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- Front Matter: Volume 11068
- Novel Technology of X-Ray Imaging
Front Matter: Volume 11068
Front Matter: Volume 11068
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This PDF file contains the front matter associated with SPIE Proceedings Volume 11068, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.
Novel Technology of X-Ray Imaging
Study on multiphase diffusion reaction for interface of magnesium particle in microscale
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Combustion mechanism of magnesium has long been explored. It has been recently shown that spherical magnesium particles with highly active can be used to analyze combustion process in detail with the help of new methods and advanced instruments. This work is aimed at investigating the multiple diffusion reaction of single spherical magnesium particles in accordance with surface composition and combustion remains. Energy Dispersive Spectrometer (EDS), Scanning Electron Microscope (SEM) and X-ray Diffraction (XRD) were used to analyze the samples before and after reaction. In addition, combustion of magnesium particle was conducted in a microscope heating system. The results of the study show that an oxygen-rich layer formed on the particle surface before the particle was heated to burn. Dissolved oxygen was detected in this layer and its concentration is lower than that of stoichiometric MgO. The dissolution reaction of oxygen begins before the gas phase combustion and later on, after the gas phase combustion stops, becomes the dominated reaction. It is suggested that there are two sources of MgO formed during the oxidation process, Mg(s) → Mg(g) → MgO(s) and Mg(s) → oxygen-rich layer(s) → MgO(s). The latter is the dominated mechanism of surface heterogeneous reaction.
Research on strain field monitoring system of irregular surface workpiece
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In order to ensure the assembly precision in the digital assembly process of large workpiece and reduce the assembly error caused by the standard point coordinate offset caused by surface deformation, an irregular surface workpiece strain field monitoring system based on FBG sensing array was designed. The system tests the surface deformation of the workpiece with gradient features by means of an FBG array laid on the surface of the workpiece. It can calculate the micro-displacement offset of the standard point of the workpiece. The simulation results show that the strain is related to the position, size and workpiece structure of the force application. The strain field has a significant gradient change on the surface of the workpiece. In the experiment, the FBG array arrangement was completed according to the strain gradient feature distribution. Each FBG can effectively acquire the dependent variable at each point. The relationship between the amount of micro-displacement and the wavelength shift under different applied conditions is obtained. The error distribution of the micro-displacement amount is calculated. It verifies the feasibility of the system.
Application of intra-symbol frequency domain averaging algorithm in IM/DD 16QAM OFDM
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We apply the intra-symbol frequency domain averaging (ISFA) channel estimation algorithm to the intensity modulation and direct detection (IM/DD) 16QAM orthogonal frequency division multiplexing (OFDM) system and improve the performance of the system. In the paper, the weighting coefficients in the algorithm are changed to obtain the best system performance. In order to study the applicability of the algorithm, the number of different subcarriers is simulated and better system performance is obtained. In the case of changing the transmission distance, we compare the performance of traditional algorithms and ISFA.
Finite-element-method study of the thermal distortions of deformable mirrors for laser systems
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In order to analyze thermal distortions of the deformed mirror for laser systems, the finite element model of a 417-element deformable mirror was built. The deformation, temperature rising and high-order aberrations were calculated after applying the laser irradiation to the mirror. Based on the results, we found the distortions became larger and larger while the absorption of multilayers increasing. When the mirror thickness is 1 mm, the deformation and temperature rising were 0.370 μm and 6.68 ℃ respectively. The PV decreased from 0.370 μm to 0.256 μm when the mirror got thicker from 1 mm to 3 mm, and the corresponding removed low-order Zernike coefficient residual error was reduced from 0.285 μm to 0.145 μm. The high-order aberrations of the deformed mirror were little when the mirror surface thickness was 3 mm. The results have practical engineering application for the design of deformable mirrors for laser systems.
Study on characteristics of laser acoustic vaporization mechanism
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Laser acoustic is a new way to generate underwater sound sources. Photoacoustic signals have the advantages of high sound intensity, narrow pulse, wide spectrum and long-range excitation. In this paper, the related characteristics of vaporization mechanism of laser induced acoustic are studied. The characteristics of vaporized acoustic signal and photoacoustic conversion efficiency are theoretically analyzed. The principle experiment of laser induced acoustic is designed. The waveform and spectrum of acoustic signal are analyzed. The result of research can provide a reference for the optimization of laser acoustic conversion efficiency.
Experiment study on laser amplification with twins fiber
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A novel kind of domestic twins fiber that consisted of active unit and passive unit was researched in this paper. The slop efficiency of the twins fiber was observed via various laser amplification testing systems, which were respectively established with two different pump wavelengths and two different numerical apertures of pump output fiber. The effect of both pump wavelength and numerical aperture on the slop efficiency of the twins fiber was analyzed during the experiment. After the laser amplification testing system was optimized, the slop efficiency of the twin fiber increased from 72.1% to 82.1%. The numerical aperture of the pump output fiber would exert a distinct influence on the slop efficiency of the twins fiber. Simultaneously, the method to improve the slop efficiency of the twins fiber and decrease heat generating in high power fiber laser system was suggested.
First principles study on electronic structure and optical properties of SrI2 and SrI2: Eu
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Based on the first principle of density functional theory, we study the band structure, electron density and optical properties of SrI2 and SrI2: Eu crystals. The exchange and correlation potential is calculated using the first principle of generalized gradient approximation (GGA). Our research results show that the crystal volume of SrI2 after doping has decreased; SrI2 and SrI2: Eu crystals have band gaps of 3.909eV and 0.398eV, respectively, indicating that the electrons after doping transition from the valence band to the conduction band require less energy. Judging from the distribution of state density, the peak width of the valence band near the Fermi level increases, and the Eu doping adds a small peak to the valence band near the Fermi level. These phenomena show that doping can produce more visible scintillating photons when exposed to the same radiation. SrI2 and SrI2: Eu: the blue shift occurred on the absorption edge, the mixing reduced the absorption of low energy photons in the crystal as a whole. At the same time, in the high-energy area, the absorption coefficient rises from 110000cm-1 to 130000cm-1 , and doping with Eu increases the detection efficiency of the scintillation. This study can explain the increased detection efficiency of doped scintillation. The research in this paper provides the theoretical basis for the study of the mechanism of SrI2 emission, and also provides the theoretical reference for the research of SrI2 doping
UAV laser charging technology based on beacon laser alignment
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Laser is used for remote charging of UAV instead of sunlight to improve charging power, continuous charging performance and endurance of UAV. Laser alignment is one of the key technologies for laser charging. On the basis of briefly describing the composition and working process of the laser charging system, the method, module composition, working process and key process based on beacon laser alignment are emphatically analyzed. Combined with the whole working process of the laser charging system, the error factors affecting the charging accuracy are analyzed, and the reasonable error distribution is carried out to provide theoretical basis for the system realization.
Design and implementation of the infrared dynamic camouflage array
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In order to improve the target's antagonism to the infrared reconnaissance and recognition, an infrared dynamic camouflage array based on the electro-thermal material is designed. The overall design scheme and the structure of the regional temperature control drive module are described. The main dynamic factors of external environment and internal controllable factors of temperature control are analyzed. Through processing, assembly and debugging, the camouflage array prototype is completed, and the controllable dynamic camouflage effect is achieved. Then the temperature control accuracy and radiation uniformity are tested, and the error is analyzed.
Low-BER communications in optical networks-on-chip using coding technology
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The traditional optical networks-on-chip (ONoCs) communication systems is susceptible to crosstalk noise, especially the Wavelength Division Multiplexing (WDM) based ONoCs with nonlinear noise caused by four-wave mixing (FWM) effects. Crosstalk noise greatly reduces the performance and improves the bit error rate (BER) of the ONoCs. In this paper, a low BER communication system in ONoCs based on linear block codes is proposed. Firstly, we designed a all-optical linear block codes generator based on microring resonators(MRRs) to encode the information transmitted in the ONoCs before transmission. Secondly, a retransmission module is established that can resend the code groups that cannot be corrected. Combined with the error detection and error correction features of the linear block code, the BER of the communication in ONoCs can be effectively reduced. Finally, we verify the effectiveness of the proposed method through simulation. The simulation results show that compared with the traditional WDM-based ONoCs, applying the proposed system to ONoCs can greatly reduce the communication BER and effectively improve the communication performance of ONoCs.
Analysis of research progress of optical fiber quantum communication multiplexing technology
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In order to realize classical-quantum signals simultaneous transmission sharing a same fiber in quantum communication, it is proposed that signals are transmitted over multiple separate channels. The channels are divided by different wavelengths, pseudo-codes, and spatial modes. Based on the development status of quantum communication over optical fiber, this paper expounds the demand of quantum communication for multiplexing technology, and introduces the basic principle and research status of three existing multiplexing technologies. In this paper, the key technologies involved in the multiplexing system based on few mode fiber are discussed in depth, and the problems in signal transmission are analyzed.
Investigation on the growth habits and optical properties of Zn-doped rapid growth KDP crystals
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Potassium dihydrogen phosphate (KDP) crystal is the only nonlinear optical material used in the Inertial Confinement Fusion (ICF) program. It has been found that metal ions have important effects on the growth and properties of KDP crystals, and zinc ion is a kind of common impurity ion in KDP raw material and crystals. In this paper, KDP crystals with different Zn2+ ion concentration were grown from aqueous solution by the “point seed” rapid growth method. The effects of zinc ion on the morphology and optical properties of KDP crystals were investigated. The results showed that the introduction of Zn2+ ions could impact the crystalline perfection and optical properties of KDP crystals.
The energy control and test in HWIL simulation system of laser jamming CCD sensors based on virtual instrument technology
Hua Li,
Yanbin Wang,
Qianrong Chen,
et al.
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According to the demands of laser energy control and test in Hardware-in-the Loop (HWIL) simulation systems for laser jamming CCD sensors effects applications, the laser propagation regulars in the system and the ways to describe laser energy simulations are provided. The basic theoretical analysis to calculate the laser energy distribution in far field and the method to achieve the simulation equipment are also discussed. Based on the Virtual Instrument (VI) technology, the ways for random phase screens formed by multiple layers of atmospheric turbulence as while as wave fronts retrieval based on a spatial Light Modulators(SLMs) set are derived. In the CCD sensors’ jamming effects experiments with different laser parameters such as repeat frequency, the lasers and their energy control equipment were utilized so as to form the distributions of laser light random phase and the undulations of laser beam intension in far field. By using the simulations system, the realization to generate different far field laser propagation effects at real time and to prove the efficiency of the laser energy control and test based on the platform of Windows+ LabVIEW+IMAQ Vision technology in simulations were experienced for CVIs. The analysis of error factors in simulation system was also provided. It is shown that the rhetorical method, devices and the analysis to simulation dynamic effects for laser propagation, which can provide the specialties of real-time, dynamic control, expansibility and can also be applied to beam quality, energy control and test in the HWIL simulation systems for laser jamming CCD sensors experiments.
Continuously bandwidth-tunable pulse generation from a SWNT mode-locked fiber laser
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The continuously bandwidth-tunable pulse generation in the SWNT mode-locked fiber laser is achieved by only tuning the intracavity polarization state. By introducing the in-line polarizer with 2-meter-long polarization maintaining fiber pigtails in a typical ring fiber laser, a bandwidth-tunable SWNT mode-locked fiber laser is constructed. The mode locker is the single-wall carbon nanotube saturable absorber, which is fabricated by optical deposition in the ~0.27 w.t % ultrasonic carbon nanotube alcohol solution. By only tuning the intracavity polarization controllers, the spectral bandwidth is continuously tuned in the range of 0.94 to 3.04 nm. We attribute the upper limit of the spectral bandwidth to the limit of the free spectral range determined by Lyot filter, which consists of polarization controllers and in-linepolarizer in the cavity. These results provide a simple way to achieve bandwidth-tunable subpicosecond pulse, which should be attractive to the applications requiring ultrafast sources with tunable bandwidth or pulsewidth.
Micro-vibration test of a reaction wheel after the mechanical test and transferring property through a shafting
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The spacecraft micro-vibration restricts the smoothness of satellite-born pointing assembles, especially for space-based laser communication, it may cause more capacity loss. A precision shafting is often the key component, connecting the satellite and the optical antenna, and transferring micro-vibration from the satellite bus to the above payload. The oscillation characteristics of the Reaction Wheel(RW) subjected to mechanical tests was implemented via pairs of liner accelerometers and acquisition system, then the micro-vibration transfer property through shafting were studied. The results showed that the RW vibration standard deviation (STD) magnified about 5 times to 30mg~50mg in time domain after the mechanical test, the FFT analysis in frequency domain showed the vibration response frequency was spurious, but the main frequency of about 430Hz and 860Hz which matched the frequency multiplication of the frequency the RW bearing balls passing the point defects in the bearing inner part. The liner acceleration and angular velocity was almost direct ratio to the RW speed, and the RW tangential vibration seemed to be more sensitive to the speed. The space used precision shafting showed perfect attenuation for a high frequency angular vibration transferring, the attenuation ratio was about 70%.
Signal analysis-based detection of train track
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Thanks to the rapid development of phase sensitive optical fiber sensing technology, it provides advanced solution to detect the track of trains. In this study, by the use of signals collected from optical fiber sensors, a time-frequency analysis method called short-time Fourier transform (STFT) is used to extract the time-frequency characteristics, based on which power spectrum can be obtained. The power spectrum with high values can be clustered via k-means, which is then used for tracking the train positions. The experimental results show that the proposed method can effectively eliminate effects caused by different subgrades on the vibration signal, reduce false alarm rate, and verify the flexibility and reliability.
Simulation study of Compton camera imaging for human head phantom proton therapy
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Prompt gamma ray (PG) imaging based on Compton camera (CC) has been proposed to realize in vivo verification during the proton therapy. However, due to the inherent geometrical complexity of Compton camera data, PG imaging can be time-consuming and difficult to reconstruct in real-time, while using standard techniques such as filtered back-projection (FBP) or list-mode maximum likelihood-expectation maximization (LM-MLEM). In addition, the imaging quality and spatial resolution of the reconstructed PG images is seriously limited by the finite energy and spatial resolution of CC, as well as the Doppler broaden effect. In this paper, we investigate the performance of in vivo verification via PG imaging with a three-stage Cadmium Zinc Telluride (CZT) pixelated Compton camera during the proton therapy for human head. We demonstrated the real-time PG imaging approach by using Monte Carlo back-projection (MC-BP) and triple events. The prompt gammas were induced by a 69MeV ~ 86 MeV proton pencil beam irradiating the human head phantom, which were simulated by using Geant4 toolkit. The results show that the reconstructions with Compton camera imaging realized nearly real-time PG imaging with a good resolution recovery, as well as provided the accurate estimation of in-vivo verification, thus demonstrating the feasibility in PG-based in-vivo proton range verification with CC.
Analysis of the topological charge by focusing vortex beams with a cylinder lens
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Vortex beams have special applications in many areas, such as quantum information processing, quantum entanglement, particles trapping and manipulation etc. A great deal of attention has been given to the research of the generating vortex beam and measuring the topological charge. This paper presents a method to measure the topological charge of vortex beams by using a cylinder Lens. Simulation and experiment results show that dark stripes appear when topological charge is non-zero, and the number of dark stripes is equal to the topological charge. Therefore our research results may be applied as a new method to analyze the topological charge of vortex beams．
Damage effect evaluation of laser weapon system
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In order to evaluate the damage effect of laser weapon system, the damage effect evaluation module of laser weapons was established based on analytical method. The evaluation indexes of the module were the minimum time required to mutilate the target and the diameter of damaged area. The influence factors of the evaluation indexes were discussed, including optical system, beam quality, tracking accuracy and atmospheric transmission. Under different distances, atmospheric turbulence and tracking accuracy, the diameter of damaged area and the minimum damage time were simulated and calculated. Therefore, the correctness of the model was verified.
Recent progress in research on TDLAS fiber optical gas sensor performance improvement
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The recent research progress of the Shandong University research group on the performance improvement of tunable diode laser absorption spectroscopy (TDLAS) fiber gas sensor is presented in this paper. The artificial absorption peak technology and the balanced ratiometric detector (BRD) technology are developed to improve the resolution of the TDLAS fiber optical gas sensor. The method for eliminating background absorption interference, the reliability study and the elimination technology of the residual amplitude modulation (RAM) are studied to improve the accuracy of the TDLAS fiber optical gas sensor. We will continue to conduct the next investigation and research in this field on the basis of existing theories and technologies.
Interconnection technology of electronic equipment in satellite cabin base on laser communication
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One of the strategic goals for the development of space technology is to achieve the mass, volume and lifetime cost of spacecraft lower than at present, which requires lightweight, miniaturization, low power consumption, rapid design and rapid integration, rapid testing and other aspects to achieve a deep level of technical breakthroughs.[1] The traditional electronic system of satellite cabin is connected by cable, which has many disadvantages, such as large volume weight, narrow band, poor anti-electromagnetic interference ability, complex network connection and low integration. If the effective No-cable technology can be adopted, the dry weight of the space vehicle can be reduced, the utilization efficiency of the payload can be improved, and the layout of the internal conductor of the space vehicle can be reduced, which not only saves the space, but also shortens the development period. Therefore, the high-speed interconnection technology of electronic equipment in satellite cabin is studied in this paper. By analyzing the characteristics of information flow and sensor distribution in the satellite, laser communication technology is adopted for high speed interconnection. Aiming at the future application, the laser communication device in satellite cabin is designed and verified in orbit, which provides an effective support for the application of No-cable satellite.
Study on performance of CPOLSK under coherent detection with pointing error in turbulence channel
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Intensity density distribution which satisfies log-normal and Gamma-Gamma distribution together with pointing error distribution and channel attenuation are considered entirely when study the performance under circle polarization modulation system with coherent detection. The closed form expression of the bit error rate (BER) and outage probability were derived corresponding to Gamma-Gamma channel. In the different turbulence parameters, the performance of circle polarization communication system were simulated and analyzed. The results shows that the performance of BER are closed approximately in Gamma-Gamma and log-normal when the channel attenuation parameter is big enough . Furthermore, the less beginning threshold SNR was derived in the region of low SNR when weak turbulence compared to Strong turbulence. However, as the threshold SNR increasing, a stronger rising slope was showed in weak turbulence channel, which makes only 3dB gaps approximate when both of them arrive at complete outage.
Joint carrier frequency offset and phase noise compensation scheme for coherent optical FBMC/OQAM systems
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We proposed a new RF-pilot based carrier frequency offset and phase noise estimation (RB-CFOPNE) scheme in offset-QAM-based filterbank multicarrier (FBMC-OQAM) systems. The performance of the proposed RB-CFOPNE with rectangular QAM modulations is evaluated by Monte Carlo simulation. The results of numerical analysis show that this method could tolerant huge frequency offset and phase noise with high speed communication system. The better performance makes it become possible for real application.
Automatic-tuning of a silicon-based seven-bit optical delay line
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We proposed a novel automatic approach for tuning automatically different delay in a 7-bit silicon-based optical delay line. The measured results of delay line by automatic tuning are also given and compared with the design values.
Relationship between angle error and image rotation of Sagnac transverse shearing interferometer
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In order to solve the image rotation in Sagnac transverse shearing interferometer, a model system is built on ray vector tracing and rotation matrix theory, as well as the theoretical imaging orientation and the actual imaging orientation with the angle error are demonstrated. Besides, the relation between the angle error and the rotation of the image body is concluded, which provides a theoretical guidance for optical alignment in Sagnac transverse shearing interferometer. Finally, an optimized optical alignment scheme is provided by the discussion of the angle error in the assembly and system-level loading process, which is also validated by optical alignment instance.
Infrared-UV dual-band image fusion camera
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With the development of the state grid, there is a great demand for equipments to detect the corona discharge on high-voltage transmission lines. The uncooled infrared image and solar-blind UV image fusion camera is supposed to achieve the purpose. Image fusion is an important method to integrate the features from images of different band spectrum into a single frame for enhanced visual perception. The image fusion camera consists of infrared channel, solar-blind UV channel, imaging processing module and display module. An image fusion rule based on the Laplacian pyramid decomposition is proposed. The fusion methodology is divided into several steps: image preprocessing, Gaussian pyramid decomposition, Laplacian pyramid decomposition, image fusion and reconstruction. The algorithm is implemented on the image fusion camera. The camera is verified to detect the corona discharge for fault diagnosis of high-voltage power system. Keywords: uncooled infrared FPA, image fusion, solar-blind UV, corona discharge
High speed TFBG-SPR sensing demodulation system based on microwave photonics interrogation
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A high speed TFBG-SPR sensing demodulation system based on microwave photonics interrogation is proposed theoretically. The wavelength shifting of the SPR envelope in optical domain is converted to the microwave pulse shifting in time domain. The RI resolution is improved by one order of magnitude compared with wavelength demodulation, and the sensing speed is as high as 40 KHz.
Oxygen-deficiency and OH changing of fused silica induced by the 248nm pulsed laser
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The Oxygen-deficiency and the content and structure of OH had been proved to lead to various laser-irradiated damage threshold. In order to get the principle, we detected the changing tendency of the the Oxygen-deficiency and OH content after the irradiation without damaging. The results showed that the increasing of the Oxygen-deficiency and decreasing of the OH .Which is the result of the structure-collapsing and the effect to delaying the collapsing by Oxygen-deficiency and OH.
Research on underwater high-speed blue-green optical communication technology based on blue LD array
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In underwater wireless optical communication (UWOC), one of the key technologies is to generate high-speed communication signal for transmitter. In this paper, we designed such transmitter based on laser diode (LD) arrays, which is composed of three LDs with central wavelength 450nm. The modulation format is non-return-to-zero on-off keying (NRZ-OOK) with data rate up to 50Mbps. Using such transmitter, we established a point-to-point underwater wireless optical communication link in an experimental tank with 20m length, 20m width and 14 depth. The experimental results show that the maximum error-free data rate of the system can reach 50Mbps with 10.7m transmission distance, while the maximum error-free transmission rate is 30Mbps with 14.7m transmission distance. These results verify the feasibility of the LD-based modulation scheme for high-speed UWOC applications.
The properties of zirconia during the fused silica polishing process
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In this paper, the polishing properties of the zirconia slurry on the fused silica were studied, comparing with the effect of the ceria polishing. The polyurethane without dopant was applied as polishing pad. The experiment results show that it is easier to produce surface scratches when compared with ceria polishing owing to the high Mohs hardness of zirconia. The surface roughness(Rq) of the workpiece was less than 1nm after polishing with submicron size polishing slurry and suitable polishing pad. The R-on-1 test of 355 nm laser-induced damage threshold for fused silica show that zirconia polishing performance is 3.02% higher, however the exposed subsurface damages with HF etching were more than ceria polishing.The subsurface defect density is 0.10def/cm2 (@1μm)with ceria polishing and 1.19def/cm2 (@1μm)with zirconia polishing. Based on the fine polishing performance and abundant resources in nature, the zirconia slurry may be an alternative for fused silica polishing in prospect with the appropriate technological solution.
Design of high-index-contrast grating as quarter-wave plates
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This paper focuses on the quarter-wave plate design based on subwavelength high-index-contrast grating (HCG). The relationship among the equivalent refractive index of the HCG, the duty cycle of grating and the incident wavelength was obtained with the theory of effective medium and rigorous coupled wave analysis. By selecting the parameters and using the iterative algorithm proposed in this paper, quarter-wave plates with excellent performance can be obtained.
Routing algorithms with efficient resource utilization for LEO satellite networks
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Recently, a series of researches have been emphasized on developing advanced satellite networks, mostly because of its advantage in providing spaced-based global communication service. But most of these work prefer to focus on the timevarying topologies, large delays and intermittent connections of satellite networks. However, there is another issue worthy of attentions, i.e., the scarcity and preciousness of satellite resources, owing to the shortage of orbit resources and the high cost of launching a satellite. Therefore, it is significantly important to consider the efficient utilization of resources during designing routing strategies for satellite networks. In this paper, we propose two routing algorithms to optimize the number of used inter-satellite links, which will directly improve the bandwidth utilization and save resources for LEO satellite networks. The basic idea is to reduce the number of links used by lower-priority traffic through scheduling them to links used by highest-priority services, and simultaneously introduce the load balancing strategies to control the aggregation of network flow. Simulation results show that with the price of little longer latency and load unbalancing, our algorithms can effectively decrease the total number of used links, and thus improve the resource utilization and save energy for satellite networks.
An easy produced optical fiber SERS sensor
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Surface Enhanced Raman Scattering (SERS) is typically observed with the substrate in a liquid medium and it has been proposed as a promising technique for detecting low levels of pollutants in liquids. The design and fabrication of an optical fibre SERS sensor based on Au nanoparticles (Au-NPs), which is self-assembly immobilized onto the end surface of an optical fibre is described. Two toxic materials, Rhodamine 6G (R6G) and crystal violet were analysed using this optical fibre SERS sensor combined with portable Raman spectrometer. Our proposed fabrication and analytical method offers a rapid, cheap and disposable trace detection capability for toxic materials in the field.
A new algorithm based information anti-destruction storage and anti-eavesdrop distribution on satellite communication system
Juan Li,
Yu Wen,
Jiong Liu,
et al.
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In view of the problem that the satellite communication system's satellite link and inter-satellite link were eavesdropped easily by the enemy, the technical idea of fountain coding and network coding was used to study the system framework of information distribution storage and distribution of satellite communication system. Based on this, a new anti-destruction storage and anti-eavesdrop distribution algorithm for satellite communication system was proposed, which realized the confidential storage and security distribution of information , as well as the anti-destruction storage and anti-eavesdrop distribution of information.
Dual-energy CT technology and spectrum estimation algorithm
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Dual-energy X-ray computed tomography (DECT) can accurately reconstruct the effective atomic number and electron density distribution. Currently, it is an effective material identification technology for security inspections. X-ray energy spectrum estimation plays an important role in dual-energy CT. First, the reconstruction principle of dual-energy CT is introduced. Second, based on common transmission data estimation method, this paper focuses on spectrum estimation using CT image reprojection technology. By scanning the cylindrical model which contain two materials and using the maximum expectation algorithm (EM) to estimate the X-ray energy spectrum distribution, the simulated spectrum of Monte Carlo was used as the initial value of iteration. This method improves the accuracy of dual-energy CT reconstruction algorithm.
Calculation of the omnidirectional nonlinear optical coefficients of ReCOB (Re = Y, Gd and La) crystals
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Almost all attention has been paid to the effective nonlinear coefficient along the direction of phase matching, so this paper calculated the omnidirectional effective nonlinear coefficient of ReCOB single crystals by computer out of interest. The results showed that the distribution of the first and second quadrants of omnidirectional |deff| presented multi-peaks surface divided by three “valleys” which were made up of a series of minimum values. The variation of d32 and d13 had more significant impacts on the distribution of omnidirectional |deff| than the other coefficients and the variation of wavelength had negligible influence on that. A broadband wavelength range about 6 nm could achieve efficient frequency conversion simultaneously within the deviation being less than 2 degrees during a type-I DFG process in YCOB crystal. These results could provide valuable guidance for the selection and utilization of ReCOB crystals.
A denoising algorithm for terahertz time domain spectrum based on lifting wavelet transform
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Terahertz time domain spectroscopy has been widely used in tumor detection, chemical analysis and nondestructive testing. However, the measurement errors of terahertz time domain spectrum frequently occur because of vibration of experiment instrument platform or temperature and humidity changes. Lifting wavelet transform based on different wavelet basis functions was applied to the denoising of terahertz time domain spectrum of PTFE. The denoising results were compared with denoising results of wavelet soft threshold method. The wavelet soft threshold method got a highest signal to noise ratio (SNR) of 58.75 dB and a least root mean square error (RMSE) of 3.56*10^ (-5), while lifting wavelet transform method achieved a highest SNR of 60.69 dB and a least RMSE of 2.85*10^ (-5). These results imply that lifting wavelet transform performs better in terahertz spectrum denoising than wavelet soft threshold.
A serrodyne frequency translator with wide-band and high precision based on paralleled PM and DP-MZM
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A wide-band microwave frequency shifter with high precision has been proposed and constructed based on paralleled PM and DP-MZM. PM is used to control the optical carrier phase that is driven by a sawtooth wave with a center frequency, while DP-MZM is used to generate a single-sideband suppressed carrier modulation. Results show that the frequency shift of kHz~GHz can be realized with the microwave carrier suppression of better than 50dB.
A wideband optical channelized receiver based on coherent optical frequency combs and Fabry-Perot filter
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An optical channelized receiver (OCR) with a novel structure based on two coherent optical frequency combs (OFCs) and a Fabry-Perot (FP) filter has been proposed. Input wideband signals are multicasted in all optical channels by modulating one OFC. Then, different sub-frequency bands in all optical channels are filtered out by the FP filter. Finally, the sub-frequency bands are directly converted to intermediate frequency (IF) via coherent optical heterodyne with the LO provided by another OFC. Experiment results shows that the OCR works in X band with 8 channels, and the bandwidth of each channel is 500MHz, which means the instantaneous bandwidth of the OCR is 4GHz. The max power fluctuation between different channels is 4dB, which can be improved by adding proper attenuators to certain channels. The spurious free dynamic range (SFDR) of all channels is above 44dB under noise bandwidth of 1MHz, which equals to 84 dB·Hz2/3.
Crack depth uniformity control techniques for large scale fused silica optics in grinding process
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In order to improve the overall efficiency of machining and the defect quality of large aperture fused silica optics, it’s necessary to strictly control the crack defects and their depth uniformity in the first grinding process. Firstly, the morphology of three typical defects affecting the uniformity of crack depth was analyzed, which were scattered superficial sand holes, continuous linear defects and dotted linear defects. Then according to the morphology, the causes were investigated and the control techniques were proposed. The scattered superficial sand holes were caused by the large size glass powder, the diamond particles dropped from the grinding wheel and other foreign body impurities in the grinding fluid, which had been squeezed into the surface of the element by the grinding wheel. Through the clean filtration of grinding fluid, the quantity of such defects could be effectively reduced. The continuous linear defects were caused by stress concentration at the two sharp edges of the grinding wheel. Arcing the two sides of wheel could reduce the machining stress at the edges and avoid the occurrence of continuous linear defects. The dotted linear defects were caused by the stress concentration of the grooves on the surface of the wheel during grinding. After optimizing the dressing parameters to reduce the dressing force and avoid the grains of dressing wheel being embedded into the grinding wheel surface, all the grooves on the wheel surface and all the dashed line defects on the element surface disappeared practically. At the last, after integrating all the above control techniques, the grinding experiment of large scale fused silica optics was carried out. The scattered superficial sand holes, continuous linear defects and dotted linear defects on the surface of element after grinding were obviously alleviated. The crack depth of the whole aperture was between 4μm and 7μm. All the results indicated that the control techniques were efficacious.
Tunable optical beam-forming network for millimeter wave using VODL
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Broadband, free beam squinting and large scanning angle are essential for many applications. In views of these requirements, a tunable optical beam-forming for millimeter wave is proposed and demonstrated experimentally based on dispersive prism and variable optical delay line (VODL). Experiments are implemented with 1×4 antenna array operating at Ka band. Two beams are produced simultaneously for amplitude comparison direction finding. By tuning the relative delay of four VODLs, the beams can sweep across -30°~30°.
Influence of grinding force on aspherical small-scale waviness uniformity based on parallel grinding
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Aiming at the problem of poor uniformity and large amplitude of aspherical small-scale waviness caused by grinding aspheric surface by traditional grating parallel grinding technology, in this paper, the reasons for the poor uniformity of aspherical small-scale waviness in traditional grating parallel grinding technology are analyzed from the perspective of grinding force. Considering the influence of the uniformity of the grinding force during the grinding process on the aspherical small-scale waviness, an up-grinding grating parallel grinding method and a down-grinding grating parallel grinding method are proposed. The effects of the grinding force of the two grinding methods on the aspherical small-scale waviness uniformity are analyzed experimentally. Finally, among these three grating parallel grinding methods, the aspherical small-scale waviness obtained by the down-grinding grating parallel grinding method is the most uniform and the waviness amplitude is the smallest, the waviness amplitude is less than 2μm.
Circular polarization modulation technology and its application research in free-space optical communication
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Theory and experimental results show that the state of the circular polarization of laser changes little in the atmospheric channel, and circular polarization modulation technology can improve the performance of free-space optical communication systems. This article starts from the principle of circular polarization modulation technology, introduces several common circular polarization transmission system structure, and then briefly describe its application and research direction in the future.
Polishing pad aging studies on computer controlled optical surfacing finishing for large-scale sapphire optical window
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Polishing pad becomes aging after finishing for a while, by reason of friction and wear, or polishing particles deposition, which will reduce polishing effects, increase polishing effects and make a low polishing quality. When the ultra-hardness of sapphire material needs high pressure and high rotate speed parameters, which will accelerate aging of polishing pad. When large scale sapphire optical window is finished by computer controlled optical surfacing (CCOS) method, the polishing pad aging problem is an important confinement factor for high quality of polishing. In this paper, we confirmed the stable polishing period and aging time node of pitch pad and polyurethane pad by polishing experiments. For pitch pad, time aging nodes are between 50min and 75min with polishing pressure 0.1Mpa and 0.2Mpa and between 25min and 50min with polishing pressure 0.4Mpa. For polyurethane pad, the time aging nodes are over 75min with polishing pressure 0.1Mpa and 0.2Mpa and between 50min and 75min with polishing pressure 0.4Mpa. The aging time of polyurethane pad is later than that of pitch pad. Increasing polishing pressure will help increase material removal rate, but will accelerate aging of polishing pad
High-contrast dark-field imaging method for detecting optical surface micro-defects
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Surface and subsurface defects significantly impact on the performance of optical components, especially on high-power laser optics, of which the damage threshold will be lowered by defects. Therefore, it is required to detect defects in optical manufacturing. In this paper, a novel dark-field microscopic imaging method, Circular-Aperture Microscopy (CAM), is proposed for defect detecting of optical surfaces. In CAM, an illuminating ray transmits through the optical surface and is blocked by a small obscuration attached on the objective. The scattered light by the defect propagates through the circular aperture formed by the obscuration, and forms a high-contrast image on the camera. Because the illuminating ray is blocked, CAM is a dark-field imaging method. Since the illumination light is incident perpendicularly to the surface, there is no shadow effect in CAM. The imaging results of scratches and pitted standard comparison plates, resolution transmission test plates, SiO2 suspensions and other samples show that CAM has the advantages of simple principle, high contrast, high resolution, and high precision, It can provide an effective method for defect detection and control in optical surface manufacturing.
Design of motion equations for dynamic support structure of space-on-orbit segmentation mirror
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In order to realize the on-orbit expansion of the space segmentation mirror and the fine adjustment of the mirror surface, a dynamic support mechanism is designed. And its adjustment mechanism is analyzed. Firstly, the dynamic support mechanism is designed and modeled. Then, the inverse calculation of the support mechanism pose is analyzed. Finally, a finite element analysis of the established model is carried out, and compared with the experimental results. The results show that the space segmentation mirror has the ability to be assembled into a large-caliber telescope on orbit and to ensure image quality.
Research on stability of gas monitoring system based on TDLAS
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During industrial process of gas monitoring, gas pumps are typically used for extract gas dynamically. In order to improve the response time of system, high flow rate pumps are used to draw gases under detection into the gas cell, and therefore, the airflow during monitoring has an impact on system stability. In this paper, we firstly optimize the design of absorption cell through software simulation, so as to improve the airflow stability at high flow rate. And secondly, the normalization algorithm is used to try to suppress the influence of airflow fluctuation on the stability. Finally, we built a dynamic methane measurement system, and the results of normalized and un-normalized concentrations over time were provided for comparison, respectively. The experiment results show that under the flow rate is 34L/min, the response time is 1.2s, and after normalized treatment, the stability is improved from 2.68ppm to 0.64ppm (1σ).
The in-situ laser induced damage test of fused silica optics with different HF etching depth
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The in-situ monitoring of subsurface defects and laser damages initiation using high resolution on-line microscope is performed on medium aperture fused silica optics manufactured by different procedures to investigate the specific damage precursors. The digital camera, Nomarski microscope and white light interferometer are used to characterize the subsurface defects. With shallow HF etching depth, the laser induced damages are mostly initiated on indents or invisible defects under the fluence of 8~10 J/cm2@355nm. The laser induced damages initiated on indents is gradually decreased with the increased etching depth and the laser induced damage density is also decreased. Besides, decrease of the indents by optimizing the polishing process could also make the laser induced damage density sharply decrease. These results prove that the indents are important damage precursors and the laser induced damage performance of fused silica optics could be substantially improved by decreasing the indents or deep HF etching.
Experimental study of the air-knife thermal control system for a large-aperture primary mirror
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The thermal induced effect errors including the surface distortion of heated mirror and micro-thermal turbulence fluctuation at the optical surface dramatically degrade the image quality of the telescope. To address the problem, we have proposed an air-knife system consisting of an annular flushing subsystem and a central sucking subsystem and reported its simulation analysis. This paper presents the detailed experimental performance of the air-knife thermal control system. The scaling experiment is conducted in a thermo-cycling experiment room with different environmental conditions, where the temperature fluctuations and wavefront perturbation of the scaling mirror can be accurately measured. It is shown from the experimental results that the approximately laminar forced air flow at the optical surface does blow away the turbulence fluctuation and not induce novel low order wavefront aberrations. Meanwhile, the air knife system contributes to the stability of the thermal boundary layer and enhances the convective heat exchange between mirror and air around. As a result, the air-knife system significantly decreases the surface-to-air temperature difference and improves the image quality with a thermal response. Furthermore, it is found that thermal control efficiency is less significant with the increase of the air intake flow or the decrease of the surface-to-air temperature difference. The scaling experiment results demonstrate the practicability of the air-knife thermal control system for large-aperture primary mirror.
Fabrication and damage characteristics of low stress HR films for femtosecond laser system
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With the development of femtosecond laser system, the laser damage threshold of optical components becomes more important. Meanwhile, in order to obtain better laser beam quality and avoid wavefront distortion caused by optical components, more stringent requirements are put forward for the surface shape of the coated surface of mirrors. HfO2-SiO2 high reflective films were fabricated by e-beam thermal evaporation method. Internal stress of the multilayer dielectrics was modulated by changing the design of films and coating process. Finally, the film with an absolute internal stress less than 100MPa was obtained. The laser damage characteristics of the films at 35fs, 1000Hz were studied, and the damage mechanism was analyzed.
Influence mechanism of plasma cleaning and ion beam figuring on the intrinsic surface of fused silica
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The laser damage threshold of fused silica optics is affected by the surface/subsurface defects in optical fabrication and is related to surface contamination. In this paper, the evolution of surface roughness and photothermal weak absorption of fused silica treated by plasma cleaning and ion beam figuring (IBF) is studied. The results show that plasma cleaning has a certain change on the surface roughness of fused silica, while the change of photothermal weak absorption depends on the initial surface quality. The surface roughness of fused silica has a certain regularity after ion beam figuring, and the photothermal weak absorption is basically consistent with the initial.
Receiving principles and experimental test of several commonly used methods for laser ultrasonic thickness measurement
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Laser ultrasonic technology has become an effective method and technological means for thickness measurement of metal materials nowadays. Generally, common method for receiving laser ultrasonic signals has piezo-electric transducer (PZT), laser interferometer and electro-magnetic acoustic transducer (EMAT). In this paper, the receiving principles of three kinds of receiving methods are given, and the diagrams of three methods with different thickness obtained by experiments are drawn. Each method has its own advantages and disadvantages, so appropriate receiving method should be selected according to actual needs for engineering application.
Processing technology of magnetorheological finishing for large-aperture optical components
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Magnetorheological finishing (MRF) is a deterministic optical element polishing method that achieves material removal by means of the sheared and rheo-logical behavior of magnetorheological fluids. To realize high precision fabrication of large-aperture optical components, MRF technology had been explored in this paper. The main factors affecting the removal efficiency were investigated by orthogonal experiment. It indicated that the influence of the immersion depth and the thickness of ribbon on removal efficiency was more remarkable than the other parameters. The process of MRF machining component is established. Finally, the 590mm × 400mm plane optical element are manufactured using the MRF, and the result are very good.
Simulations study of segmented mirror coarse phasing using two-dimensional dispersion fringe sensing technology
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Two-Dimensional Dispersion Fringe Sensing (TDDFS) is an efficient method for coarse phasing of segmented mirrors. Modeling and simulations based on double-aperture diffraction are used to study dispersion fringe in two directions. In the dispersion direction, the nonlinear least squares fitting method is used to extract the piston error. The theoretical capture range is ±96μm which is verified compared with the simulation results, and the detection accuracy can be reached to λ/10. However, the nonlinear least squares fitting method cannot effectively detect piston errors within one wavelength. In the diffraction direction, the principal maximum extraction method is used to measure the piston error, which is suitable for the piston error detection with a small range within one wavelength. In order to reduce the influence of the extraction error of the center line, we propose a corrective method. The results show that the accuracy of the modified principal maximum extraction method can reach 30nm. The two methods can effectively meet the requirements of the piston detection of the large-aperture segmented mirror telescopes.
Study of system matrix based reconstruction for uncertain scanning track CT
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Computed Tomography (CT) has been an irreplaceable method of non-destructive testing in heavy industry and architectural design for a long time. Although, in recent years, a new CT technology with high resolution and extensive applicability for in-situ large-scale structure inspection of concrete has been applied in production. The complexity of the scanning environment and mechanical vibration during the in-situ press loading can result in artifacts on CT image. To solve this problem, a reconstruction algorithm based on system matrix was implemented to reduce of influence caused by track jitter and undefined scanning track. A simulation experiment was performed to verify the algorithm. The result shows the feasibility of the proposed reconstruction algorithm.
A comprehensive effect evaluation method of pattern painting camouflage based on entropy weighted similarity
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Aiming at the problems existing in the effect evaluation of pattern painting camouflage, such as evaluating indicate simplification and nonobjectivity, this paper proposes a new method for effect evaluation of pattern painting camouflage based on entropy weighted similarity. According to the object and purpose of pattern painting camouflage assessment, five characteristic evaluating indicators of target image and its background, namely, hue, brightness, shape, texture and speckle, are selected synthetically, and the weight of each evaluating indicator affecting the whole evaluation result is determined by using entropy weight method. The different patterns of painting camouflage with some specific backgrounds are selected for comprehensive evaluation, meanwhile, these camouflage painting patterns are evaluated by the classic grey clustering decision algorithm, and finally the evaluating results of two methods are compared. The results show that the conclusions obtained by the two different evaluation methods are consistent and support mutual verification, which indicates that the proposed method in this paper is feasible and effective for the effect evaluation of pattern painting camouflage.
Experimental study on combustion-driven hydrogen bromide (HBr) chemical laser
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An experimental study of combustion-driven HBr chemical laser based on D2/NF3 combustion was carried out. The exotherm of the reaction system was analyzed, and the thermal blockage issue of supersonic flow was solved by adjusting the buffer coefficient ω. By optimizing the laser operating conditions, a maximum HBr laser output of 141W was obtained, with the primary laser lines being HBr P1(5) , P1(6) , and P3(6).
Continuous-wave and passively Q-switched c-cut Nd:CTGS laser
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Diode-pumped continuous-wavelength and passively Q-switched laser with a novel Nd:CTGS crystal were reported. In continuous-wave operation, maximum output power of 3.5 W was obtained with slope efficiency of 38.6%. With Cr4+:YAG as the saturable absorber, passively Q-switched 1065 nm laser with high power and high energy were demonstrated. Maximum output power was 1.6 W with slope efficiency of 21.2%. Minimum pulse width of 8.4 ns was obtained with pulse repetition rate of 33.1 kHz, corresponding to maximum pulse energy of 45.7 μJ and peak power of 5.4 kW.
Correction of gas concentration based on tunable diode laser absorption spectroscopy in different temperatures
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Tunable diode laser absorption spectroscopy (TDLAS) is often used to detect the industrial processing gas component, but the concentration measurement in the field is easily affected by the surrounding temperature. Firstly, the effect of temperature on absorption spectrum was analyzed. Taking methane as an example, DFB laser with 1654nm was used to collect the concentration under temperature from 253K to 323K (with the interval of 10K for each point) based on WMS method. The results showed that the maximum relative error was 25%. Based on the experimental data, the correction formula of second harmonic full waveform was fitted, and the gas detection system with temperature compensation was constructed at the same time. The experimental results illustrated that the maximum relative error under the same test conditions was reduced to less than 5%, and the detection accuracy were significantly improved under variable temperature environment, which provided the guarantee for TDLAS online monitoring and broadened the use scenario of the technology.
True zero-order crystal wave-plate made of ADP crystal
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This paper shows a novel design for a true zero-order wave-plate to introduce an accurate phase retardation with a big birefringent crystal. The true zero-order wave-plates can be processed with different angles deviating from the crystal’s axis, and the thickness could be selected from millimeter to centimeter order, which increased the mechanical strength greatly. The true zero-order wave-plates were made of NH4H2PO4 (ADP) crystal, including half wave-plate (HWP) and quarter wave-plate (QWP). When the cutting angle θ is 4o, the thickness d of 1064 nm TZ half wave plate (HWP) is 2.75 mm. At the room temperature (25°C), its extinction ratio as the polarization rotator reaches 1000:1 at 1064nm by using spectroscopic method. With ADP-QWP, a 18.6 ns pulse output of Q-switched Nd:YAG laser (1064nm) is successively realized. When the static energy is 160 mJ, the dynamic energy reaches 113 mJ. The above contents provide not only good references for wave-plates fabrication of other birefringent crystals, but also more potential applications in largediameter optical systems such as ultra-high power laser, high resolution inspection equipment and astronomical observation equipment with a large-diameter ADP wave-plate.
F-P interference optical fiber pressure temperature composite sensor based on sapphire MEMS chip
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A Fabry-Pérot (F-P) interference optical fiber pressure temperature composite sensor based on all sapphire substrate is researched and fabricated for high temperature applications. Micro-electro-mechanical systems (MEMS) technology and atomic direct bonding technology are used to fabricate F-P pressure temperature composite sensing cavity and then packaged to form core components of the sensing probe. The high-temperature fiber is used as transmission medium of optical signal. Length of pressure sensing cavity is 104.5μm, length of temperature sensing cavity is 434μm. Sensing characteristics test on chip is carried out, and pressurization tests on sensor from room temperature to 400℃ are performed. The experimental results show that pressure chip of 5MPa can distinguish pressure of 0.17kPa, the relative resolution can reach 33ppm, and temperature cavity length fluctuate ±0.1nm within 678s, which is equal to 0.05℃ temperature error. Performance index of sensor in temperature range of the whole is good. This research provides strong support for extrinsic optical fiber sensor based on sapphire composite F-P cavity using for precise and stable pressure and temperature measurement in high temperature environment.
The effect of modulator bias point on harmonic suppression of MWP based RF channel
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Microwave photonic (MWP) based radio frequency (RF) channel is usually composed of three parts: microwave pre-processing part, electro-optical interconversion part and microwave post-processing part. The nonlinearity of active components causes serious harmonics at the output of MWP based RF channels. This paper mainly analyzes the harmonic distortions produced in the external-modulated optical transmission link and studies the variation of output harmonic power in the RF channel by changing the modulator bias point. According to the experiment, it is verified that the second harmonic can be effectively suppressed when the modulator is biased at high power point.
Impulse coupling performance of laser ablation GAP in vacuum environment
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Energetic working fluid polyazide glycidyl GAP, has attracted more and more attention in the field of laser ablation micro thruster[1-3] because it can not only absorb and utilize laser energy, but also fully release its chemical energy and participate in the process of impulse formation. In order to explore the impulse coupling characteristics of solid GAP in vacuum environment, infrared dyes with different mass fraction were doped as absorbent. In a vacuum chamber with a pressure of 30 Pa, a 1064 nm Nd: YAG laser was used to test different laser energy modes (transmissive and reflective) for different thicknesses and different doping concentrations at different laser energy densities. The results show that the doped infrared dye can not significantly change the absorption threshold of laser energy by GAP, but significantly increases the deposition of laser energy in GAP. The doping concentration has a great effect on the coupling performance of the pumping amount within a certain concentration range. When the doping concentration is 5%, the momentum coupling performance of laser ablation GAP is optimal. The thickness of the GAP with the best impulse coupling performance is related to the doping concentration. The higher the concentration, the smaller the thickness of the GAP with the best ablation performance. When doped with infrared dye, GAP exhibits the body absorption characteristic of laser energy, which follows the injection mechanism of “first absorbing laser energy first injection”, so the reflective ablation mode exhibits better propulsion performance.
The mid and low-spatial frequency error control technology research during the process with ion-beam figuring in large aperture standard mirror
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By the ion-beam figuring machine IBF600, a 630 mm aperture fused silica flat standard mirror was polished up to surface PV value 38.9 nm and RMS 6.556 nm in low frequency error, during the same time ,the mirror’s mid-spatial frequency(spatial frequency band 2.5 mm~33 mm) wavefront RMS error converged to 1.502 nm from initial value 2.022 nm.During the process, two removal functions were used in the simulation after parameter optimization. According to the residual error map, we choose the appropriate removal function and calculate the dwell time, finally we successfully attained the optical acquirements of the standard mirror in both low and middle frequency error, this high middle frequency.
Metal artifact reduction based on fully convolutional networks in CT image domain
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Metal objects inside the field of view would introduce severe artifacts in x-ray CT images, which would severely degrade the quality of CT data and bring huge difficulties for subsequent image processing and analysis. Correction of metal artifacts has become a hot and difficult issue in X-ray CT. In recent years, deep learning has rapidly gained attention for employment on image processing. In this study, we introduce a Fully Convolutional Networks (FCNs) into the MAR in image domain. The network reduces metal artifacts by learning an end-to-end mapping of images from metal-corrupted CT images to their corresponding artifact-free ground truth. The network takes the metal-corrupted CT images as the input and takes the artifact-free images as the target. The convolution layers extract features from the input images and map them to the target images, and the deconvolution layers use these features to build the predicted outputs. Experimental results demonstrate that the proposed method can well reduce metal artifacts of CT images, and take a shorter time to process the images than traditional method.
Impact of process parameters on super-smooth surface of the fused silica created by magnetorheological finishing: simulation and experimental study
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To achieve the super-smooth surface of the fused silica via using the magnetorheological finishing (MRF) technique, the synergistic effect of the rotational speed, viscosity, and working gap is well investigated. According to the pressure field simulation based on the two-dimensional Reynold equation, the working gap is of remarkable importance to the surface roughness among three parameters. Furthermore, such result is also revealed by the MRF experiment. Accordingly, the optimized process parameters are identified, and the final surface roughness is achieved as low as 0.22 nm.
An investigation on the material removal mechanism of abrasive-free jet polishing for KDP crystal
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Potassium dihydrogen phosphate (KDP) is the irreplaceable nonlinear single crystal as optical frequency conversion and electro-optical switch in inertial confinement fusion (ICF) laser system. Based on the water solubility characteristics of KDP crystal, we propose an abrasive-free jet polishing (AFJP) method for KDP crystal with the purpose of improving surface quality without the embedding of particles. According to the AFJP experimental results, the jet spot generated by AFJP is of an approximately Gaussian shape. The feasibility of this approach has been studied through spot experiments. And the material removal mechanisms can be divided into contact removal and slipping removal.
Ultra-narrow linewidth Brillouin-erbium fiber laser pumped by distributed feedback fiber laser
Haifeng Qi,
Zhiqiang Song,
Weitao Wang,
et al.
Show abstract
An ultra-narrow linewidth fiber laser in a Brillouin ring cavity structure pumped with a distributed feedback fiber laser is presented. A total cavity length about 10m is constructed to satisfy the single longitudinal mode working condition. As a part of the ring cavity, a 3m-long Erbium doped fiber pumped with a 980nm laser diode provides an additional linear gain for intra-cavity Brillouin laser. After an intra-cavity polarization control, a single longitudinal mode Brillouin laser with an unique polarization is achieved and its linewidth is measured and deduced to be narrower than 100Hz. The threshold for single longitudinal mode operation is about 20mW distributed feedback fiber laser and 50mW 980nm pump. A maximum laser output power of over 15mW can be obtained for a maximum 980nm pump power of 250mW.
A novel 272Gb/s QPSK coherent optical communication scheme for the integration of satellite communication and ranging
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The optical frequency comb(OFC) technology is suitable for precise dimensional metrology for its low fractional uncertainty, while coherent optical communication has the advantages of high receiving sensitivity and capacity. To combine the benefits of both technologies, a novel single-polarization 272 Gb/s coherent optical communication scheme employing four wavelengths is proposed and evaluated. By introducing a 100MHz-reption rate home-made mode-lock fiber laser and optical band-pass filters, the 150GHz-bandwidth OFC signal is generated and transmitted with the coherent optical signals. By the demodulation of the real-time coherent optical receiver, the bit-error-rate (BER) results of four wavelengths are obtained. The proposed scheme provides a simple way to achieve wideband communication and the OFC signal transmission, which can be attractive for the application of onboard integration of communication and ranging.
Neutron radiography study of water spontaneous imbibition in unsaturated sandstone
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The spontaneous imbibition of water in variable saturated porous media is a common phenomenon in various geotechnical applications. The relationship between the traveled distance of wetting front and imbibition time can be characterized by the sorptivity however, few researches have been carried out to investigate the sorptivity model in the spontaneous imbibition process. In this paper, based on the fractal dimension of pore mass and the formula of total flow rate of cross section of medium without considering gravity, a model was derived to calculate the sorptivity of sandstone. To validate the model, quantitative data on the imbibition of water in the matrix of unsaturated sandstone were obtained by neutron radiography a powerful imaging tool to research the dynamic water imbibition behaviour in rocks. The consequences display that there is the obvious linear relation between the traveled distance of wetting front and the square root of imbibition time in four monitoring lines and the linear coefficient is regarded as the experimental value of the sorptivity. Compared the mean of the experimental value, the theoretical value computed by the sorptivity model can reflect the experimental value to a large extent and, thus the sorptivity model can be applied to estimate the sorptivity of sandstone in the process of spontaneous imbibition.
Application of distribute acoustic sensor technology in oil and gas exploration
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Distribute acoustic sensor technology (DAS) is applied to oil and gas exploration. The advanced achievements of international DAS-VSP technology were investigated. The VSP data of DAS and conventional detectors were acquired at same source points. After data analysis, processing and application, the DAS-VSP records and imaging profiles of high signal-to-noise ratio and resolution were obtained. Finally, the advantages and research direction of DAS-VSP data in oil and gas exploration are analyzed.
Fabrication and test of novel fiber Bragg grating based humidity sensor
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Optical humidity measurement is essential in current industry, especially in environment with adverse electromagnetic field and strong corrosion. This paper focus on the fabrication and test of a novel fiber bragg grating based humidity sensor. The sensor is fabricated by uniformly coating humidity sensitive material on fiber bragg grating. The sensing characteristic test of the sensor shows: the wavelength shift following humidity is linear; the minimum response time of the 2-layer coated sensor is 10 s with sensitive coefficient can be controlled by changing coating time; hygroscopic hysteresis of 3-layer coated sensor is 2.7`%RH. Therefore, the sensor is promising to be used to meet the quick response and in vivo measurement demand in industry.
A near ground infrared weak and small target detection algorithm based on ILCM saliency detection and dual-band image fusion
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Aiming at the drawback of single sensor detection, the multi-sensor fusion technology is used to study the near ground infrared weak and small target detection based on fuzzy integrated decision-level image fusion. Firstly, the ILCM (improved local contrast mechanism) operator is used to calculate the infrared image saliency by using the image subblock instead of the pixel in contrast calculation. Then, the significance threshold ROI (region of interest) is introduced to eliminate the influence of the background, and the fusion region is divided by the region correlation mapping. Finally, the target fuzzy membership degree is calculated for the single sensor image according to the proposed RM (region matching) and FM (fuzzy membership) fuzzy features, and the infrared target is obtained by the fuzzy synthesis method. Experiments show that the proposed algorithm has good robustness and strong anti-interference ability for the infrared weak and small target detection in complex near ground background, and it has better target detection effect than single sensor.
Influence of electro-optical crystal flatness on indirect modulation signal for underwater blue-green laser communication
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Indirect modulation with electro-optical crystal is a useful way to generate optical signal for underwater blue-green laser communication. However, as crystal surface is not strictly flat in practical application, light intensity distribution in the cross section is non-uniform, which would affect extinction ratio of modulated signal and system performance. In this letter, we study this issue with Monte Carlo method. The result shows that with the increase of crystal flatness, extinction ratio is decreasing dramatically, and it should be smaller than 0.78μm in order to make the extinction ratio greater than 10dB while 0.25μm for 20dB, 0.08μm for 30dB, and 0.025μm for 40dB.
Research on super-resolution reconstruction algorithm of infrared images of compressive coded aperture
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To address the problem of low resolution of infrared imaging system, this paper combined compression coded aperture imaging to study infrared imaging, which can break through the imaging limit of infrared detectors and achieve super-resolution imaging. Compression coded aperture imaging mainly utilizes the sparsity of images, and solves mathematical models through reconstruction algorithms and reconstructs target images with high resolution. Reconstruction algorithm is a vital procedure in the process of compression coded aperture imaging, which determines the reconstruction accuracy and reconstruction speed of the image to some extent. In this paper, the existing compression coded aperture imaging reconstruction algorithms are classified and summarized. In the infrared imaging, the typical algorithm is simulated and verified, which can provide reference for future research in the field of infrared imaging.
Technical research on fabricating steep off-axis aspherical mirror based on infrared interferometric testing
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This article mainly take the research on the technique of fabricating a steep off-axis aspherical mirror based on infrared interferometric testing. In the stage of asphercal shape grinding ,we take use of an infrared interferometer to test the aspherical surface error rapidly, along with the arm-swinging polishing method and choose the appropriate processing parameters according to the testing results. After more than twenty times polishing and testing circles ,the off-axis mirror’s wavefront error converge to PV≤5 λ,RMS≤1 λ(λ=632.8nm),this surface map is suitable for the final sub-surface polishing. Through these research and experiments, we have verified the applied advantage of infrared interferometric technique in fabricating steep off-axis aspherical mirror. This technology is also very useful in the processing other types of large-scale aspherical mirrors.
Fiber Bragg grating sensor for motor transient torque measurement
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In this work, a novel fiber Bragg grating (FBG) sensor is designed for the measurement of motor axis transient torque. The sensing mechanism of FBG is introduced, the mathematical relationship between applied torque and Bragg wavelength is analyzed, and the theoretical model for a dual-FBG sensing structure is established. The two FBGs with different Bragg wavelengths are symmetrically attached onto the surface of the sensing axis, and used as sensing and reference elements, respectively. The structure can effectively relieve the thermal effect and eliminate environmental perturbation. After the calibration of axial torque with respect to Bragg wavelength by using a torque gauge, the measuring range of the fiber-optic torque sensor is 0~15 Nm, the sensitivity is 90.2 pm/Nm, the linearity is 0.9957, the repeatability error is 3.25 %FS, and the hysteresis error is 2.0 %FS. The torque sensing shaft is connected to the driving shaft of a stepper motor with a flexible coupling, and transient torque is obtained in real time with a frequency response bandwidth of <35 kHz, which is limited only by the readout speed of the interrogation system. This work provides a new technique for transient torque measurement of a motor.
Research progress on the application of laser ablation absorption spectroscopy
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Laser ablation absorption spectroscopy (LAAS) is an analytical technique by combining diode laser absorption spectroscopy (DLAS) with laser ablation (LA) technique. It has been developed to atomize various samples and distinguish elements and isotopes directly without chemical separation. This article reviews the principle and recent research highlights of LAAS technique.
Quality evaluation for adaptive optical image through a logarithmic deviation of Rényi entropy
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The adaptive optical telescopes play a more and more important role in astronomy and satellite detection, and the space target images are so many that we need find a suitable method of quality evaluation to choose good quality images automatically in order to study the restorate image. It is well known that the adaptive optical images are no-reference images. In this paper, a new evaluation method based on the use of the logarithmic standard deviation of Rényi Entropy for the adaptive optical images is proposed. Through the discrete cosine transform using one dimension window, the statistical property of Rényi entropy for images is studied. The different directional Rényi entropy maps of an input image containing different information content are obtained. The mean values of different directional Rényi entropy maps are calculated. For image quality evaluation, the different directional Rényi entropy and its standard deviation corresponding to region of interest is selected as an indicator for the anisotropy of the images. In this paper, we define a logarithmic measure the standard deviation based on Rényi entropy can be selected as an indicator of quality evaluation for adaptive optical images. Experimental results show the proposed method that the sorting quality matches well with the visual inspection.
Ultrafast microwave frequency measurement based on electro-optic tunable Fabry-Perot etalon
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In modern radar systems and electronic warfare systems, instantaneous microwave frequency measurement (IFM) is widely used for detecting and roughly classifying unknown signals. However, conventional electrical approaches realizing IFM have hit the bottleneck of limitation in measurement range due to the limited bandwidth of the electronic components. Photonics-based approaches for microwave spectrum analysis are considered to be competitive alternatives because of the advantages such as wide instantaneous bandwidth, low loss and immunity to electromagnetic interference. In the past decades, a few methods of photonic approaches have been proposed. A tunable fiber Fabry-Perot interferometer (FFP)1 and a fiber Bragg grating2 used as an optical scanning receiver were reported, but the response time is long due to the piezoelectric ceramics (PZT) or electric heating driven systems, the scanning speed is only 200 Hz 2. IFM based on frequency-amplitude mapping technique was previously demonstrated.3, 4 However, the measurement range is limited to about 20 GHz and the accuracy varies in the whole range. In recent years, frequency measurement based on stimulated Brillouin scattering (SBS) with high resolution was reported,5, 6 but the existence of a scanning microwave signal source made the system complex and the response time is depended on the sweeping speed of the local oscillator, which is of the order of milliseconds. In Ref. 7, a system integrating SBS and a frequency shifting recirculating delay line (FS-RDL) was demonstrated. The sweeping time is about hundreds of microseconds, but there is a trade-off between sweeping time and measurement range. Measurement period of 5 s in 20 GHz range has been realized by channelized radio frequency measurement scheme.8 However, the implementation of an analog-to-digital converter with bandwidth of 2 GHz made the system complex and costly.
In this work, a novel approach of ultrafast frequency measurement based on electro-optic Fabry-Perot (EOFP) scanning receiver is proposed for the first time. In comparison with other frequency scanning measurement systems, which use methods such as mechanical tuning, electric heating, scanning microwave signal, FS-RDL, etc., our double-EOFP system can measure signals with frequency under 54 GHz in 2 s, which is the fastest scanning rate as far as we know.
Image correction method without gain correction in grating-based x-ray phase-contrast imaging
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Grating-based X-ray phase-contrast imaging (GPCI) provide complementary attenuation, phase, and scattering contrasts simultaneously, especially useful for imaging samples comprising of mostly low atomic number elements (low-Z materials). These powerful imaging abilities have important applications in medical diagnostics and biological research. Critical optical components such as gratings in GPCI make GPCI more sensitive, at the cost of difficulties in the experimental operation. In this study, a new detector image correction method in GPCI is developed to simplify the data collection and image processing. Generally, both offset (dark-current) and gain corrections need to be performed for conventional image correction. Based on the principle of GPCI, here we analyze theoretically the influences of dark-current and inhomogeneity of the detector on the images of GPCI, and find that only the offset correction is necessary for the attenuation and scattering contrast images. Then, a simplified image correction method without gain correction is proposed for GPCI. The experiments performed on a prototype for non-interferometric grating-based X-ray phase-contrast imaging confirm the feasibility and validity of the proposed method. Compared with conventional image correction, the new image correction method can achieve the same performance only with offset correction. Therefore, the new method simplifies the experimental operation and facilitates the use of GPCI for radiographic applications in materials science, biomedical imaging, and industrial non-destructive inspection.
Influence of void inside bonding layer on laser damage threshold of high reflective coating of thin disk laser
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With thin disk laser under intensive pumping high heat flux go through the bonding area with voids inside it will introduce local temperature and stress increase in high-reflective(HR) coating above bonding layer. This will influence the laser damage threshold(LDTH) of local HR coating. An analytical model is developed to analyze the HR coating of thin disk laser illuminated by high fluence pulse laser considering crystal pumping and void inside bonding layer. Analytical results show that the area of HR coating is stressed and heated under crystal pumping. When illuminated by high fluence pulse laser the coating at this area has higher thermal stress. With pump density of 5kW/cm2 if the radius of the void is larger than 100um the LDTH of HR coating will be affected by the void significantly. And the larger the void size is the lower the LDTH of HR coating is. Relative lower laser damage threshold of HR coating above bonding void is testified by experiment.
Preliminary performance test of tubular neutron detector based on SiPM signal readout
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Due to the shortage and the rapidly increasing price of the 3He gas, seeking new types of position-sensitive neutron detectors is urgent. In order to fulfill the requirements of Chinese neutron spectrometers for neutron detectors, the research on neutron detector based on 6LiF/ZnS (Ag) scintillator and wavelength-shifting fiber (WLSF) structure neutron detectors was developed. It has the advantages of high neutron detection efficiency, good position resolution and the ability to splicing large areas. This paper proposed a tubular neutron detector structure. It consists of two layers of rolled 6LiF/ZnS(Ag) scintillators sandwich with two wavelength-shifting fibers, and two SiPMs (Silicon photomultipliers) for the photons readout. By MC simulation, we obtained the thermal neutron conversion efficiency of 6LiF/ZnS(Ag) scintillation screens with different thicknesses and rolled diameters, and optimized the detector structure. The characteristics of the key components are studied. A small detector prototype has been constructed. and been tested by the neutron beam. The preliminary test results showed that the detector can work well.
The neutron scintillator detector arrays (NSDA) for the GPPD in the CSNS
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Chinese Spallation Neutron Source (CSNS) is under construction in Guangdong province since 2008. The investigation of the Neutron Scintillator Detector Arrays (NSDA) have been developed to fulfill the requirements of the General Purpose Power Diffractometer (GPPD). The detector module consists of 6LiF/ZnS (Ag) scintillators, crossed WLSF arrays, multi-anode photo multiplier tubes (MA-PMT), and the ASIC readout electronics. The position resolution of the detector module is 4mm×4mm, and the thermal neutron detect efficiency is better than 45%. 38 detector modules for phase I of the GPPD have been finished and been installed in GPPD in Aug., 2017. Joint debugging with neutron beam in the GPPD was started at the CSNS on November 1, 2017. During the 10-day joint debugging period, the NSDA successfully obtained diffraction data. The instrument resolution of the diffraction data for the standard Si powder for high angle banks is calculated to be 0.184%. It is better than that of the physical design.
Temperature bandwidth in the spatial directions of YCOB
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YCa4O(BO3)3 (YCOB) was found to have a large temperature bandwidth in XZ optical principal plane. By considering the thermal rotation effect, the temperature bandwidth in spatial directions were studied by theoretical derivation and frequency doubling experiments. The temperature bandwidth in maximum effective nonlinear optical coefficient (deff) direction was not as big as that in (30.8°, 180°) direction. The light propagate in the second quadrant was found to have bigger temperature bandwidth than the first quadrant. And the temperature bandwidth was found to change as the wavelength change of fundamental frequency light.
Single crystal silicon: surface evolution regularity of chemical etching and effect of nano jet polishing on damage precursor
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Single crystal silicon is a chemically active semiconductor material with good processing characteristics. With the development of technology, the role of single crystal silicon components in the field of ICF is becoming more and more important. Restricted by traditional processing method and MRF, damage precursors such as scratches and impurities still remain on the surface after processing. That may influence the performance of the elements. In this paper, we study the effect on the surface by two chemical etching methods and the influence on the damage precursors of nano jet polishing. We used HF solution/HNO3 and KOH/ isopropanol to etch the surface of the element. When the etching depth comes to 0.2 μm, pits and scratches could be easily found on the surface. After the etching process, the element was processed by nano jet polishing and the roughness decreased from 1.264nm to 0.986nm.We used nano jet polishing method to process the element polished by MRF in order to research the evolution of comet-tail scratch. The In-situ tracking method was also applied in this study. After the polishing process, the W-D (width to depth ratio) increased from 30.51 to 45.84. The scratch was deactivated and the PTA (photothermal absorption) decreased from 1.5413nA to 1.3500nA. The Ce impurities were also removed. Its concentration decreased from 0.1162mg/L to 0.0005mg/L and the PTA of the element decreased from 0.3044nA to 0.0652nA. From the research, we can easily know that the subsurface damage exposed after the etching process. That may lay the foundation of the nondestructive processing of single crystal silicon. After nano jet polishing process, the quality of the element became better. The roughness and concentration of Ce impurities decreased. The damage precursors were deactivated and the PTA decreased. In a word, chemical etching could expose the surface damage of single crystal silicon and nano jet polishing can improve the laser damage resistance.
Design and fabrication of wide-band LiNbO3 electro-optical modulator
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A Wide-Band LiNbO3 Electro-Optical Modulator was designed and Fabricated. The LiNbO3 integrated optical intensity modulators consist of Mach-Zehnder interferometer optical waveguide circle and coplanar waveguide (CPW) modulation electrode structure. The effects of CPW’s parameter on the transmission performance of microwave by using the finite element method. Experimental results show that the fabricated Modulator obtain insert loss of 3.5dB, the extinction ratio of 30dB, the half-wave voltage of the DC electrode of 4V，the half-wave voltage of the traveling-wave electrode of 5.5V, the power reflection of less than -13dB, the 3dB bandwidth of 18GHz
Research on self-calibration algorithms based on optical fiber distributed sensing technology
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In recent years, distributed optical fiber temperature measurement system has been widely used in industrial safety field. In this paper, the principle of distributed optical fiber temperature measurement system is introduced and the system performance is tested. The design and development of self-calibration system without real-time temperature compensation is carried out. The measurement accuracy of the system is improved. The distributed optical fiber temperature measurement system with low power consumption and high performance has been applied in the goaf and cable temperature field of coal mine, which provides a favorable detection method for the safety detection of coal mine underground.
Simulation of Kolmogorov-like atmospheric turbulence using a high-resolution liquid crystal on silicon device
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Kolmogorov-like atmospheric turbulence is simulated through loading phase screens in sequence onto a liquid crystal on silicon (LCoS) device. Generated phase screens are calculated using power spectrum density method, together with compensation of loss of low frequency by Harmonic method. The computed result of phase structure function shows that after 4 times compensation of Harmonic method, phase screen can simulate Kolmogorov-like atmospheric turbulence accurately. In experiments, a LCoS device manufactured by Holoeye incorporation is calibrated to ensure Precise phase modulation, including inherent wavefront distortion and modulation phase depth. After that, excellent experimental results of dynamic turbulence simulation are demonstrated.
Research on ultraviolet imaging detection of high-speed aircrafts
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Ultraviolet spectroscopy analysis of aircraft plume region is a new breakthrough in high-speed aircrafts detection technology. The main difficulty lies in obtaining spectral information and flow field information of aircraft plume. Firstly, based on the high-temperature radiation of high-temperature alumina particles and the secondary combustion theory of unburned fuel, the flow field of the tail flame is simulated. The simulation chamber adopts a variety of solutions and network convergence methods. The temperature, pressure and gas density distribution of the tail flame field can be obtained by simulating the tail flame flow field. Secondly, the atmospheric channel characteristics of ultraviolet detection are studied in this paper. The calculation of spectral irradiance of the plume target and the earth background ultraviolet radiation reaching the pupil of the camera is very important for the design of the detection system. Combining the absorption and scattering characteristics of the atmosphere to the ultraviolet wave band, the ultraviolet imaging detection scheme for the target tail flame is established. For the research of ultraviolet detection channel, the atmospheric radiation transmission software MODTRAN is selected to carry on the preliminary simulation research. The absorption and scattering of all atmospheric molecules and the absorption and scattering effects of aerosols and clouds are calculated by calculating the path transmittance, atmospheric emissivity, single or multiple scattering of solar and lunar emissivity and direct transmission of solar radiation.
Research on calibration and data processing method of dynamic target monitoring spectrometer
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The addition of potassium salt to the propellant of aircraft can effectively reduce the secondary combustion of the wake flame and the difference between the background radiation, which makes the targets detection more difficult for traditional infrared method. Based on high-spatial-resolution, high-throughput and compact spatial heterodyne spectroscopy(SHS), the dynamic target monitoring spectrometer(DTS)detects the potassium spectral lines of 766.49 nm and 769.90 nm by combining the one-dimensional spatial imaging with the two-dimensional orthogonal detection mode. The spectral range and resolution of the two channels of DTS were calibrated by the hyperspectral monochromatic uniform light source scanning system. The relative response consistency correction and absolute response coefficients of the two channels were calibrated by using the large-aperture integrating sphere, and the target spectral lines were extracted by background difference and target spectral line isolation. The target spatial was located and spectrum synthesis was carried out according to the spectral and radiation calibration results and the corresponding relation of the two-dimensional field of view. Finally, a complete data processing flow of DTS is established. In order to test the DTS developed by the laboratory, the target was simulated by adding K2SO4 to the burning alcohol in the outdoor environment. The detected target was successfully recorded through two-channel spectrum synthesis, showing the dynamic change process under the influence of outdoor wind during the combustion process, which verified the rationality of the processing flow.
Three-dimensional structure analysis of EB-PVD thermal barrier coatings
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The three-dimensional structure of thermal barrier coatings has an important effect on its performance. Thermal barrier coatings prepared by electron beam physical vapor deposition (EB-PVD) was investigated, and a hightemperature oxidation experiment at 1050℃ was carried out, three-dimensional(3D) imaging were performed by micro- CT and focused ion beam-scanning electron microscopy, and the three-dimensional structure of EB-PVD thermal barrier coatings was obtained. Three-dimensional distribution of thermally grown oxide, inter-diffusion zone, pores, microcracks were obtained, and the thickness of TGO and micro-cracks were quantitatively analyzed. The results show that the TGO thickness analyzed by micro-CT and FIB-SEM are consistent with SEM results, the average depth of microcracks is 0.14 μm, and the micro-cracks only can be observed by a higher resolution micro-CT.
Advances in research on optical transmission properties and sensing of magnetic fluids
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The optical transmission properties of magnetic fluids have important theoretical research and application value. Firstly, the optical transmission properties and the influence mechanism of magnetic field on the optical transmission properties of magnetic fluids are introduced. The theoretical method of studying magnetic fluids under magnetic field is introduced. Then the effects of different factors on the optical transmission properties of magnetic fluids and the research progress of sensing applications based on the optical transmission properties of magnetic fluids are reviewed. Finally, the application of the optical transmission properties of magnetic fluids is prospected.
Application of region of interest CT in analysis of CMC plate-like component
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Aiming at the three-dimensional imaging of ceramic matrix composite (CMC) plate-like component, and the higher resolution imaging requirement of the local region of interest (ROI) in practical engineering applications, imaging experiment of CMC plate-like component was performed by the ROI computed tomography(CT), the resolution of CT imaging reached 28.4 microns, and three-dimensional(3D) imaging of the ROI in CMC plate-like component was realized. The characteristics of pores and typical weaving defects were analyzed from the three-dimensional structure, the three-dimensional morphology of internal pores and typical weaving defects were extracted and visualized respectively. The results show that the region of interest CT can meet the requirements of three-dimensional imaging of focus area of CMC plate-like component, and the 3D morphology, fiber weaving, pores and porosity of CMC plate-like component can be characterized, the porosity of ROI is about 13.23%.
Optical power cable and accessory research
Baoyi Yuan,
Hao Zhang,
Ze Yuan,
et al.
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Optical Power Cable is an infrastructure industry that realizes intelligent society and is widely used in electric power, transportation, oilfield, mining, industry, residential and other fields. Optical Power Cable transmits energy and information at the same time, in the same path and in the same direction, and monitors the operation status of lines and equipments, which realizes multiple functions by laying Optical Power Cable at one time, saving material and space resources. Optical Power Cable is composed of an optical unit and an electric unit, and is used for transmitting information and energy, respectively, and real-time and online monitoring by using the optical unit. The paper first reviews the research of Optical Power Cable. Since the invention of Optical Power Cable by Baoyi Yuan in 2006, the Optical Power Cable industry has developed rapidly, forming a series of models and related accessory. Then analyzes the typical structure and composition, Optical Power Cable is mainly composed of two parts, an optical unit and an electric unit, with optical fibers and conductors as main parts, respectively. Finally, introduces the accessory, including the high-voltage Optical Power Cable optical power insulation separator, Optical Power Cable junction box. Optical Power Cable has broad application prospects, and it is widely used in smart grid, energy interconnection, smart city, smart transportation, smart community, smart home and other fields, and has important research and application value. Keywords: Optical Power Cable, energy, information, sensing, optical unit, electric unit.
Information extraction of vibration based on Ф-OTDR vibration sensing system using different signal processing algorithms
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A phase-sensitive optical time-domain reflectometric (Φ-OTDR) system based on the direct detection is demonstrated. It uses amplitude difference and two-dimensional Fourier transform method to extract the vibration information with a frequency response range from 5Hz to 2.5kHz, with a frequency resolution of 1 Hz, and the longest sensing length has reaches 9.8km. Then, a vibration positioning scheme based on hybrid Gaussian model is introduced, which is able to overcome the system error caused by laser power drift and successfully reduce the positioning error in the vibration-free region. A Φ-OTDR system based on the heterodyne detection is also proposed. Using self-mixing as demodulation method and the bilateral filtering algorithm in image processing as signal filtering method, this system preserves the information of vibration while filtering the background noise and improves the signal to noise ratio. Compared with the positioning result under direct detection scheme, there is a great improvement of result under this heterodyne detection scheme, and a better frequency response as low as 3 Hz is obtained.
Channel analysis of free-space quantum key distribution with untrusted node
Wei Li,
Yu Li,
LinLin Jin,
et al.
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Various optical quantum key distribution protocols have been proposed and examined to implement a global quantum communication system both in fiber-based network and in free-space systems. Employing a satellite as a quantum relay is a possible solution to increase the secure covered distance, which is available for sharing secure keys between two remote ground stations. In this paper, combining with the idea of measurement device independent quantum key distribution, a modified free-space quantum communication protocol is proposed to build a QKD network with untrusted nodes, where the parties on the ground send quantum signals to the untrusted satellite relay that perform a joint measurement on the incoming signals. Our results demonstrate that though the modified protocol suffers higher link attentuation than the entanglement-based quantum communication protocol owing to higher effects of atmospheric turbulence for uplink, our modified protocol provides secure quantum communications with untrusted relays. Furthermore, the complex and non-space-qualified sources remain on the ground in our scheme , which makes our scheme more practical for bridging a seamless connection form ground to space.
Research on magnetorheological finishing of aspheric optics for single-crystal silicon
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Single-crystal silicon is a typical infrared optical material, commonly machined by single-point diamond turning (SPDT) with micro-level figure accuracy and nano-level roughness. However, the tool marks, surface damage and middle-frequency error left by the diamond turning process may greatly affect the imaging quality. Magnetorheological finishing (MRF) is a deterministic, sub-aperture polishing technology that is very helpful in improving both surface nano-roughness and surface figure and can be used to polish silicon materials. Although the feasibility of MRF for single-crystal silicon has been proved, there are still some problems such as low material removal rate and uncontrollable surface integrity. In this study, the MRF mechanism for single-crystal silicon was explored, and the preparation method of MR fluid was optimised. An experiment was performed to machine a large-aperture single-crystal silicon aspheric surface on an MRF machine developed by China Academy of Engineering Physics. After polishing for several times, the figure accuracy PV improved from 5.9 μm to 0.56 μm, and roughness Rq reduced to 1.2 nm, verifying the excellent performance of MRF in infrared material processing.
Study on correction method of radiative heat flux measurement of flame tube wall
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The measurement of radiant heat flux in flame tube is usually non-contact, so various factors should be considered in the actual measurement process. In order to improve the accuracy of measuring radiant heat flux on the inner wall of the flame tube, a flame tube model was used as the research object in this paper. A high temperature gas radiant heat flux wind tunnel measurement system was established to measure the wall radiant heat flux under different combustion conditions. The results of the test and numerical simulation were compared, and the relative error between the revised test and numerical simulation results was kept between -38.89% and 32.54%.
In-flight real-time altitude-independent magnetometer-bias determination for micro-satellite
Zhen Zhang,
Jianping Xiong,
Cheng Ma
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In this paper a new real-time algorithm is proposed for in-flight magnetometer bias determination without altitude knowledge for a micro-satellite. This approach introduces iterative algorithm to the traditional statistical calculation and extends the batch method to satisfy real-time application. It makes the estimation of magnetometer bias simple using iterative calculation instead of large-scale matrix computation. Experiment results indicate that the new real-time algorithm is more accurate and faster compared with other algorithms, even with real noise data. With the new real-time algorithm, a magnetometer calibration can be taken on-orbit and will reduce the demand of computing power.
New fabrication method of step plate for measuring instrument transfer function of interferometer
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Phase step plate has the property of step function, and it can be used to measure the interferometer system transfer function (ITF), which is used to objectively evaluate interferometer spatial frequency response characteristics. The traditional fabrication method of step plate is lithographic exposure combined with reactive ion beam etching method, which is costive, and not suitable for fabricating large diameter step plate. In this paper, a new fabrication method of step plate based on blade-mask coating technology is proposed. A step plate of 100mm diameter and 103.5nm step height is successfully fabricated, and the surface roughness, homogeneity, steepness of the step plate are satisfied for measurement requirements. Furthermore, the coated step plate is used to measure the ITF compared with an etched step plate, and the measurement results of two plates differ by no more than 5%, which shows a good consistency. Thus, the reliability of coated step plate for ITF measurements is proved.