal classification and complex channel conditions, and training the four basic modulation signal used to identify other modulation signals. The results show that the DCNN model not only can be used to maintain a high recognition rate of the modulated signal, but also used to reduce the complexity of the algorithm and improves the robustness of the algorithm.
A multi-regions electrically tunable liquid crystal microlens array for extending the depth of field
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Depth of field (DOF), which is also called the effective focusing range, is a basic parameter for imaging systems. Usually, after the focusing, a clear image acceptable within a certain range before and after the focus is expressed. The length of this range is called the DOF. According to the definition of DOF, for a lens with a fixed focal length, the image formed by an object outside the depth of field is blurred, which means that sufficient information will not be obtained. For conventional imaging systems, a relatively large DOF can be achieved by reducing the aperture, but this will reduce the amount of incident light, thereby reducing the system imaging quality. In this paper, we propose a multi-regions electrically tunable liquid crystal microlens array (LCMLA), which is fabricated according to traditional photolithography and standard microelectronic techniques and divided into three sub-regions with three independent electrodes. It can apply different voltages on different sub-regions to obtain different DOF corresponding to them. Based on this, it will be possible to clearly image objects in field of view (FOV) that are outside the depth of field of one or more sub-regions at the same time, which means an extension of the DOF.
A novel frequency-locked multicarrier generator based on a dual-electrode Mach-Zehnder modulator
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A novel frequency-locked multicarrier generator(MCG) by utilizing a dual-electrode Mach-Zehnder modulator (DE-MZM) and a phase modulator has been proposed and analyzed theoretically. The transfer function and output properties of the proposed multicarrier generator have been derived. Simulation results show that the DE-MZM-based MCG has the ability to generate multiple frequency-locked carriers with acceptable flatness.
Temperature sensing based on phase-to-intensity modulation conversion in fiber Bragg grating
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In this paper, a method of temperature sensing based on microwave signal generation with fiber Bragg grating (FBG) as a frequency discriminator is proposed and experimentally demonstrated. According to the proposed approach, the optical carrier frequency is placed at the slope of the phase response of the FBG. The measure and to the phase of microwave signal generated by the frequency discriminator is mapped through an electrical spectrum analyzer. The proposal can describe the change in the flat area of the amplitude response, which improves the sensing resolution of the temperature near the center wavelength. Higher precision can be distinguished from the slope of the phase response. A result that the sensor responds to temperature with a sensitivity of 5.2dB/°C is achieved.
Modeling and simulation of optical micro-nano-antenna for THz radiation
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Generally optical micro-nano-antenna can be used to modulate lightwaves in the sub-wavelength scale, which is a hot and difficult research issue. Patterned metal nano-antenna array can be utilized to stimulate intense surface plasmon polaritons (SPPs), so as to realize sub-wavelength focusing by breaking through diffractive limit, and thus remarkably improving THz imaging efficiency. In this article, firstly, based on SPPs, the Drude dispersion model for metallic film is analyzed, and the dispersion relations and excitation modes of the SPPs are discussed, and the numerical analysis methods of the metallic micro-nano-antenna are also presented including a time-domain finite integral method and a frequency-domain finite element method. According to related literature, the key optical micro-nano-antenna unit is modeled, and a metasurface formed by etching a gold thin film on a silicon substrate is designed. Through regulating parameters including the number and size of the openings and the line width, the SPP excitation in THz band is studied. Using finite element and adaptive mesh division method, the common electromagnetic properties such as transmission intensity and electric field distribution are simulated and analyzed. The simulations show that the optical micro-nano-antenna element can resonantly induct terahertz wave, and demonstrate a resonant electric-field at the aperture gap, which will move towards high frequencies end as increasing the gap size or line width, so as to lay a concrete foundation for continuously fabrication THz-SPPs devices.
Modeling and simulation of electromodulation imaging spectrum based on a MEMS-FP array with a high filling-factor
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The Fabry-Perot interferometer (FP) can be used as a kind of filter for obtaining spectral information of targets in several wavelength ranges such as in the visible or infrared regions. Micro-electro-mechanical systems (MEMS) are generally micro-structures that integrate micro-sensors for converting incident microbeams into arrayed electronic signals and micro-actuators. The MEMS-FP filter constructed by combining the MEMS and FP functions, can be further integrated into a chip-level imaging spectrometer to achieve spectral imaging operation. In our design, the MEMS-FP filter is also mounted a liquid-crystal microlens array with a high filling-factor. The key micro-bridges of each MEMS-FP unit are modeled and simulated in this paper. We have designed two types of supporting structures and simulated them with the simulation software COMSOL Multiphysics 5.2. The key factors include tuning range, filling-factor, and parallelism of the bridges. After calculating and analyzing, we found that the tuning range can be optimized by changing the thickness of the micro-bridge and the arm width of the cantilever beam. The filling-factor is already increased by geometry design. The parallelism of the bridge in the two micro-structures differs greatly, which is related to the shape of the bridge itself. According to the simulations, a tuning range of 160 nm has been achieved in the visible and near-infrared wavelength range, with a maximum filling-factor of more than ~80%.
Measurement of the coherence of multi-transverse-mode optical field based on liquid crystal spatial light modulator
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In this paper, the fast measurement of the coherence of the multi-transverse-mode optical field is realized by using the intensity type of liquid crystal spatial light modulator (LC-SLM). Using the characteristic and advantage of the LC-SLM which can change the location of the light hole quickly and easily, and basing on the method of dual-hole interference, we divided the 650nm multi-transverse-modes laser spot into 4×4 points, and performed a quick scan with pairs of double holes of diameter 150μm. The contrast ratio of the interference patterns is computed by a self-made image processing software, and the coherence degree between the two points can be obtained. The experimental results show that the measurement system can accurately measure the coherence of multi-transverse-mode optical field within 10 seconds, which providing guideline for the further mode decomposition and beam control of multi-transverse-mode optical field.
Enhancement for high-luminance objects by a false-color-depth method
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When analyzing high-luminance objects such as plasma and high-temperature fireballs, in order to enhance the image of highlight targets, a false-color-depth method, similar to the reduction of the color depth, is proposed. Multiple false-color-depth figures with low color depth were acquired by this method and then multiply these low-color-depth figures to get a final figure. The processed figures, as a result, show that the low-brightness background of the image can be effectively attenuated by this simple algorithm, and the preliminary gray-level image segmentation can be performed on the high-luminance target.
Research on spectral calibration of the hyperspectral irradiance-meter in near-infrared band (900-1700nm)
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With regard to the visible and near-infrared hyperspectral irradiance-meter developed by ourselves, the theories and methods of spectral calibration are discussed.The visible and near-infrared hyperspectral irradiance-meter is composed of three optical modules: the visible spectral module(400-1000nm)(VIS), the near-infrared spectral module(900- 1700nm)(NIR), the short-wave-infrared spectral module(1600-2500nm)(SWIR).The detection units use flat-field concave grating to diffract and focus different wavelengths, use the linear array detector to detect signals.For the NIR spectral module(900-1700nm), two spectral calibration methods are adopted: argon lamp calibration and wavelength standard panel calibration.The theories of the two spectral calibration methods are expounded, and the corresponding calibration steps are designed.When the argon lamp or the wavelength standard panel is used in the laboratory to calibrate the NIR spectral module(900-1700nm), the correspondence between the response and the pixel of linear array detector is obtained through diffracting and focusing different wavelengths by the flat-field concave grating. Depending on the characteristic spectrum of the argon lamp or the wavelength standard panel, the spectral calibration equation in the range of 900-1700nm (the NIR spectral module) is derived through data polynomial fitting. The calibration results show that the fitting errors of the two methods are less than 0.45nm and 1 nm respectively, and the spectral calibration uncertainties are better than 0.5nm and 1.2 nm respectively.The two calibration methods verify that the design of the instrument’s spectral module is rational, and provide a meaningful reference for various spectral calibration methods of the near-infrared spectral module.
Application of wavelet threshold denoising in PMD measurement by fixed analyzer method
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In order to eliminate the error introduced by noise from fixed analyzer method when measuring polarization mode dispersion of optical fiber and improve the accuracy of the polarization mode dispersion measurement system, a novel denoising approach based on wavelet threshold denoising is proposed in this paper. This paper presents the algorithm flow chart based on wavelet threshold denoising and discusses the selection principles of wavelet threshold, wavelet threshold function, mother wavelet and the number of wavelet decomposition layers. We built an experimental platform and compare the measurement results with Fourier transform algorithm and the commercial polarization mode dispersion measurement instrument. Experimental results show that the proposed wavelet threshold denoising method can effectively reduce impact of noise on the measurement results effectively, which is suitable for different types and lengths of test fiber samples. Taking the commercial instrument as the standard reference, the maximum error of the measurement result of this scheme is 2.27%, which improves the accuracy significantly of the polarization mode dispersion measurement results measure by the fixed analyzer.
Depolarization degree of picosecond radially polarized beam induced by non-radially symmetrical pumping during power amplification
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The effect of the gain medium planar shear stress, induced by non-radially symmetrical pumping during power amplification process, on the depolarization of radially polarized beam was analyzed in detail. For radially polarized beam, theoretical simulation had showed that the non-radial distribution of planar shear stress led to the different depolarization in different polarization directions, that the depolarization of the direction of 45° and 135° is five times more serious than that of 0° and 90°. In the following experiment, the radially polarized seed beam with a repetition rate of 1 kHz, an average power of 5 W and a pulse width of 100 ps was single-propagating double-rod Nd:YAG laser amplifier. Each rod was surrounded by three diode-pumped arrays with an angle of 120°. During the amplification process, the depolarization degree of radially polarized beam was 6.73%, which was obtained by measuring the difference between the power of the two beams transmitted and reflected by the analyzer TFP. The power of amplified radially polarized beam was 15.17 W with the purity of 89.3% and M2 of 3.95.
Study on cascaded tunable DBR semiconductor laser with wide tuning range and fast switching speed
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A compact cascaded tunable distributed Bragg reflection (DBR) semiconductor laser is proposed and simulated. Each laser section (LS) is formed by two passive adjacent grating sections (GSs) with slightly different Bragg wavelengths and an active section (AS) between them. A step-wise grating period profile is designed to realize wide range lasing. Since two LSs share a common GS, the total cavity length of the tunable laser is significantly reduced. As an example, a tunable laser with four GSs and three ASs was designed and analyzed, resulting in a continuous tuning range of 13.2 nm. Furthermore, an improved structure with apodized grating in each GS is proposed for good single mode property. The single mode stability and fabrication tolerance are significantly improved. Particularly, this structure based lasers has a fast switching speed of about 5ns. The proposed structure would benefit the practical applications to the low cost tunable lasers in wavelength division multiplexing (WDM) systems.
High-power VCSEL side pumped 2° wedge angle Nd:YAG repetition rate 1kHz four-pulses sequence picosecond regenerative amplifier
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A four-pulses sequence picosecond 1064nm regenerative amplifier system with repetition rate of 1 kHz are obtained, which with the average power of 9.2 W and beam quality M2 factor of 1.2. The Nd: YAG crystal with wedge angle of 2° and size of Φ 4×63 mm is adopted in the regenerative amplifier and around by three VCSEL pumping arrays with an angle of 120°. A laser diode (LD) pumped Nd: YVO4 crystal SESAM mode-locked seed laser is broadened from 20 to 260 ps by double-pass Volume Bragg Gratings and divided into equal amplitudes four-pulse sequence with the pulse spacing of 1ns by beam splitter mirrors. The four-pulse sequence enters the regenerative amplifier in order and the power is amplified from 0.68 to 9.5 W.
A simple wideband digital predistortion system based on improved Powell algorithm
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In order to solve the analog-to-digital converter (ADC) sampling rate in the traditional digital predistortion (DPD) system must be several times the bandwidth of the original signal to cover the out-of-band intermodulation components caused by nonlinear radio frequency power amplifiers (PA), lowcost ADC cannot meet today's demand problems. This paper proposes a robust iterative DPD coefficient extraction algorithm based on Powell algorithm and random demodulation. This method applies an improved Powell algorithm to a DPD parameter extraction system. The simulation studies the linearization performance of the system. The results show that when the system feedback bandwidth is equal to the original signal bandwidth, satisfactory linearization performance can be obtained. In addition, different from LM algorithm, Powell algorithm does not require partial derivatives of the estimated parameters, the system is simplified.
Femtosecond laser cutting ultra thin fused silica
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Cutting of ultra thin fused silica sheets is a significant technological challenge because of these materials’ brittleness and high ablation threshold. Femtosecond laser offer a great prospect for meeting this challenge. In this paper, femtosecond laser with a central wavelength of 1030 nm, a pulse duration 230 fs ablation process for cutting fused silica sheets of thickness 100 μm. To improve cutting quality and efficiency, the experiments through optimization of laser processing parameters, including the laser energy, repetition rate and scanning speed, were carried out. And a two-step processing method was proposed for improving the quality of cross-section surface. According to experimental results, the edge along the edges without chipping and smooth cross-section surface were achieved by this method.
Circular optical phased array for 360° constant amplitude scanning
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Optical phased arrays (OPAs) are widely used in many applications to realize high-speed optical beam scanning. At present OPAs often suffer from limited scanning range. Here we propose a circular optical phased array (COPA) based on silicon photonics platform. According to our simulations, by positioning the OPA units in a circle and adopting a specific phase distribution, the COPA can realize 360° constant amplitude scanning. In addition, the design of the disk grating coupler, which is the key device of the COPA, is presented. The COPA is believed to have great potential for applications where a wide scanning range is mandatory.
Monitoring of fiber grating refractive index modulation
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In order to design and fabricate high-performance fiber gratings and distributed feedback fiber lasers, the monitoring of AC and DC components of the core refractive index modulation during grating engraving was studied. Based on the Bragg equation and the coupled mode theory, the average variation and fringe visibility of the core refractive index modulation were calculated by monitoring the grating center wavelength and transmission spectrum depth. The grating engraving experiment of boron-germanium co-doped fiber, germanium-doped fiber, and erbium-doped photosensitive fiber was carried out and their refractive index modulation data was obtained. Experiment also showed that the larger pulse energy would make the average variation of core refractive index modulation increases and the fringe visibility decreases.
High sensitivity temperature sensor based on packaged microdroplet whispering gallery mode resonator
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We experimentally demonstrate a high sensitivity temperature sensor based on packaged microdroplet whispering gallery mode (WGM) resonator. Fabrication process of the packaged microdroplet resonator is easy and controllable. The sensitivity and the electric field intensity distribution of different radial modes are calculated and analyzed by Mie theory. The measured temperature sensitivity is over 200 pm/ °C, due to the mode distribution of microdroplet resonator and high thermo-optic coefficient of dimethyl sulfoxide (DMSO). The proposed packaged microdroplet resonator has the superiority in the high sensitivity and robust property, which exhibit good potential in regards to future integrated photonic devices based sensors.
Measurement of response bandwidth of photoelectric detector with low cutoff frequency
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The response bandwidth is an important parameter to describe the frequency response characteristics of photoelectric detector. It characterizes the response capability of photoelectric detector for different modulated optical signals. The research is based on measurement of response bandwidth of photoelectric detector for acousto-optic modulation technology. Laser power is modulated, and photoelectric detector is used to detect modulated laser and record output voltage. Therefore, the response bandwidth of photoelectric detector can be determined through analysis. Such method is easy to operate and facilitates measuring the response bandwidth of photoelectric detector with low cutoff frequency.
Experimental study of static calibration based on atomic- emission double spectrum line temperature measuring
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Based on the double line of atomic emission temperature measurement technology, combined with storage measurement technology, the photoelectric thermometer was designed by using Y-type fiber, narrow band filter, silicon photomultiplier tube (SiPM). Record the temperature value measured by the photo thermometer and the temperature value displayed on the LCDpanel of the chamber furnace, and obtain the static sensitivity coefficient K by the least squares method. The temperature indicated by the high-temperature box furnace is used as the standard temperature value. A static calibration system is built. The temperature of the heated copper sheet was measured using a statically calibrated photometric temperature measurement system and compared with the measurement results of the M5 infrared. The experimental results verify the feasibility of temperature measurement system. The research work in this paper has important reference value for the development of temperature measurement technology of atomic emission spectroscopy.
A Brillouin Scattering Spectrum frequency shift extraction based on sparse constrainted cross-correlation iterative model
Wenqing Tang,
Feng Tian,
Hongyan Zhao,
et al.
Show abstract
The Brillouin Optical Time-domain Analysis technology(BOTDA) is one of the hotspots in the optical fiber sensing field, it can measure temperature and strain information along the fiber based on the linear relationship between temperature, strain and Brillouin frequency shift. This technology has high measurement accuracy and long sensing distance. However, the Brillouin scattering signal in BOTDA is very weak and easily affected by external factors. In order to further improve the measurement accuracy and real-time performance of distributed optical fiber sensing system based on Brillouin scattering, this paper proposes a Brillouin scattering spectrum feature extraction scheme based on sparse constrainted cross-correlation iterative algorithm model. Different from the traditional cross-correlation convolution algorithm, this method changes the frequency distribution of the reference Lorenz signal by constructing a constraint model to improve the extraction precision of the Brillouin gain spectrum. In this paper, a 24.4km BOTDA temperature sensing experiment system is built. The experimental results show that compared with the conventional cross-correlation convolution algorithm and Levenberg -Marquardt Lorenz curve fitting algorithm, the accuracy of the Brillouin frequency shift extraction of this method is increased by about 5MHz, and the error of Brillouin frequency shift extraction can be controlled at 1MHz.Besides, the computational complexity of this method is far less than theLevenberg -Marquardt Lorenz curve fitting algorithm. Therefore, the sparse constrainted cross-correlation iterative algorithm proposed in this paper can effectively improve the measurement accuracy and real-time performance of the Brillouin optical sensor system.
Spectrum effect on output characteristics of wireless energy and data hybrid transmission system using a solar panels
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Optical wireless transmission system using a solar cell can receive energy and information simultaneously with single link. Optical spectrum of transmitter is the one of factors in wireless energy and data hybrid transmission system, and optical spectrum effects should be researched. Firstly, the energy and data hybrid transmission system are designed and simulated based on lambert model and equivalent circuit of solar cell. Secondly, a hybrid transmission indoor experimental system is established using a monocrystalline silicon solar cell as a receiver. The frequency response of the solar cell is measured with different date rates and wavelengths. Additionally, the output signal’s amplitude and conversion efficiency of receiver with different wavelengths of transmitters (470nm and 850nm) are observed and measured in the process of energy transmission. What is more, 100 kHz output waveform of the receiver in the process of data transmission is researched and discussed in different intensities and wavelengths. The experimental results show that hybrid transmission of data and energy can be achieved in our indoor system. The energy transmission efficiency and amplitude of the receiver signal with 850 nm LED transmitter is better than those of 470 nm LED transmitter (2.1 times and 1.39 times, relatively) in energy transmission process. Compared to the performance using a 470 nm light source in data transmission process, the waveform contrast of 850nm light source band is better.
Mid-infrared parametric amplification in chalcogenide microstructured fibers
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A two-pump fiber optical parametric amplifier (FOPA) based on the photonic crystal fiber (PCF) with As2S3 background in the mid-infrared (MIR) region is investigated numerically. The genetic algorithms are used to optimize the gain of the FOPA, and the amplifier peak gain, bandwidth and flatness are investigated in detail for the variety of the fiber length, the input signal and pump power. In addition, the comparison of the gain spectra between considering and neglecting the loss of the PCF is given. The results show that the wideband gain spectra with high peak gain can be obtained by using a short length of the PCF with the relatively low pump power, which show the great potential of the FOPA at wavelengths in the MIR region.
Simultaneous dual-wavelength reconstruction based on low rank mixed-state and phase modulation
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We propose a single shot dual-wavelength phase retrieval method based on low rank mixed-state and phase modulation imaging. Both the amplitude and phase of each wavelength can be reconstructed simultaneously from the recorded diffraction pattern. Proof-of-principle experiment was demonstrated to show its capability in solving the crucial problem of measuring the high energy laser beam of multi-wavelength inside the target cabin. Because of the extremely high energy and limited inner space of high vacuum, no other techniques can realize this kind of measurement by now. This novel method provides an efficient way for fundamental and third harmonic wave diagnostics in high power laser systems, including near-field phase and far-field intensity distribution, power distribution, frequency conversion efficiency etc. Because this method only needs a phase plate and a CCD, it can be integrated into a compact device with convenient use.
Research on singular value decomposition denoising algorithm on polarization mode dispersion measurement
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In order to eliminate the noise in the polarization mode dispersion(PMD)measurement system by the fixed analyzer method and improve the measurement accuracy, this paper applies singualr value decomposition(SVD) denoising algorithm to polarization mode dispersion measurement scheme. First, construct Hankel matrix in term of a discrete signal sequence, and it was decomposed into a number of matrixes by singular value. Second, divide singular values into two groups: valid group and noise group and fit the valid signal characteristic curve and the noise characteristic curve. Then, calculate the fitting error, and define the minimal order of fitting error as valid order. Finally, reconstruct the signal. The experiments compare results based on the SVD filtering method, Butterworth filtering method and commercial instruments. The results show that this method is suitable in different types and lengths of fiber. The measurement accuracy was improved obviously.
Investigation on wall thickness ranges using digital radiography for tangential projection technique
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X-ray testing is based on the attenuation of X-rays when passing through matter. Image detectors acquire the X-ray information which is defined by the local penetrated wall thickness of the tested sample. By X-ray absorption in the detector and following read-out and digitization steps a digital image is generated. As detectors a radiographic film and film digitization, a storage phosphor imaging plate and a special Laser scanner (Computer Radiography - CR) or a digital detector array (DDA) can be used. The digital image in the computer can then be further analyzed using many types of image processing. In the presented work the automated evaluation of wall thickness profiles are investigated using a test steel pipe with 9 different wall thicknesses and various X-ray voltages and different filter materials at the tube port and intermediate between object and detector. In this way the influence of different radiation qualities on the accuracy of the automated wall thickness evaluation depending on the penetrated wall thickness of the steel pipe was investigated.
Using multiphoton microscopy to assess pulmonary emphysema in mouse models
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Chronic obstructive pulmonary diseases (COPD) is the fifth leading cause of death worldwide and will be increased in the coming decades. Pulmonary emphysema is one of the hallmarks of COPD. Establishing the animal model of pulmonary emphysema is very important to explore its pathogenesis. Until now, researchers are still having used histological methods to assess whether it is successful to stimulate the emphysema animal model. In this study, we try to use multiphoton microscopy imaging system to assess whether the mouse models obtained the emphysema pathological. The two-photon excited fluorescence (TPEF) signals and second harmonic generation (SHG) signals clearly showed changes in both cellular features and extracellular matrix architecture during different time of emphysema mouse models. With the development of miniaturized multiphoton microscopy, multiphoton microscopy can be used to monitor the developing of pulmonary emphysema in animals in vivo.
Full-field stress measurement based on phase-shifting ptychographic iterative engine
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Stress measurement is significant to evaluate and predict optical behaviour of the birefringence components. The separation of two principal stress components is a difficult problem due to the coupling between them. A new PIE-based stress measurement method is proposed. Combining with the four-step phase-shifting measuring method, the complex amplitude transmittance functions of the sample in different phase-shifting states are reconstructed. Then the quantitative stress birefringence information are extracted respectively from the amplitude information and phase information. This method can achieve the complete stress information measurement and is especially suitable for the large-size samples.
Experiment study of wide range tunable femto-nano joule laser pulse output with flat top profile
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For the uniformity calibration of a detecting device, a tunable range output of femto-joule to nano-joule pulse with flat top profile beam is required. In this paper, a technique of producing the wide tunable range output of pulse energy with flat top profile is presented.
A highly sensitive fluorescence sensor for adrenaline detection based on modified carbon quantum dots
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Adrenaline (AD) plays a vital role in the functioning of the central nervous system and the cardiovascular systems. We proposed a fluorescence probe for adrenaline detection based on the modified carbon quantum dots (CQDs). Carbon quantum dots were synthesized by the hydrothermal method, in which citric acid was used as a carbon source, and then modified with ammonia solution. Fluorescence spectrophotometer, transmission electron microscope and Fourier infrared spectroscopy were used to characterize the modified CQDs, respectively. CQDs modified with ammonia have strong fluorescence intensity and emit blue light under ultraviolet light. The adrenaline was related to the quenching fluorescence of CQDs, which was caused by the electron transfer between CQDs and adrenaline quinone under alkaline conditions. The optimum pH value and reaction time of the adrenaline detection used by CQDs were determined to be 10.14 and 300 seconds, respectively. A good linear dependence between the fluorescence intensity ratio of the CQDs and adrenaline concentration(10~100uM) was found after the introduction of a modified Stern-Volmer equation.
Three-dimensional measurement system based on structured light and error correction
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This paper introduces one three-dimensional measurement system which based on structured light. This system has the advantages of high precision, high speed, and simple structure. In the three-dimensional measurement system based on structured light, the solution phase is one of the key steps. Phase jump, shadow and other errors will have a great impact on the final point cloud computing. This paper explains the three-dimensional measurement system, then also made an error analysis and proposed a corresponding solution. The reasons for the phase jump were analyzed and the corresponding solutions were proposed. This paper also analyzes the cause of random error and proposes a solution. The final accuracy was improved. This has important applications in contour extraction in workpiece repair and autopilot.
Deep fluorescent imaging with large field of view using automatic guide star selection
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The refractive index heterogeneity severely limits the imaging performance of optical microscopy in deep tissue. Adaptive optics (AO) is currently widely used to recover the diffraction-limited resolution at depth. However, there is a tradeoff between the time resolution and spatial resolution, which makes it difficult to achieve the real-time imaging in deep tissue. This is partially because that the effective correction area of conventional AO is limited with a single guide star (GS). Therefore, the using of multiple guide stars is a potential solution to increase the corrected field of view. Here we report an automatic selection algorithm of multiple guide stars and demonstrate the feasibility by implementing this method in the system of conjugate adaptive optical correction with multiple GSs. The simulation results indicate that compared with the case of the single guide star, high-resolution imaging can be obtained in most imaging areas with automatically selected 9 guide stars. Further, we can obtain optimally numbers and positions of the guide stars automatically and expect larger area aberrations. Therefore, this method has the great potential in in vivo deep tissue imaging.
Generating and tuning the Fano resonance by graphene oligomers with different nanostructures
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Fano resonance generating in graphene oligomers is systematically investigated in this study. The graphene oligomer is able to form plasmonic molecule due to the strong interaction between the graphene nanodisks, which is the basic of generation of Fano resonance. The optimization of Fano resonance is discussed by varying parameters of graphene oligomers such as the size of nanodisk, the chemical potential and the electron momentum relaxation time in midinfrared frequency. All these changes have a great effect on Fano resonance. Simultaneously, the environmental index sensing effect of the Fano resonance reaches a high sensitivity.
Surface distortion prediction method of KDP frequency converters
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KDP frequency converters are the important components applied in the final optics assembly for Inertial Confinement Fusion device. And the efficiency of second harmonic generation is much affected by phase matching error, which is induced by surface distortion. In this paper, focusing on the surface distortion under the specific mounting process of KDP frequency converters, we proposed an effective prediction method based on modified mechanical model to accurately predict the surface distortion during assembly. Using numerical simulation, we analyze the key elements that influence the surface distortion so as to adjust the mounting process according to the results. Results and findings in this article are meaningful for improving mounting-induced surface distortion of KDP frequency converters. Moreover, the mechanical model and prediction method presented will offer more efficient and reliable technical proposal for next generation ICF facility
Joint compensation of IQ imbalance and phase noise based on extended Kalman filter
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A joint compensation scheme for IQ imbalance and phase noise based on the extended Kalman filter is proposed. Our proposed scheme can compensate IQ imbalance and the phase noise jointly with quick convergence speed and excellent BER performance.
Optical frequency transfer over 377 km urban fiber link using EDFAs
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We demonstrate an optical frequency transfer over a 377 km-long fiber link using three bi-directional Erbium-doped fiber amplifiers (EDFAs) to compensate the fiber attenuation. Through active phase noise cancellation, we obtain a transfer instability of 2.2×10-14 at 1 s and 6.2×10-17 at 2000 s. The lasing effects induced by EDFAs are observed in the transfer link which reduce the gain performance of the EDFAs and deteriorate the stability of the signal. In the paper, the factors that may induce the lasing effects is discussed, specially, improper phase locking parameters may stimulate the lasing effects. The phase noise of the 377 km link and the transfer instability versus fiber lengths is also researched. This work makes a good foundation for our future research on long-distance optical frequency transfer.
Design of a foveated imaging system based on liquid crystal microlens array
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We propose a foveated imaging system (FIS) implementing by effectively correcting wavefront aberration, which mimics the human visual system to obtain a high resolution image for the regions of interest (ROI) while keeping a wide field of view (FOV). It is flexibly tuning the variation of the refractive index of liquid-crystal (LC) materials through adding variable AC voltage signals. A novel liquid-crystal microlens array (LCMLA) with three concentric ringelectrodes are presented, where three different AC voltage signals can be applied to corresponding ring-electrodes. There are three hexagon arrangement patterned electrode arrays with different diameters (equivalent to 98μm, 112μm and 140μm from the center to the periphery) in the concentric circles. The diameter of the MLA in the central field is the smallest, where the spatial resolution may be the highest. If appropriate AC voltage signals are added, the wavefront aberration of the incident light of ROI could be well adjusted. An experiment is developed to validate the performance of the FIS using LCMLA. The example images show that the proposed FIS can obtain local high resolution image of the ROI by dynamically controlling AC voltage signals and a total low resolution image over a wide FOV.
Inspection of polyethylene gas pipe defect based on terahertz time domain spectroscopy
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Polyethylene gas pipe sample with defects was detected by the transmission THz-TDS system. Firstly, the difference of the THz time-domain waveform and corresponding frequency spectra between the defect part and non-defect part was compared. Then, the PE pipe defects were imaged by the maximum value of THz time-domain data and the frequency-domain data. The results show that the existence of defects cause obvious reduction the maximum value of the THz time-domain spectrum. The PE defects can be clearly distinguished from the non-defect part by the transmission THz images. Imaged by the THz timed-domain and the frequency-domain parameter can reveal the defects in the polyethylene gas pipe.
Feature extraction of Brillouin scattering spectrum based on half-interval search frequency sweep method
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In order to improve the real-time performance of Brillouin optical time-domain analysis (BOTDA) distributed optical fiber sensing system, this paper proposes an extraction method of Brillouin scattering spectrum based on half-interval search frequency sweep. This method shortens measurement time by reducing the frequency sweep range, and provides a simplified Brillouin gain spectrum. Cross-correlation of this spectrum with a standard Lorentz curve, then the ideal Lorentz line type near the peak of the convolution result is used for frequency shift feature extraction. And the estimated value of Brillouin frequency shift (BFS) can be calculated by the result of frequency shift feature extraction. A 15km Rayleigh BOTDA temperature sensing experiment is designed to verify the reliability of the method. The results show that this method avoids extension of measuring time caused by the complex iterative process, and reduces frequency sweep time. It has better real-time performance and measurement accuracy than traditional Lorenz curve fitting (LCF) which based on the Levenberg-Marquardt (LM) algorithm.
Efficient light trapping in ultrathin-crystalline-silicon solar cells using TiO2 nanosphere arrays
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Ultrathin-crystalline-silicon solar cell is important for its low cost and flexibility, but its efficiency is low. Light trapping technology is a useful way to improve the efficiency. In this paper, we design a TiO2 nanosphere arrays on the top of the ultrathin-crystalline-silicon solar cells with 2-μm-thickness to achieve advanced light trapping property. The finite element method is used to study the optical properties of the sphere nanostructure on the ultrathin-crystalline-silicon solar cells. The light trapping ability is systematically studied by COMSOL multiphysics. The results show that the sphere nanostructure can highly increase the light absorption of the ultrathin-crystalline-silicon in the wavelengths from 300 to 1200 nm. The average absorption rate increases by 58.63% compared to 2-μm-thick crystalline silicon.
Application of BRDF data in stray light analysis
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For the Tiangong-1/Shenzhou-spaceship rendezvous and docking mission, the problems in the work of rendezvous and docking sensors in various complicated environments were analyzed. To improve the measurement accuracy of sensors, measurement and research work on the BRDF (Bidirectional Reflectance Distribution Function) of spacecraft cladding materials was conducted in terms of stray light analysis in optical systems. In order to verify the applicability of the BRDF data, the rendezvous and docking sensor was chosen as the analysis object, to compare the changes of the imaging quality of the optical system before and after using the BRDF data.
Generation of Hermite-Laguerre-Gaussian beams based on space-variant Pancharatnam Berry phase
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This paper presents a novel method for generating Hermite-Laguerre-Gaussian beams based on a spiral phase plate and a metasurface. The spiral phase plate is used to generate and modulate the dynamic phase, which has been used to generate the Laguerre Gaussian beam. The metasurface of the spatial variation can modulate the geometric phase for generating the Hermite Gaussian beam. We found Pancharatnam-Berry phase changed over the propagation of Hermite-Laguerre-Gaussian beams in free space, and the beam rotated around the phase singularities, the chirality of circular polarization of the incident beam will change. The theoretical analysis results are verified by a simple experimental system. The Pancharatnam-Berry phase provides a new degree of freedom. The study provides the theoretical and experimental basis for manipulating of the vortex light field based on the metasurface.
Analysis and application of vortex optical characteristics based on Michelson interference
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The vortex light containing orbital angular momentum (OAM) has important application prospects in precision measurement, micro particle manipulation and basic physics. Because the Poynting vector of the vortex wave is not in line with the direction of the optical axis, more information is contained in the echo than the ordinary electromagnetic wave, so it has a unique advantage in the detection of unknown object. The wave propagation characteristics of the vortex beam are modeled and analyzed. Based on the Michelson interference principle, a new type of vortex light interference scheme is designed. The measurement scheme of the wavelength of the vortex light is proposed and the experimental verification is carried out. On this basis, a new method for detecting non-cooperative targets in space is proposed and analyzed theoretically. It provides a new way for measuring angular velocity of objects by vortex optics, and lays a good foundation for remote sensing of non-cooperative targets in actual demand in the future.
Pilot aided OSNR monitoring in optical Nyquist transmission system
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A method of using pilot-tone to monitor optical signal-to-noise ratio (OSNR) is proposed in the paper. High-order statistical moments of pilot component are utilized to evaluate the noise level of the transmitted optical signals. This method of OSNR monitoring has the advantage of insensitivity to chromatic dispersion (CD) and polarization mode dispersion (PMD). Simulations are carried out in optical Nyquist transmission system. It is shown that the method has 1 dB monitoring accuracy over a wide OSNR range from 5 dB to 25 dB.
A 2.2J all-diode-pumped Nd:YAG burst-mode laser at repetition rate of 10kHz
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An all-diode-pumped Nd:YAG burst-mode laser was demonstrated. A diode-laser-side-pumped Nd:YAG laser with Qswitcher, as laser oscillator, was employed to produce burst pulse directly. When the diode-laser worked at 10Hz and Qswitcher was operated at 10kHz, a maximum burst energy of 456mJ was obtained in the master oscillator with the highest optical efficiency of ~30%. Each burst included 19 pulses in the pumping duration of 2ms. A master oscillator and power amplifier architecture was adapted to scale the burst energy to meet PLIF system applications. The burst energy of 456mJ obtained from laser oscillator was amplified to 2.2J by use of three diode-laser-side-pumped Nd:YAG modules as laser amplifiers. The energy extraction efficiency of each stage was achieved to ~13%, ~22% and ~24%, respectively. The single pulse energy of 1064nm laser at 10 kHz reached to ~116 mJ with pulse width of 9.8 ns and a peak power of ~11.8 MW. The performances of pulse-burst laser we constructed can be better and improved greatly by use of more amplifiers.
Tunable ultra-broadband microwave frequency combs generation using semiconductor laser injected by intensity-modulated light
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This paper proposes and demonstrates a generation scheme of tunable ultra-broadband microwave frequency combs (MFCs) based on a semiconductor laser injected by intensity-modulated (IM) light. The IM light is obtained by current modulating the master semiconductor laser. Then the IM light is injected into the slave semiconductor laser. The influences of the injection strength, frequency detuning, modulation index and modulation frequency on the MFCs generated were investigated by numerically simulating the rate equations of a semiconductor laser with optical injection of IM light. The simulation results show that under appropriate injection parameters, in an amplitude variation range of ±5dB, the bandwidth of the microwave frequency combs can reach over 60GHz, even 108GHz. The comb space of the MFCs can be tuned by the frequency of the modulation signal. Compared with the scheme of optical injection and current modulation into a slave laser, the proposed scheme has an advantage of 28GHz in peak bandwidth of the MFCs generated under the same conditions. In conclusion, the proposed scheme is a simple and effective generation method of tunable ultra-broadband microwave frequency combs.
Enhancing the performance of BOTDA sensing through introducing additional pre-exhausted wavelength
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This paper presents and experimentally demonstrates a novel scheme of Brillouin optical time domain analysis (BOTDA) sensing system to ensure the encoded pulse waveform amplified from EDFA is flat. This system also can eliminate the noise by introducing additional pre-exhausted wavelength at the laser. The experiment results indicate that this dual-wavelength pump light scheme can easily shape the Lorenz curve between Brillouin gain spectrum(BGS) and scan frequencies without any extra processing, compared to normal BOTDA system with single-wavelength pump light. The new scheme can also improve the intensity of Brillouin signal about 50mV as well as the frequency shift accuracy is increased by 5MHz, which is benefit for increasing sensing range and measurement accuracy.
Incoherent digital holography using geometric phase
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A self-interference digital holographic system based on geometric phase modulation is presented. The holographic recording under the natural light or general illumination sources is possible with simple and compact form factor.
Effective improvement of subtraction method for light sheet fluorescence microscopy via tangent-function subtraction coefficient
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Light sheet fluorescence microscopy (LSFM) with fluorescence emission difference (FED) obtains axial resolution-enhanced images by the subtraction of signals excited by different light sheets, Gaussian light sheet and negative light sheet. Negative values are inevitable in FED LSFM with conventional subtraction coefficient, due to mismatches in the outer contours of the raw signals excited by different light sheets, causing image distortion. In this paper, we propose a method based on tangent-function subtraction coefficient to reduce image distortion. This tangent-function subtraction coefficient is introduced to minimize image distortion without lowering the axial resolution. The value of the variable subtraction coefficient is obtained from the intensity value of raw signals. We performed experiments using fluorescent beads with a diameter of 1 micron and compared the subtraction results with constant and tangent-function subtraction coefficient. The experimental results demonstrated that the proposed tangent-function subtraction coefficient has an advantage over the conventional constant coefficient.
Photonic bandgap properties of integral photonic crystals and photonic crystals with defects in polymer
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We report various photonic crystals (PhCs) structures by using the femtosecond laser-induced two-photon photopolymerization of SU-8 resin. The bandgap properties were investigated by varying the crystal orientations in <111>, <110> and <100> of diamond-lattice PhCs. The photonic stop gaps were present at λ=3.88 μm in <111> direction, λ=4.01 μm in <110> direction and λ=5.30 μm in <100> direction respectively. In addition, defects were introduced in graphite-lattice PhCs and the strong localization of photons in our structure with defects at λ=5 μm was achieved. All the above work shows the powerful capability of femtosecond laser fabrication in manufacturing various complicated three-dimensional photonic crystals and of controlling photons by inducing defects to the PhCs samples.
Microwave frequency divider with variable dividing ratio based on a tunable optoelectronic oscillator
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A 24 GHz microwave frequency divider with variable frequency dividing ratio based on a super-harmonic injectionlocked tunable optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. Due to the nonlinearity of the dual-output Mach-Zehnder intensity modulator (DOMZM) and the photodiode (PD) used in the OEO loop, it can generate intermodulation components between the 24 GHz injection RF signal and the harmonics of the free-running OEO. If the frequency of any one of the intermodulation components locates at the locking range of the free-running OEO, the phase of the OEO will be synchronized to the 24 GHz injection RF signal. It realizes a microwave frequency divider. By tuning the oscillation frequency of the OEO to the second, third, or fourth sub-harmonic of the 24 GHz input RF signal, a microwave frequency divider with variable frequency dividing ratio of 2, 3, or 4 is realized. The achievable frequency dividing ratio is limited by the nonlinearity of the DOMZM and the injection RF power. A good phase noise performance of the OEO lead to a microwave frequency divider with low phase noise. The transient response of the RF phase of the output of the OEO during the process of super-harmonic injection locking is also measured.
20 GHz optical pulse generation based on a 10 GHz optoelectronic oscillator
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An optical pulse generation with repetition-rate of 20 GHz based on a 10 GHz optoelectronic oscillator (OEO) is proposed and experimentally demonstrated. The combination of an optical comb generator (OFCG) and an OEO can generate an optical pulse train with the features of high repetition-rate, narrow pulse-width and low timing-jitter, simultaneously. By tuning the DC bias voltage applied on the OFCG, the modulated output light of the OFCG appears as a 20 GHz single optical pulse train which has a repetition-rate twice of the 10 GHz modulation frequency of the OFCG. It improves the repetition-rate of the optical pulse. A microwave frequency divider with dividing ratio of 2 is used to obtain an electrical signal with frequency equals to the 10 GHz modulation frequency. The output of the microwave frequency divider is fed back to drive the OFCG to form a closed OEO loop. Compared with the former ways, it eliminates the optical bandpass filter (OBPF), which improves the power efficiency of the OEO loop.
Role of nanocone and nanohemisphere arrays in improving light trapping of thin-film solar cells
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The optical trap of thin-film silicon solar cells is very important for improving efficiency and reducing cost. A composite nanostructure with front silicon nanocone gratings and rear Ag nanohemisphere gratings is proposed. The relationship between the geometrical parameters of the hybrid nanostructures and the optical properties of the silicon solar cells was studied using the finite element method. The light-harvesting ability was studied systematically using COMSOL Multiphysics. The simulation results show that the optimum parameters of the front silicon nanocone grating are a diameter of 350 nm, height of 250 nm, and pitch/diameter ratio of 1.1. The optimum parameters of the rear Ag hemispherical grating are a diameter of 270 nm and pitch/diameter ratio of 1.4. The average absorption of the hybrid nanostructure solar cell is 78.5%, and the short-circuit current density is 36.6 mA/cm2, representing an enhancement of 171.1% compared with that (13.5 mA/cm2) of the reference cell.
Graphene enhanced phase sensitive D-type fiber optic sensor
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A new D-type fiber optic sensor based on silicon/graphene hybrid structure is proposed. The refractive index variations are detected with phase difference changes instead of the conventional intensity and spectral variations. An ultrahigh phase sensitivity of 1:3716×106 deg=RIU (RIU: refractive index unit) was achieved, which is 3447- fold and 380-fold higher than that of fiber optic sensor without silicon/graphene coating, and with only silicon coating, respectively. This phase sensitivity enhancement factor is depending on the incident angle. The phase sensitivity decreases with the incident angle, height of fiber core, while increases with the length of sensing region.
X-ray phase-contrast imaging using cascade Talbot-Lau interferometers
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Grating-based X-ray phase-contrast imaging (XPCI), have shown great potential for biological and medical imaging applications. However, the fabrication of the absorption grating, an indispensable element in conventional Talbot-Lau interferometer (TLI), making it a great challenge to this technology into practical use. In this paper, we implemented a cascade TLI (CTLI) for XPCI composed by a TLI and an inverse TLI, the self-image of TLI being used as the source of the inverse TLI, with the purpose to avoid the fabrication of small-period high aspect-ratio absorption gratings. Experiments validated the method and demonstrated the versatility and tunability of the system. The angular sensitivity as a function of the sample position was measured and discussed. Results show that the highest sensitivity is obtained, when the investigated object is close to any of two phase gratings. Furthermore, a CTLI with interference fringes being magnified to be directly detected by a common large-area detector would be established using this method. This will be useful for designing an XPCI system for applications of biomedical imaging in large field of view.
Experimental study of magneto-acousto-electrical tomography based on laser-generated ultrasound technology
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In this work, a magneto-acousto-electrial tomography (MAET) method based on laser-generated ultrasound excitation was proposed for high-spatial-resolution images of the impedance of conductive media. Optically generated ultrasound is reported with broad bandwidth and insensitive to electromagnetic interference (EMI). Composite films were used as the optoacoustic sources, which composed of candle soot (CS) and elastomeric polymers. To characterize the laser-generated ultrasonic waves, laser Doppler vibrometer was adopted as the detecting device making the system totally optical while maintaining millimeter-level resolution and detective depths of several centimeter. Photoacoustic waves were then introduced to a sample of different conductivity distribution by laser-generated ultrasound transmitter at one point and detected by a pair of electrodes on the surface of the sample. Due to the absence of EMI between acoustic excitation and magnetic field, the combination of non-electronic ultrasound generator and low-cost, non-invasive MAET have shown its great capacity for effective early tumor assessment.
Frequency-resolved photoacoustic viscosity measurement
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In this paper, we proposed a photoacoustic (PA) method for detecting liquid viscosity based on frequency-resolved measurement. A negative correlation was investigated theoretically between the liquid viscosity and the full width at half maximum (FWHM) of the PA frequency spectrum. To test the feasibility of this method, water mixed with different concentrations of ink and glycerol was measured. The results indicate that liquids with higher viscosity will lead to a higher FWHM reduction in the PA frequency spectrum and the frequency spectrum was independent from the absorption coefficient of the liquid, which demonstrate that this technique has future potential clinical applications for monitoring the viscosity changes in subcutaneous microvasculature.
Low-energy IR780 nanoemulsion for photodynamic therapy
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As a near-infrared photosensitizer, IR780 is a promising agent for photodynamic therapy. However, its clinical application was limited by its poor aqueous solubility and chemical stability. Therefore, the purpose of this study was to prepare IR780 encapsulated nanoemulsion (IR780-NE) to enhance the solubility and chemical stability of IR780, using a low-energy emulsion inversion point (EIP) method, which could avoid complex procedure and IR780 degradation during preparation process. The IR780-NE presented a homogeneous and clear appearance, as well as a mean droplet diameter of 38.17 ± 3.59 nm, as determined by dynamic light scattering. The IR780-NE greatly enhanced the chemical stability of IR780, with more than 80% IR780 retained after storage at 25 °C for 4 days. The IR780-NE also showed satisfactory physical stability, with no alteration of mean droplet diameter during storage at 25 °C for 4 days or 4 °C for 30 days. The zeta potential of the IR780-NE was nearly zero (-0.27 ± 2.06 mV), and the ultraviolet-visible light absorption spectrum showed that the near-infrared light absorbing ability of IR780 was not influenced. In conclusion, the IR780-NE is a potential delivery system for the application of IR780 in biological systems.
Application of hyperspectral imaging technology in nondestructive testing of fruit quality
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Hyperspectral imaging (HSI) technology is a multidimensional information acquisition technology that combines imaging and spectroscopic techniques. It can not only visually display the external quality characteristics of the objects to be measured, but also reflect the differences in their internal chemical composition. HSI is playing an increasingly important role in rapid and non-destructive testing of fruit quality. In this paper, we discuss the application of HSI in the identification of small tomato varieties and the detection of pesticide residues. The back propagation neural network (BPNN) and support vector machine (SVM) algorithms were used to establish the variety identification and pesticide residues concentration analysis models. By using multiplicative scatter correction (MSC) pretreatment the accuracy of the two models reached up to 100%. The current study indicates that combining HSI technology with proper algorithm can provide an efficient method to identify small tomato varieties and detect pesticide residues.
Enhanced performance of high-speed IM/DD DMT systems using an EM channel estimation algorithm for short reach optical communication
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A semi-blind Expectation-Maximization (EM) channel estimation algorithm is proposed for 50 Gb/s quadrature phase shift keying (QPSK)-Discrete MultiTone (DMT) signal transmission systems using intensity modulation/direct detection (IM/DD) over 100 km standard single mode fiber (SSMF). The reported channel estimation methods for DMT systems can be roughly divided into two categories: semi-blind channel estimation and blind channel estimation. Due to the low accuracy of traditional blind channel estimation algorithm and lower spectral efficiency of the semi-blind channel estimation algorithm relying on more training sequences (TS), EM algorithm is proposed that is a two-step iterative procedure to maximize the likelihood function for achieving channel estimation instead of classical semi-blind channel estimation methods with more TS. Also, we assume the channel of the IM/DD DMT system as an additive white gaussian noise (AWGN) channel. Simulation results show that using EM algorithm yields about 2 dB optical signal noise ratio (OSNR) improvement at a bit error ratio (BER) of 3.8×10-3 compared to classical channel estimation based on TS under the same number of TS and has the similar performance compared to classical channel estimation relying on more TS. In addition, it is shown that at high OSNR (>19 dB), the performance of EM algorithm outperforms that of LMS algorithm. On the contrary, the performance of least mean square (LMS) algorithm outperforms that of EM algorithm at low OSNR (<19 dB).
Cell imaging with squaraine dye based on two-photon excitation fluorescence imaging
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Two-photon excitation fluorescence imaging (TPEFI) is widely used in biomedicine because it has advantages of low cytotoxicity, high resolution and deep imaging depth. In this experiment, OVCAR-3 ovarian cancer cells were labelled with the squaraine dye and detected by confocal laser scanning microscope ( Leica TCS SP8 )for single-photon and two-photon imaging. The results showed that the squaraine dye can be used well to two-photon imaging.
Non-reciprocity induced by the nonlinear optical effect in microring structure and its application in optical sensing
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A structure in photonic integrated circuit with a microring serially connected by an optical attenuator is proposed to generate the non-reciprocity by the nonlinear optical effect in microring. We find that when the information of the transmission spectra of both forward and backward directions is utilized for sensing, the precision of sensing can be enhanced. We calculate the non-reciprocity ratio of our proposed structure, and utilize this spectrum for sensing. Simulation shows the non-reciprocal spectrum varies with the attenuation value of the attenuator. The slope of 4.34dB/GHz can be achieved by utilizing 10dB attenuator, and the sensing frequency range is 7.35GHz. These results benefit its application in sensing.
Study of the internal hollow structures fabricated with two typical femtosecond laser systems and their respective applications
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Femtosecond (fs) laser is proved a powerful tool in the field of 3-dimensional internal micromachining inside the transparent dielectrics. There are already many types of femtosecond laser systems widely applied nowadays, among which Ti: sapphire femtosecond laser and femtosecond fiber laser are the two most frequently used typical femtosecond laser systems. However, according to our study, the differences in the laser parameters between these two femtosecond laser systems may induce significant discrepancy in manufacturing internal hollow structures inside the polymethyl methacrylate (PMMA) substrate. The experimental results show that when a 65fs laser beam is focused inside the PMMA substrate and scans a route of a straight line at an average power of 1.5W and 1 kHz repetition rate, a hollow microchannel is successfully fabricated and no melted region is found around the microchannel. However, if the PMMA substrate is constantly irradiated with the 1.5W laser pulses that generated by a 400fs femtosecond fiber laser system at a repetition rate of 100 kHz, a growing hollow cavity is observed and a melted-resolidified region is formed around the cavity. According to the numerical simulation of heat accumulation effect, we explain the ‘heat accumulation effect’ caused in the femtosecond fiber laser manufacturing and the ‘cold processing property’ of the Ti: sapphire femtosecond laser processing, respectively. These experimental and numerical results may broaden the understanding of thermal effect during the process of the femtosecond laser micromachining and provides more opportunities in the manufacturing of polymeric integrated microfluidic chip with laser direct writing technology in the future.
Hyperspectral imaging of rare-earth doped nanoparticles emitting in near- and short-wave infrared regions
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Comparing to other optical imaging techniques, hyperspectral imaging (HSI) possesses a unique feature, being capable of not only obtaining a spatial information about a specimen, but also providing a spectral information in every image pixel. Being employed in biomedical applications, similarly to other optical bioimaging techniques, HSI struggles with limited light penetration depth, caused by high absorption and scattering of light by biological tissues. Overcoming the limitations of imaging in visible spectral range, optical bioimaging in near-infrared (NIR) and short wave infrared (SWIR) spectral ranges (~700 –1700 nm) has being actively advanced in recent years, as due to the strongly reduced tissue absorption and scattering, NIR-SWIR imaging systems can achieve deeper tissue imaging with higher resolution. With the aim to combine both the advantages of SWIR imaging and HSI, we have built a hyperspectral imaging system operating in NIR-SWIR spectral region (900 – 1700 nm). The constructed HSI system is based on a wavelengths scanning method, with a liquid crystal tunable filter (LCTF) as a dispersion element. The spectral unmixing software has been developed to map the regions of the specified spectral features. Finally, an application of the developed method towards spatial differentiation of rare-earth doped nanoparticles emitting in NIR-SWIR range has been demonstrated.
Synthesis and luminescent properties of rare earth doped upconversion nano-fluorapatite
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Bone defect is a common clinical disease, regeneration and repair of the damaged hard tissue is still a huge challenge in the biomedical field. In recent years, rare earth ion doped apatite upconversion luminescent nanomaterials have wide application prospects in tracing the situation of repair the damaged hard tissue and bioimaging due to their unique physical and chemical properties. The focus of this study is to further improve the luminous property of apatite upconversion nano materials for biomedicine. Rare earth ions Yb3+/Ho3+ doped nano-fluorapatite (FA: Yb3+/Ho3+) were prepared successfully by hydrothermal method. Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier Transform Infrared Spectrometer (FTIR), fluorescence spectroscopy were used to characterization the morphology, crystal structure, chemical composition, and luminescence properties of Yb3+/Ho3+ doped nano-fluorapatite. The results showed that Yb3+/Ho3+ doped nano-hydroxyapatite material rod-shaped and has a hexagonal crystal structure. By adjusting the doped proportion of the rare earth Yb3+ and Ho3+ ions, upconversion luminescence efficiency of the material has greatly improved. The strongest emitting of FA: Yb3+/Ho3+ nanomaterials is when the doped proportion of the rare earth Yb3+ ions reach to 60% and Ho3+ ions reach to 3%. Thus, this kind of FA: Yb3+/Ho3+ nanomaterials have good upconversion luminescence properties can provide favorable conditions in cell markers and imaging. It is expected to promote their wider application in the biomedical field.
Photonics-based dual-band RF receiver with large crosstalk suppression
Jiang Liu,
Dan Zhu,
Wenjuan Chen,
et al.
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A dual-band RF receiver with large crosstalk suppression is proposed and demonstrated based on photonic imagereject mixing and polarization multiplexing. Dual-band RF signals in the X- and Ku-bands with 1-GHz instantaneous bandwidth are simultaneously downconverted to the same IF band with crosstalk suppression of large than 30 dB.
Overlapped fingerprint image capture and separation using digital holography and machine learning
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Even now that DNA test has become common, latent fingerprints are still a useful evidence for finding criminals. However, the latent fingerprints are often damaged and overlapped with each other. At present, these overlapped fingerprints are separated manually by a person. It is not only time-consuming task, but also less likely to be adopted as evidence because it is difficult to rule out of the intention of a person. In this paper, non-destructive method to capture and separate overlapped fingerprints using digital holography and machine learning is presented and demonstrated.
A biologically inspired solution for allocation problems of branch-cuts
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Branch-cut is a classical algorithm in phase unwrapping algorithm based on path-following approach. Goldstein’s branch-cuts algorithm is prone to generate large enclosed areas and produce longer branch-cuts. Models inspired by biosystems can provide new insights into complex computing problems in the real-world. A unicellular and multi-headed slime mold, named as Physarum polycephalum, has been a research hotspot over the last few years. According to the two characteristics of Physarum: the adaptive shortest path finding and adaptive network formation, researchers combined the Hagen-Poiseuille and Kirchhoff law to establish bionic mathematical model: the maze-solving model to get shortest path between two points and multiply sources model for designing efficient network. In this paper, based on these bionic models, combined with the foraging characteristics of Physarum, a biologically inspired algorithm called Physarum Foraging Algorithm (PFA) is proposed for allocation problems of branch-cuts. Firstly, according to the distribution characteristics of residues in the interference fringes map, the residues were processed; secondly, using the bionic model to build a branch-cuts network between residues; finally, the Physarum exhibits a characteristic that the critical tubes are reserved in the process of foraging, using this unique feature to optimize the branch-cuts network, then complete reconstruction of branch-cuts. PFA cannot only significantly cut down the overall length of branch-cuts but also effectively overcome the ‘isolated island phenomenon’ in the unwrapping process. Experimental result showed that the algorithm implements optimal allocation problems of branch-cuts which greatly improves the accuracy of phase unwrapping.
See-through near-eye display using lightguide and transmissive type optical eyepiece: index-matched anisotropic crystal lens
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Various optical eyepieces have been recently proposed for augmented reality head-mounted display. Most of optical eyepieces are based on the reflective optical element including half convex mirror, free form optics and diffractive optical element. We present the transmissive type optical eyepiece: index-matched anisotropic crystal. Also, to compensate the long focal length which is an inherent drawback of index-matched anisotropic crystal, a lightguide is applied to the system. The experimental results and field-of-view analysis are presented to show the feasibility of the proposed idea.
Opto-acousto-fluidic microscopy for three-dimensional imaging of droplets and cells
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This paper reports a novel method, opto-acousto-fluidic microscopy, for label free detection of droplets and cells in microfluidic networks. Leveraging the optoacoustic effect, the microscopic system possesses capabilities of visualizing flowing droplets, analyzing droplet contents, and detecting cell populations encapsulated in droplets via the sensing of acoustic waves induced by intrinsic light-absorbance of matters. The opto-acousto-fluidic chip was fabricated using standard soft-lithography with a channel width of 200 μm and height of 120 μm. Fluid samples were injected into chips using syringe pumps via plastic tubings. A T-junction was used to produce aqueous droplets which consisted of light-absorbing molecule species or cells and buffer fluids. A pulse laser beam (repetition rate 50 kHz) steered by a galvanometer mirror and focused by an objective (4X) transmits through and converges with a focal spot size of 3.2μm in the microfluidic channels. For each scanning line, 250 sampling was made with a spatial interval of 1 μm across the channel with a width of 200 μm in the experiment, and thus the 50kHz repetition rate of the laser provides a 200Hz B-scan rate. In the cell research, arterial blood was draw from a rat and buffered with saline. Droplets with different volumes but same density of red blood cell population were generated, and the cytometric measurement shows that the number of detected RBCs increases proportionally with the volume of the droplet.
Enhancement of plasma resonance in a Hi-Bi D-shaped photonic crystal fiber SPR sensor
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A D-shaped fiber surface plasmon resonance (SPR) sensor based on a Hi-Bi photonic crystal fiber (PCF) is investigated with finite element method. Through changing the size of the air holes beside the fiber core, it is found that the Hi-Bi structure can enhance the plasmon resonance at mid-infrared wavelength. The effect of the two fiber core side holes as well as the different gold film thickness on plasmon resonance is numerically investigated. A high and sharp loss peak is achieved, which indicates that the sensor should have high accuracy. The sensitivity of this D-shaped PCF sensor is obtained to be 8920nm/RIU in the range of 1.37 to 1.39 and the power sensitivity is 154 dB/(cm·RIU) in the range of 1.33 to 1.36. Particularly, near 1.36, with the detection limit of 0.1 nm the resolving power of the sensor is lower than 10-4 RIU with a figure of merit of 28.6.
Experimental study on laser power influence for diamond grits brazing
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High power transverse flow CO2 laser was used to scan the brazing alloy and diamond grits, the paper studied the influence of laser power on brazing layer combination performance and diamond grits thermal damage, analyzed the thermal damage mechanism of laser brazed diamond and combination mechanism of brazing layer and diamond grits. The research result showed that laser power is one of factors for diamond thermal damage, under high laser energy input, oxidation took place between diamond grits and oxygen outside, diamond would be oxidized all along on the condition of branch gas pressure about free equation until the balance established between diamond and oxide, during this process, diamond grits would be carbonized or burn out and gasify.
The study of the intracellular transportation of gold nanoparticles through dark field imaging
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In this work, gold nanoparticles coated with CTAB were used as probes for studying the interactions between nanoparticles and cells. The dark field scattering spectra from cells were obtained at different time points after they were treated with gold nanoparticles. By analyzing the results, we find that the dark field scattering spectrum changes at different time points, which is of certain significance in studying the interactions between cells and gold nanoparticles.