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- Frontiers in Optical Imaging Technology and Application
- THz Technology and Application
- Front Matter: Volume 9795
Frontiers in Optical Imaging Technology and Application
Study on the technology of mutual alignment based on the four-quadrant photo electric detector
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Panoramic stereo cameras and laser radars have their own coordinate system in the dynamic spatial sensing area and they have to determine the position relationship between each other through joint calibration. As using the traditional technology of mutual alignment based on the telescope cross wire is tedious and requires high operating skills, a new method of mutual alignment using lasers and four-quadrant photo electric detectors is provided after analyzing the working principle of four-quadrant photo electric detectors. Firstly make the laser beam irradiate the active area of the four-quadrant photo electric detector through coarse aiming. Then the center of a light spot offset relative to the center of the active area can be obtained according to the output voltage of four quadrants. The pose of two instruments can be adjusted properly to realize mutual alignment. The experimental results indicate that the alignment accuracy of four-quadrant detectors can meet the requirements of mutual alignment, which provides a new idea for joint calibration.
Pupil-resizing Fourier ptychography
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We present a coherent approach of complex amplitude reconstruction, termed aperture-resizing Fourier ptychography (FP). The reported approach resizes the pupil size of an imaging system and captures the corresponding intensity images. The acquired images are then synthesized in the frequency domain via iteration computation to reconstruct a complex sample wavefront without known phase information and interferential optics. Like holography, it is capable of reconstructing all information of the object. The reported aperture-resizing FP may find wide applications in 3D refocusing, 3D object tracking, remote sensing and microscopy.
A calibration algorithm for the voltage-phase characteristic of a liquid crystal optical phased array
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Liquid crystal optical phased array (LCOPA) is a kind of spatial light modulator(SLM) which is now widely studied in the field of laser radar, adaptive optics, optical information processing, etc. The calibration of the voltage-phase characteristic of a LCOPA is an important step which will seriously affect the performance of a LCOPA. Firstly, derived the relationship between the phase distribution of the emergent light and light intensity in the far-field. Designed an optic path to calibrate the voltage-phase characteristic. And built up a observation equation. Introduced a weight matrix to reduce the errors caused by the impact of phenomena such as the fly-back. Proposed a new calibration algorithm based on the measurement of light intensity. A checkerboard pattern with a period of M pixels per check was used in the calibration routine. Fix the control voltage of one region, and change the voltage in another region. The light pattern in the far-field changes with the control voltage. Measure the intensity of the light beam at the center of the far-field. Then, obtain the raw data. Filter and normalize the raw data. And calculate the phase difference between two regions. Use weighted least square method to get the relationship between the control voltage and the phase retardation. Lastly, using this method to calibrate a LCOPA which is produced by BNS corp.
Athermalization design of collimating lens system for space solar telescope
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The Solar Magnetic Field Telescope (MFT) , which imaged directly towards the sun , received about 1000W heat load irradiating into the telescope system, resulting in changes of ambient temperature. According to the principles of athermal design, a collimating lens system was designed, allowing MFT to work properly between a wider temperature range . The collimating lens system with F number of 3.55, worked in the visible spectrum, had the effective focal length of 156.4mm and the full field of view of 2.8 arc min ×2.8 arc min. Through the passive optical athermal method , the optimized lens works at ambient temperature ranging from -40℃ to 60℃.The radii of RMS are all smaller than the pixel pitch. The image quality approaches to diffraction limit and the MTF value is over 0.75, which satisfies the system specifications.
Calibration method of focal plane for static multi-star simulator
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The calibration work was important to the development of star sensor, improving the accuracy of star simulator was very important for the calibration of star sensor. In reality, being limited in manufacturing technology, assembling and testing facility and so on, it was very difficult to achieve the precision of design theory, especially the star angular distance. In this paper, from the accuracy of angular distance of star simulator, combined with the installation practice, through real-time monitoring of theodolite, and put forward a quantitative method of focusing. Experimentation have shown that the method can realize the accurately focusing of star simulator, all the angle distance error finally were less than 7.72″, and can improve the installation efficiency.
Numerical simulations on polarized photon scattering for classification of air pollutants
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Atmospheric pollution has become a key factor restricting the development of social economy. Identification of major pollutants has important scientific significance. The polarization evolution during polarized light interacting with particulate matters can provide important information sensitive to properties of particles. We propose a method to recognize the specific component in air dust, for example, the sand. Based on our polarization simulation, we show theoretically that some Stokes parameters at specific scattering angle can classify water soluble particles, water droplet and sand etc. The preliminary research implies some potential of polarization detection applied in source apportionment for air pollution monitoring.
A light properties’ quantification algorithm based on illumination and singular points
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In this paper an algorithm based on light radiation model and combined with the singularities of gradient descent and strengthening method to describe the light sources is presented, which gives a way to describe light sources. The entire model does not need any limitations for the light sources, which greatly enhanced the applicability of this model. The results show that it shows a great potential on the problem of quantifications for light sources and tracking. We think that this method would present a way that helps us to research in a different way and describe illuminant not only based on physical quantities, but also on the feature in the image. A light source tracking method is under experiment.
Large aperture diffractive telescope design for space-based lidar receivers
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Diffractive telescopes are ideal to space-based lidar receivers, because of their advantages of mass and surface shape tolerances. To develop diffractive optical systems, the aberration properties and high order diffraction of diffractive lenses were discussed. The aberration properties are suitable for lidar receivers. High order diffraction is helpful to improve diffractive lens fabrication and decrease system length. And it can be realized by modifying the surface figures of a diffractive lens, mainly the ring widths and depth. A 1-meter aperture diffractive telescope design with simple structure was given, providing spot diameters less than 45μm over the whole field of view.
Infrared polarization image texture extraction via variational decomposition algorithm
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As to extract better texture from an infrared polarization image, variational decomposition has a good effect which extracts texture in the premise of energy index. First this paper introduces description of infrared polarization image in Stokes vector and hierarchical variational decomposition (BV, Gp, L2) model. And we use this model method for multiscale texture extraction of the infrared polarization image. A given infrared polarization image is decomposed into the characteristics of the three different components of u, v, r through the minimization of the energy functional. In this decomposition, v represents the fixed scale texture of f , which is measured by the parameter λ. To achieve a multiscale representation, we proceed to capture essential textures of f which have been absorbed by the residuals. Then we make energy as an index of the texture evaluation. The experiments show that the algorithm is effective to extract better texture from an infrared polarization image.
The algorithm of image fusion for infrared polarization based on Contourlet transform and Teager operator
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This paper puts forward a infrared polarization image fusion algorithm by using Contourlet transform and 2-D Teager operator. First of all, based on Contourlet transform , infrared polarization image has been decomposed into low frequency and high frequency . Using Teager operator to process the high frequency sub-bands, and then select by different regional characteristics based on maximum contrast ratio. As for the low frequency sub-bands, judged by energy, selects the weighted weights to fuse the image . At last, we get the experimental results and our analysis. The results of the experiment show that compared with the traditional, the algorithm in this paper can give better characterization of polarization remote sensing image edge and texture information, has a higher resolution, and also improves the visual effect of the polarized remote sensing image.
Feedback circuit design of an auto-gating power supply for low-light-level image intensifier
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This paper introduces the basic principle of auto-gating power supply which using a hybrid automatic brightness control scheme. By the analysis of current as image intensifier to special requirements of auto-gating power supply, a feedback circuit of the auto-gating power supply is analyzed. Find out the reason of the screen flash after the auto-gating power supply assembled image intensifier. This paper designed a feedback circuit which can shorten the response time of auto-gating power supply and improve screen slight flicker phenomenon which the human eye can distinguish under the high intensity of illumination.
A portable swappable method scientific CMOS image data storage system
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In the field of deep space exploration, the detector needs high-speed data real-time transmission and large capacity storage. SATA(Serial advanced technology attachment) as a new generation of interface protocols, SATA interface hard disk has the advantages of with large storage capacity, high transmission rate, the cheap price, data is not lost when power supply drop, so it is suitable for used in high speed large capacity data storage system. This paper by using Kintex-7 XCE7K325T XILINK series FPGA, the data of scientific CMOS CIS2521F through the SATA controller is stored in the hard disk. If the hard disk storage is full, it will automatically switch to the next hard disk.
Vehicle-mounted real-time digital voice communication system based on visible light communication
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Based on the phenomenon that more and more cars use LED for lighting and the current rise of visible light communication technology, this paper proposes a vehicle real-time voice communication system with high reliability on the basis of visible light communication for verification. The paper introduces the design of digital audio collection and output module, On-Off Keying (OOK) modulation and demodulation, Reed-Solomon encoding and decoding module, array LEDs emission and the module of PIN receiving signals. The LED lamp frequency response, communication distance, error rate and other parameters are tested and calibrated. The digital audio real-time communication system’s receiving speed is 500Kbps when the communication distance is 3.9 meters.
Airborne laser communication technology and flight test
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Reconnaissance aircraft is an important node of the space-air-ground integrated information network, on which equipped with a large number of high-resolution surveillance equipment, and need high speed communications equipment to transmit detected information in real time. Currently RF communication methods cannot meet the needs of communication bandwidth. Wireless laser communication has outstanding advantages high speed, high capacity, security, etc., is an important means to solve the high-speed information transmission of airborne platforms. In this paper, detailed analysis of how the system works, the system components, work processes, link power and the key technologies of airborne laser communication were discussed. On this basis, a prototype airborne laser communications was developed, and high-speed, long-distance communications tests were carried out between the two fixed-wing aircraft, and the airborne precision aiming, atmospheric laser communication impacts on laser communication were tested. The experiments ultimately realize that, the communication distance is 144km, the communication rate is 2.5Gbps. The Airborne laser communication experiments provide technical basis for the application of the conversion equipment.
The index analysis and structure selection of LEO space laser communication terminal
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In order to achieve low orbit optical compartment for three generations of high-speed laser communication links which between geostationary relay satellite, It had to be designed to meet the use of laser communication terminal background paper for this with the background and the optical compartment specific installation location of the remote machine indicators such as the range of rotation, can pass the time, coarse tracking accuracy, the fundamental frequency, rotational speed, acceleration and weight were analyzed. Obtain azimuth rotation range of ± 135 °, pitching rotation range of ± 60 °, 24h passing time 50525.912s, coarse tracking accuracy 49.4 μrad other indicators, and the typical space laser communication terminal structure were analyzed according to indicators and program aims to analyze the advantages and disadvantages of the requirements proposed structure for this project, tracking frame structure is based on the optical path of the KUDE Cross.
Airborne space laser communication system and experiments
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Airborne space laser communication is characterized by its high speed, anti-electromagnetic interference, security, easy to assign. It has broad application in the areas of integrated space-ground communication networking, military communication, anti-electromagnetic communication. This paper introduce the component and APT system of the airborne laser communication system design by Changchun university of science and technology base on characteristic of airborne laser communication and Y12 plan, especially introduce the high communication speed and long distance communication experiment of the system that among two Y12 plans. In the experiment got the aim that the max communication distance 144Km, error ＜10-6（2.5Gbps） ＜10-7（1.5Gbps），capture probability ＞97%, average capture time 20s. The experiment proving the adaptability of the APT and the high speed long distance communication.
Imaging simulation and analysis for spot targets in space based optical sensors
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In space based optical surveillance systems, the targets could be points, spots or special shape, it depends on the sensors’ parameters. This paper proposed a method to divide the target’s surface into infinitesimal according to a simplified model, then the ray tracing method is used. Typical effects resulting from sensors’ parameters are considered. Imaging simulation results indicates that target’s plume flow images produced by this method are logical and can be applied to validate data processing algorithms.
Inter-satellite laser link simulation analysis
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The characteristic of satellite communication link was firstly described and four application modes were put forward. By comparison, it is suggested that microwave link is used in satellite-to-ground communication and laser link is used in inter-satellite communication. Secondly the condition and composition of laser link establishment was analyzed and laser link model was set up, and the principle and composition of APT system was described. Finally, based on STK and MATLAB platform, the process of inter-satellite laser link establishment was designed, and setting the scene of TDRS capturing and tracking user’s satellite as an example, simulation was realized and demonstrated.
Ultraviolet irradiance calibration system based on standard detector
Facai Zhao,
Quanshe Sun,
Shaoshui Wang,
et al.
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We present a special facility for accurate calibration of instrument’s irradiance responsivity in ultraviolet spectral region to overcome the troubles caused by the weak ultraviolet response of most spectral radiometer and poor signal-to-noise ratio. In this system, a Seya-Namioka monochromator with a small f-number is designed to get more energy as an irradiance source. Reference standard irradiance detectors, calibrated against to primary standard detector traceable to cryogenic radiometer for spectral power responsivity, are used to determine the irradiance at a reference plane. The typical combined standard uncertainties in irradiance responsivity calibrations using this system can be 2.3%.
Study of the laser induced acoustic under water source aim at imaging and detecting
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This paper addresses itself to the problem of interaction mechanism of laser induced acoustic source under water. The main photo-acoustic mechanisms include thermal expansion, vaporization and optical breakdown as well as the photon beam pressure. We integrate these into a compound model and compare numerical calculation and simulation results with the existing experimental data. The different energy density thresholds between different mechanisms are calculated. We optimize original thermal expansion by considering various laser pulse-shapes especially Gaussian laser. When discussing vaporization, random bubbles distribution is studied instead of single bubble alone for the first time. Detection distance, pulse duration, laser energy and spot size in heating area all have effect on sound filed intensity, which are studied through this paper.
Integrated condition monitoring of space information network
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In order to solve the integrated condition monitoring problem in space information network, there are three works finished including analyzing the characteristics of tasks process and system health monitoring, adopting the automata modeling method, and respectively establishing the models for state inference and state determination. The state inference model is a logic automaton and is gotten by concluding engineering experiences. The state determination model is a double-layer automaton, the lower automaton is responsible for parameter judge and the upper automaton is responsible for state diagnosis. At last, the system state monitoring algorithm has been proposed, which realizes the integrated condition monitoring for task process and system health, and can avoid the false alarm.
3D reconstruction of rotational video microscope based on patches
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Due to the small field of view and shallow depth of field, the microscope could only capture 2D images of the object. In order to observe the three-dimensional structure of the micro object, a microscopy images reconstruction algorithm based on an improved patch-based multi-view stereo (PMVS) algorithm is proposed. The new algorithm improves PMVS from two aspects: first, increasing the propagation directions, second, on the basis of the expansion, different expansion radius and times are set by the angle between the normal vector of the seed patch and the direction vector of the line passing through the seed patch center and the camera center. Compared with PMVS, the number of 3D points made by the new algorithm is three times as much as PMVS. And the holes in the vertical side are also eliminated.
Research on the timing sequence control in large laser facility
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The timing sequence, between different pulses in SG-III laser facility, is controlled with three arbitrary waveform generators. The external clock and trigger are used to inhibit the timing jitter, which is provided by the synchronization system. Close-loop monitoring is used to make sure that the temporal phase can be recovered after reboot of the arbitrary waveform generator. The verification experiment shows that the three arbitrary waveform generators can work synchronously , which ensures the synchronization error control of the SG-III laser facility.
Investigation of W-band dielectric constant of coals by free space method
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The dielectric constant of Shandong anthracite coals of China was studied in the frequency range of 75~110 GHz (W-band), using the free space method for the first time. The measurement system is based on the Vector Network Analyzer of Agilent Technology and a VDI extension module with frequency range from 75 GHz to 110GHz. The dielectric constants of coals were calculated from the scattering parameters by implementing an algorithm. Correctness of the test results is verified by measuring the dielectric constant of air and timber. The dielectric constant of each selected coal with different moisture contents is investigated. It is found that both the real and imaginary parts of selected coals exhibit an apparent increasing trend with increasing water content of coals. The real part of coals with different water content varies from 2.61 to 4.97, and the imaginary part from 0.06 to 0.41 at the frequency of 110 GHz. We also obtained the diversification of the dielectric constant by increasing the frequency at the W-band. The real part of coals with different frequency varies from 3.85 to 3.91, and the imaginary part from 0.32 to 0.37 at W-band.
Improved high order grating method to realize wide angle beam steering on liquid crystal optical phased array
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To achieve a wider scanning range of liquid crystal optical phased array (LC-OPA), in this paper, a novel method of improved high order grating (i-HOG) is proposed in one device without introducing any other devices. The method of i-HOG breaks through the traditional ideas of modulo 𝟐𝛑 phase and takes the fringe effect into account to have a multi order extension. Subsequently, the method is verified by numerical simulation showing that it realizes a scanning range of wider than 20 degrees and even wider.
Study of carrier lifetime of silicon by OPTP method
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To analyze the carrier lifetime of Si, a 0.4 mm thickness high-resistivity silicon had been investigated by the optical-pump-terahertz-probe (OPTP) system. The terahertz time domain curve and frequency spectrum (bandwidth of > 6THz) of Si are achieved by the time domain spectroscopy mode, and its characteristic parameters, including refractive index and absorption coefficient, were obtained. And the carrier lifetime of Si was measured by the OPTP mode, the result is about 905 ps.
An integrated membrane sub-harmonic Schottky diode mixers at 340GHz
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This paper presents a sub-harmonic mixer operating over the spectral band 332-348 GHz. The mixers employ integrated GaAs membrane Schottky diode technology. The simulated results show that the conversion loss of the mixer is below dB in the band from 333 GHz to 347 GHz with a local oscillator power requirement of 5mW.The minimum is 8.2dB at 344GHz.
Compressive optical remote sensing via fractal classification
Quan-sen Sun,
Ji-xin Liu
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High resolution and large field of view are two major development trends in optical remote sensing imaging. But these trends will cause the difficult problem of mass data processing and remote sensor design under the limitation of conventional sampling method. Therefore, we will propose a novel optical remote sensing imaging method based on compressed sensing theory and fractal feature extraction in this study. We could utilize the result of fractal classification to realize the selectable partitioned image recovery with undersampling measurement. The two experiments illustrate the availability and feasibility of this new method.
Research on the breakdown mechanism of photoconductive antenna
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Terahertz (Thz) photoconductive antenna is one of the most common devices for the generation of terahertz wave. Basing on the theory of current instantaneous impact model, the most effective way of improving the THZ wave power is to increase bias voltage and laser power, but the damage and the breakdown of photoconductive antenna is easy to occur when the bias voltage increases. In this paper, the physical breakdown mechanism of the antenna is researched on the different trigger positions and the different bias voltages. Trigger position is more likely to be breakdown because of the local high electric field stimulated by photon-generated carriers. Increasing bias voltage not only caused the current increasing quickly, but also ablated thermal breakdown of antenna electrode and resulted in antenna failure.
A terahertz confocal microscope for far-field thermal radiation detection and near-field sub-wavelength imaging
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We present a novel scattering-type scanning near-field optical microscope (s-SNOM) operating in the terahertz (THz) wavelength. A home-made ultra-high sensitive detector named charge sensitive infrared phototransistor (CSIP, detection wavelength ~15 μm) is equipped for spontaneous thermal radiation detection (external illumination should be avoided). Thermal emission from room-temperature objects is collected by a cassegrain objective lens placed above the sample, and focused to a pinhole (d=250 μm) which is kept in liquid-helium (LHe) temperature(4.2 K). With the background radiation from environment efficiently blocked by the low-temperature pinhole, the detector is only sensitive to the THz radiation from a small spot (~λ) on sample surface (the confocal point). As a result, thermal radiation spontaneously emitted by object itself is measured with an excellent spatial resolution of ~14 μm (diffraction-limit). For overcoming the diffraction limit by detecting the near-field evanescent waves, this THz microscope is combined with a home-built atomic-force microscope (AFM). With sharp AFM tip (<100 nm) scattering the evanescent waves with an improved tip-modulation method, we successfully obtained thermal near-field images with a spatial resolution of ~100 nm, which is already less than 1% of the detection wavelength (15 μm). This THz s-SNOM should be a powerful tool for various material research down to the nanometer scale.
Accurate correction of eccentricity errors during microsphere interferometry
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Interferometry is one of the most suitable method for microsphere profile inspection, and the eccentricity errors during measurement is always allowed to exit and corrected by Zernike polynomials fitting method for better dynamic response ability and higher efficiency. The common usage of coordinates on CCD instead of these on wave-front in fitting process may lead to factors errors when effective aperture is bigger than 0.25. In order to correct the eccentricity errors during microsphere interferometry precisely, the impact of normalized polar radius approximating on Zernike polynomials fitting is analyzed. An accurate correction method based on coordinates transformation is proposed, and the calibration method of NA is also given, which will be necessary in the transformation. The experiment results indicate that the PV and RMS value of corrected profile data are 0.1628λ and 0.0326λ separately, and is much more similar to the standard data where the microsphere is placed at the zero-fringe position with the PV and RMS value of 0.1636λ and 0.0332λ separately. So, it can be seen that the correction method is feasible and effective.
Optical tomography in the application of the surface feature extraction
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This paper put forwards a new optical tomographic imaging system, which consists of the rotating periscope system and modulating plate with 65 slits. One-dimensional signals which are divided by modulating plate through the rotating periscope system are collected by photon detector. The paper analyzes the principle of filter back projection (FBP), and chooses the filter that fits the system. It verifies the feasibility of this system by the actual simulation. Choose the circular hole and the calibration image as the target image in scanning experiment, in result of finding that the feature of reconstruction result is obvious, but information of edges is fade. This system plays an important role in developing feature extraction of surface.
Ultrahigh precise and sensitive measurement of optical rotation based on photo-elastic modulation
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A novel technique for improving measurement sensitivity of optical rotation based on photo-elastic modulation is presented. The probe laser orderly passes through a polarizer, the sample to be measured, a photo-elastic modulator(PEM), and an analyzer to be detected. Using the least optical elements to avoid the measurement error may introduced by the other optical elements in the detection light path; other than a reference light path is brought in the measurement system, and differential balance detection method is employed to obtain the AC and DC signal, the common mode noise of light source is efficiently eliminated, then the AC signal is preamplified, and output by a lock-in amplifier, the measurement sensitivity of optical rotation is enhanced further. For our verification experiment, the results show that the precision is up to 0.4％, and the sensitivity is up to 3.17×10−7 rad . So our scheme realizes more accurate and sensitive measurement of optical rotation than any one reported previously.
A discussion of the effect of Spectral Band Width (SBW) on optical glass filter indication
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In order to keep the accuracy of scientific research and experiment results, the primary concern is the accuracy of measuring apparatus. A common way to check equipments is to detect the technical parameters (like transmittance or wavelength indicator) using optical glass filter (already with fixed value). But the applicability and variability of filter are mostly ignored during the process. Improper method will cause false checking result, then brings inaccuracy to research and experiment results. This article will analyze and explicate the using conditions and the applicability of optical glass filter for different equipments. Ways to analyzing the reliability of checking result will also be illustrated through examples.
Optical tweezers and surface plasmon resonance combination system based on the high numerical aperture lens
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Biology and medicine sample measurement takes an important role in the microscopic optical technology. Optical tweezer has the advantage of accurate capture and non-pollution of the sample. The SPR(surface plasmon resonance) sensor has so many advantages include high sensitivity, fast measurement, less consumption of sample and label-free detection of biological sample that the SPR sensing technique has been used for surface topography, analysis of biochemical and immune, drug screening and environmental monitoring. If they combine, they will play an important role in the biological, chemical and other subjects. The system we propose use the multi-axis cage system, by using the methods of reflection and transmiss ion to improve the space utilization. The SPR system and optical tweezer were builtup and combined in one system. The cage of multi-axis system gives full play to its accuracy, simplicity and flexibility. The size of the system is 20 * 15 * 40 cm3 and thus the sample can be replaced to switch between the optical tweezers system and the SPR system in the small space. It means that we get the refractive index of the sample and control the particle in the same system. In order to control the revolving stage, get the picture and achieve the data stored automatically, we write a LabVIEW procedure. Then according to the data from the back focal plane calculate the refractive index of the sample. By changing the slide we can trap the particle as optical tweezer, which makes us measurement and trap the sample at the same time.
Improving transverse resolution of confocal microscopy through spatiotemporal modulation
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A new method is proposed in this paper to improve transverse resolution of a confocal microscope. By setting up the model of a confocal microscope system through spatiotemporal modulation with moving gratings or acousto-optical modulation without defocus distance under coherent light illumination and deducing two-dimensional coherent image formula and transfer function, simulation tests are run with or without spatiotemporal modulation to prove the effectiveness of the proposed method. Simulation results indicate the proposed method can be used to improve the transverse resolution of a confocal microscope system.
T-SDN architecture for space and ground integrated optical transport network
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Integrated optical transport network is the development trend of the future space information backbone network. The space and ground integrated optical transport network(SGIOTN) may contain a variety of equipment and systems. Changing the network or meeting some innovation missions in the network will be an expensive implement. Software Defined Network(SDN) provides a good solution to flexibly adding process logic, timely control states and resources of the whole network, as well as shielding the differences of heterogeneous equipment and so on. According to the characteristics of SGIOTN, we propose an transport SDN architecture for it, with hierarchical control plane and data plane composed of packet networks and optical transport networks.
Calibration for single multi-mode fiber digital scanning microscopy imaging system
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Single multimode fiber (MMF) digital scanning imaging system is a development tendency of modern endoscope. We concentrate on the calibration method of the imaging system. Calibration method comprises two processes, forming scanning focused spots and calibrating the couple factors varied with positions. Adaptive parallel coordinate algorithm (APC) is adopted to form the focused spots at the multimode fiber (MMF) output. Compare with other algorithm, APC contains many merits, i.e. rapid speed, small amount calculations and no iterations. The ratio of the optics power captured by MMF to the intensity of the focused spots is called couple factor. We setup the calibration experimental system to form the scanning focused spots and calculate the couple factors for different object positions. The experimental result the couple factor is higher in the center than the edge.
Multimode nondestructive detecting method for high-speed rail defects
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It is very important to detect the surface defects of the high-speed rail for security concerns. A multimode detecting method, which integrates high resolution of optical image, high precision of photoacoustic detection and strong penetration of ultrasound detecting, is proposed for the rail defect detection. Utilizing the surface defect characteristics obtained from optical signal, the photoacoustic and ultrasound scanning region could be determined, and rail shallow and internal defect characteristics can be acquired subsequently. Eventually, fusing three modal signals mentioned above, the information of the entire rail defect, including type, extension trend and depth can be detected. It has been proved that the multimode method can improve the detecting efficiency, and enlarge the detection range in the meantime.
Control and measuring system of a two-dimensional scanning nanopositioning stage based on LabVIEW
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A control and measuring system of two-dimensional nanopositioning stage is designed for the multiple selection and combinations control based on LabVIEW. The signal generator of the system can not only generate the commonly used control signals such as sine, square, triangle and sawtooth waves, but also generate special signals such as trapezoidal wave and step wave with DAQ data acquisition card. The step wave can be triggered by the other signals for the strict timing corresponding relation between X-Y control signals. Finally, the performance of the control system of two-dimensional nanopositioning stage is conducted by the heterodyne interferometer. The results show that the operation of the system is stable and reliable and the noise peak - valley value is superior to 2nm while the stage moving with 6nm step. The system can apply to the field requiring the precise control to the positioning stage in nano-measurement and metrology.
The application of UV multispectral technology in extract trace evdidence
Jingjing Guo,
Xiaojing Xu,
Zhihui Li,
et al.
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Multispectral imaging is becoming more and more important in the field of examination of material evidence, especially the ultraviolet spectral imaging. Fingerprints development, questioned document detection, trace evidence examination-all can used of it. This paper introduce a UV multispectral equipment which was developed by BITU & IFSC, it can extract trace evidence-extract fingerprints. The result showed that this technology can develop latent sweat-sebum mixed fingerprint on photo and ID card，blood fingerprint on steel hold. We used the UV spectrum data analysis system to make the UV spectral image clear to identify and analyse.
Nondestructive inspection for internal defects of rail based on photoacoustic elastography
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Laser ultrasonic technique is used for the nondestructive testing technology of surface damage, but ignores the density variation in the sample. Photoacoustic elastography is adopted to obtain more rail information (such as the internal defects, the variation of sample’s interior density) of the sample by collecting Rayleigh wave on rail surface and shear wave within the rail. In this paper, it is proved that the internal defects and the variation of density can be detected by photoacoustic elastography, using finite element analysis (FEA). We first use FEA to simulate the ultrasound excitation on the steel material surface excited by the laser source. Two cases of sample are modeled and analyzed, one is with defects of different depth and the other is with different density. Then, an isotropic model using ANSYS is employed and shear wave propagation is modeled. The preliminary results successfully recapitulate the trend of the change of shear wave’s velocities, which shows that the defects can enhance the amplitude of shear wave. In addition, the velocities of shear wave would increase when the density of the sample enlarges. Results from computer simulations demonstrate the effectiveness of photoacoustic elastography with application to quantitative analysis for the structures of sample.
Rayleigh-backscattering doppler broadening correction for differential absorption lidar
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The spectral broadening by Rayleigh backscattering can cause large changes in water vapor echo signals, causing errors when the water vapor concentration is inversed by differential absorption lidar (DIAL). A correction algorithm is proposed to revise the errors due to the effect of laser spectral broadening. The relative errors of water vapor are calculated in cases of different aerosol distribution and temperature changes before and after correction. The results show that measurement errors due to the Doppler broadening are more than 5% before correction and a 2% measurement error after corrected for the case of a smooth, background aerosol distribution. However, due to the high aerosol gradients and strong temperature inversion, errors can be up to 40% and 10% with no corrections for this effect, respectively. The relative errors can reduce to less than 2% after correction. Hence, the correction algorithm for Rayleigh Doppler broadening can improve detection accuracy in H2O DIAL measurements especially when it is applied to high aerosol concentration or strong temperature inversion.
A multi-scale registration of urban aerial image with airborne lidar data
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This paper presented a multi-scale progressive registration method of airborne LiDAR data with aerial image. The cores of the proposed method lie in the coarse registration with road networks and the fine registration method using regularized building corners. During the two-stage registration, the exterior orientation parameters (EOP) are continually refined. By validation of the actual flight data of Dunhuang, the experimental result shows that the proposed method can obtain accurate results with low-precision initial EOP, also improve the automatic degree of registration.
The method of cloud statistics measured with digital holographic imaging system
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Due to the structure of clouds has so many complicated factors, the cloud seeding area is difficult to accurately determined. How to accurately understand the structures of the particle parameters has great significance for weather modification. Digital holographic technology is widely used in particle measurement, because it can realize the three-dimensional particle field measurement and get detail parameters. This paper, based on the research of the holographic reconstruction and image processing algorithm, calculate the equivalent diameter of particle, and obtain the distribution of the particles, for the estimation of the population parameter of particle is put forward a feasible method.
Primary mirror back surface shape research of GEO laser communication system
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The research of laser communication system primary mirror deformation caused by back surface shape variation was done in this paper. The usual mirror back surface shapes were sphere, double arch, flat and biconcave shape and so on. Based on the four shape mirror, with the center hole rim support pattern, the four shape mirror temperature distribution equation was inferred by thermal elastic theory, deformation are compared in 1-5℃ radius direction temperature difference, in the case of minor weight gap and equal maximum thickness. As a result, the deformation of sphere back surface shape mirror is minimal. So sphere back surface shape is fit for the primary mirror.
Can wavefront coding infrared imaging system achieve decoded images approximating to in-focus infrared images?
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Artefacts and noise degrade the decoded image of a wavefront coding infrared imaging system, which usually results in the decoded image being inferior to the in-focus infrared image of a conventional infrared imaging system. The previous letter showed that the decoded image fell behind the in-focus infrared image. For comparison, a bar target experiment at temperature of ﹢20°C and two groups of outdoor experiments at temperatures of ﹢28°C and ﹢70°C are respectively conducted. Experimental results prove that a wavefront coding infrared imaging system can achieve the decoded image being approximating to its corresponding in-focus infrared image.
Compact spectrometer based on concave grating
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In this paper, the compact spectrometer has been designed and implemented with concave grating. By using the holographic corrected concave grating, the compact spectrometer without movable parts, with a fixed grating and an array detector, could obtain a relative high spectral resolution in a wide spectral range. Then, the spectral resolution has been estimated by the slit function. The spectral resolution (ΔFWHM) is smaller than 5nm from 300nm to 1100nm. It is very suitable for photometry, colorimetry, and radiometry.
Calibration of imaging luminance measuring devices (ILMD)
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A method of calibration of imaging luminance measuring devices has been studied. By the device-independent color space transformation, the color image by digital camera could be converted to the CIE's absolute color space lab. Then, the calibration model is fitted between ln(L/t) and luminance. At last, luminance image is obtained and the dynamic range of luminance image could be adjusted by shutter speed.
Evaluating the uncertainty of the fiber spectroradiometer
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The fiber spectroradiometer is now widely used in the photometry and radiometry due to the convenience. Before use the calibration is usually traced back to the tungsten lamp with known spectral irradiance. However, the working condition may differ greatly from the calibration condition, such as the signal level, the spectrum shape, and et al. In the experiment, characteristics of the fiber spectroraidometer are investigated, such as the short time stability, the nonlinear phenomena due to the integration time and signal level. Uncertainty of the calibration is evaluated taking all the factors into account.
Spectral-based inferential measurement of grey-body’s temperature
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Aiming at the problems of temperature measurement and the defects of radiance thermometry theory, one method of spectral-based inferential measurement is proposed, which adopts the Empirical Risk Minimization (ERM) functional model as the temperature measurement model. Then, the radiance thermometry theory and inferential measurement technology are discussed comparatively. Temperatures of some targets, such and tungsten lamp and solar surface, are measured by spectral-based inferential measurement.
Optical tomographic scanning target-tracking system based on single pixel sensor
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Optical tomography imaging had the characteristics of high resolution. The rotating periscope system and modulating plate with 65 slits were designed. Filter back projection (FBP) algorithm was applied to the one-dimensional signals, which were obtained by multi-angle scanning in modulating plate, to reconstruct two-dimensional image. Single pixel photoelectric sensor has high frequency response and can acquire high speed real-time signal. This work had carried on the simulation and experiment about scanning system based on the analysis and determination about the modulating plate’s parameters, and verify the feasibility of scanning system. In this paper, the method plays an important role in developing novel target tracking system and provides deep foundation for deeper experimental research.
Research on motion model for the hypersonic boost-glide aircraft
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A motion model for the hypersonic boost-glide aircraft(HBG) was proposed in this paper, which also analyzed the precision of model through simulation. Firstly the trajectory of HBG was analyzed, and a scheme which divide the trajectory into two parts then build the motion model on each part. Secondly a restrained model of boosting stage and a restrained model of J2 perturbation were established, and set up the observe model. Finally the analysis of simulation results show the feasible and high-accuracy of the model, and raise a expectation for intensive research.
A new classification algorithm based on multi-kernel Support Vector Machine on infrared cloud background image
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A new classification algorithm based on multi-kernel support vector machine (SVM) was proposed for classification problems on infrared cloud background image. The experimental results show that the method integrates the advantages of polynomial kernel functions, Gaussian radial kernel functions and multilayer perception kernel functions. Compared with the traditional single-kernel SVM classification method, the proposed method has better performance both in local interpolation and global extrapolation, and is more suitable for SVM classification problems when the training sample size is small. Experimental results show the superiority of the proposed algorithm..
Parameter estimation of single cloud particle based on in-line digital holography
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In terms of weather modification, detection of cloud droplet particles, which is one of the important measurements, will provides an important reference for artificial weather modification. Digital holographic technology, for that it can realize the three-dimensional particle field measurement and get detail parameters of particle, is widely used in particle measurement along with the high development of modern high resolution CCD and computer technology. In this text , particle of cloud droplet simulated in the laboratory were recorded. By using the in-line digital holographic to obtain the digital holographic image of cloud droplets particles, and single feature parameters (including the shape, size, ovality) of the cloud droplets particles by calculating . It laid a foundation for the future research of cloud group particle characteristics of particle field.
Intrinsic fluorescence spectra characteristics of vitamin B1, B2, and B6
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This paper presents the intrinsic fluorescence characteristics of vitamin B1, B2 and B6 measured with 3D fluorescence Spectrophotometer. Three strong fluorescence areas of vitamin B2 locate at λex/λem=270/525nm, 370/525nm and 450/525nm, one fluorescence areas of vitamin B1 locates at λex/λem=370/460nm, two fluorescence areas of vitamin B6 locates at λex/λem=250/370nm and 325/370nm were found. The influence of pH of solution to the fluorescence profile was also discussed. Using the PARAFAC algorithm, 10 vitamin B1, B2 and B6 mixed solutions were successfully decomposed, and the emission profiles, excitation profiles, central wavelengths and the concentration of the three components were retrieved precisely through about 5 iteration times.
Research of laser echo signal simulator
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Laser echo signal simulator is one of the most significant components of hardware-in-the-loop (HWIL) simulation systems for LADAR. System model and time series model of laser echo signal simulator are established. Some influential factors which could induce fixed error and random error on the simulated return signals are analyzed, and then these system insertion errors are analyzed quantitatively. Using this theoretical model, the simulation system is investigated experimentally. The results corrected by subtracting fixed error indicate that the range error of the simulated laser return signal is less than 0.25m, and the distance range that the system can simulate is from 50m to 20km.
Optimal design of resonant enhanced quantum dot infrared photodetector based on metal-insulator-metal microcavity
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The design of quantum dot infrared photodetector (QDIP) based on metal-insulator-metal (MIM) microcavity in which the quantum dot (QD) is sandwiched between a planar metallic film and a metallic stripe is reported. By a finite difference time-domain (FDTD) method, the light coupling efficiency spectra and enhancement factor are numerically calculated. The results exhibit that the total electric field concentrated in metal-metal region is strongly enhanced when the resonant frequency of microcavity is equal to the QD’s peak response frequency. This enhancement effect mainly originates from the resonant coupling of incident photons into microcavity forming the surface plasmonic mode. The optimization of structural parameters for MIM microcavity is discussed, demonstrating an optimal structure of quantum dot infrared photodetector with the coupling efficiency improved nearly 7 times compared with conventional mesa QDIPs. So, it is deduced that a favorable performance of device such as high quantum efficiency and infrared responsivity is possible. Finally, the detector shows the potential application in the infrared sensing and imaging, as well as integrating with other electronic and optoelectronic device for the sub-wavelength size.
The influence of SNR on MTF measurement
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The Modulation Transfer Function (MTF) is a fundamental imaging system design specification and system quality metric often used in remote sensing. The MTF describes the attenuation of sinusoidal waveforms as a function of spatial frequency. Practically, MTF is a metric quantifying the sharpness of the reconstructed image. The Knife-Edge method is becoming widely applied for its advantage of simplified target and accurate computer calculation. Noise in CCD image system is inevitable, thus the SNR becomes a factor influencing the MTF measurement. In this paper, we build relationships between SNR, luminance and MTF. In conclusion, SNR is related with luminance levels linearly. SNR rises with increasing luminance. The higher SNR, the more curves conform to the theoretical MTF.
Fusion of infrared and visible images based on discrete wavelet transform
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In the view of the situation that single-sensor image cannot fully reflect the scene information efficiently. A fusion method of infrared and visible images based on discrete wavelet transform is presented and comparatively analyzed with traditional methods. Firstly, the wavelet multi-scale decomposition technique is applied to the source images that will be fused to give a series of sub-band coefficient. Feature extraction and weighted average with adaptive weighting factors are used to process the high-frequency coefficients. A strategy of the absolute value comparing is adopted to the low-frequency coefficients. Finally, the fusion image is reconstructed by multi-scale wavelet inversing transformation for low frequency and high frequency coefficients. Experimental results demonstrate that infrared and visible images can be more effectively fused by the algorithm presented than traditional methods.
A detection method for infrared multi-target in aerospace backgound
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Main task of the infrared search and track system is analyzing and identifying targets of airspace. But first this is needed to detect all targets in infrared image. Therefore, the multi-target detection algorithms are studied and we propose an effective multi-target detection method. Firstly, an improved morphological operator is designed based on airspace background and target traits of infrared image. Background is weakened but targets are enhanced when infrared image is processed by the gray morphological filter. Then, potential targets are found by the maximum local sum algorithm. Finally, true targets are affirmed based on data association of sequence images. The infrared images got from long-wavelength infrared camera are processed with the method of the paper. Experiment results show that the method can detect targets in infrared image quickly and accurately.
Improved optical flow motion estimation for digital image stabilization
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Optical flow is the instantaneous motion vector at each pixel in the image frame at a time instant. The gradient-based approach for optical flow computation can’t work well when the video motion is too large. To alleviate such problem, we incorporate this algorithm into a pyramid multi-resolution coarse-to-fine search strategy. Using pyramid strategy to obtain multi-resolution images; Using iterative relationship from the highest level to the lowest level to obtain inter-frames’ affine parameters; Subsequence frames compensate back to the first frame to obtain stabilized sequence. The experiment results demonstrate that the promoted method has good performance in global motion estimation.
Design and research of spectropolarimetric system based on Sagnac interferometer
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Spectral imaging technology has made great achievements in applications of earth observation and space target detection, with the further development of research, the requirement that People tend to get more material properties about target is also improving rapidly, so getting more characters of the target is continuous pursuit goal for the instruments of optical remote sensing. Polarization is one of the four main physical properties of light including intensity, frequency and phase . It has very important significance for remote sensing observations such as improving the accuracy of target recognition. This paper proposes on a spectropolarimeter system based on Sagnac interferometer, and introduces the main aspects related to System components, working principle, optical design, adaptive spectrum extraction algorithm, state of polarization extraction methods. Also get the data of polarization spectral imaging by using the instruments designed by the principle .By processing these data I have got the combined polarization image and target spectral curves, achieved a good result. It is a new attempt to obtain polarization spectral image by integrated measuring system. Then thoroughly solve the traditional shortcoming of spectropolarimeter, such as asynchronous detecting, poor stability and vibration, poor energy efficiency. It can be applied to many kinds of fields. Simultaneously the paper puts forward some relevant new points in the future research for this kind of principle.
Visible polarization image fusion with non-subsampled Shearlets
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For the disadvantage of traditional target detection methods with low detection rate and difficulties in distinguishing the small temperature difference and camouflage targets, this paper presents a kind of visible polarization image fusion method using non-subsampled Shearlets transform. Firstly, we obtain four polarization status images by multi-detector camera, where the direction of polarization angle is 0° 、45°、90°、135° separately. The Stokes vectors are calculated by polarization status images. Then, the extracted target polarization feature images and light intensity image are decomposed into several sub frequency bands by NSST with fine multi-scale decomposition characteristics. Meanwhile, the fusion coefficients are determined based on high-frequency energy window and low-frequency mean in the frequency domain. At last, the final fusion image is obtained after NSST inverse transform and target enhancement. Experimental results illustrate that the proposed approach could obtain better fusion images with rich details, high contrast, highlighting the polarization characteristic of the target to improve the ability of scene perception and target detection.
Optoelectronic date acquisition system based on FPGA
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An optoelectronic date acquisition system is designed based on FPGA. FPGA chip that is EP1C3T144C8 of Cyclone devices from Altera corporation is used as the centre of logic control, XTP2046 chip is used as A/D converter, host computer that communicates with the date acquisition system through RS-232 serial communication interface are used as display device and photo resistance is used as photo sensor. We use Verilog HDL to write logic control code about FPGA. It is proved that timing sequence is correct through the simulation of ModelSim. Test results indicate that this system meets the design requirement, has fast response and stable operation by actual hardware circuit test.
The extended depth of field microscope imaging system with the phase pupil mask
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A ‘0/π’ phase pupil mask was developed to extend the depth of field of a circularly symmetric optical microscope imaging system. The modulation transfer function curves, the normalized point spread function figures and the spot diagrams of the imaging system with the optimal mask were analyzed and simulated. The results show that the large depth of field imaging system with the ‘0/π’ phase pupil mask has a high resolution in a long frequency band and can obtain clear images without any post-processing. The experimental results also demonstrate that the depth of field of the imaging system is extended successfully.
Study on evaluation of photoelectric jamming effectiveness on ranging lidar
Jinxi Che,
Haiqiang Yang,
Bo Gao
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Lidar (Light Detection and Range) is a brand-new field and research hotspot. Ranging lidar is studied in this paper. Specifically, its basic working principle and photoelectric jamming mechanism are introduced. Then, the ranging error jamming success rate rule is developed for laser distance deception jamming. And the effectiveness evaluation of laser blinding jamming is based on the influence level on ranging accuracy and ranging function. The results have some reference value to evaluation of jamming test effectiveness.
Research on an imaging spectropolarimeter
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Imaging spectropolarimetry has been explored as a method that increment in our capability to respond to existing requirements, as well as to our insatiable need for more information in remote sensing applications. Spectrometry enables detailed comparison of target and background spectra. The polarimetric state of received radiation contains valuable information about source object surface roughness and orientation, it has the potential to highlight manmade objects despite spectral camouflage. A laboratory breadboard spectropolarimetric system has been design for operation in the visible waveband to demonstrate the potential of this technique for future airborne and spaceborne systems. The experiment setup and some experimental results are presented in this paper.
Resolution characteristics of graded doping and graded composition reflection-mode AlGaAs/GaAs photocathodes
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The resolution model of graded doping and graded composition reflection-mode AlGaAs/GaAs photocathode is solved numerically from the two-dimensional continuity equations. According to the model, the theoretical modulation transfer functions (MTFs) of different structure reflection-mode photocathodes were calculated, and the effects of doping concentration, Al composition, AlGaAs and GaAs layer thickness on the resolution of cathodes were analyzed. The simulation results show that both graded composition and graded doping structures can increase the resolution of photocathode, and the effect of graded composition structure is more pronounced. The resolution improvement is attributed to the built-in electric field induced by a graded composition or doping structure. The simulation results also show that the MTFs of cathodes are affected by the AlGaAs and GaAs layer thickness.
The phase diversity and the phase retrieval
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Measuring optical wave-fronts precisely is a difficult task because detectors directly sense intensity, not phase. The most common method of measuring the phase uses an interferometer that creates an intensity distribution from which the phase of the field can be determined more easily. In order to overcome the wave-front distortion caused by atmosphere turbulence and optical system aberration, the system of wave-front solutions based on the focal plane image information can be used in the optical system in-line detection. The realizations of phase solver technology mainly include phase diversity and phase retrieval. So, this paper mainly explains phase diversity and phase retrieval.
Methods of generating a hollow spot for STED microscopy
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On the base of the vectorial diffraction theory, the diffraction integral represents are obtained to generate a hollow spot for STED. In the paper, the incident light is modulated by phase and polarization to focus a hollow spot. The 2-dimension hollow spot is obtained by modulating the circularly polarized beam with 0-2π vortex phase or 0/π circular phase. Addition In addition, we get the 2-dimension hollow spot by focusing azimuthally polarized beam or a radially polarized beam modulated with 0/π circular phase. The intensity distributions and size of these 2-dimension hollow spots are discussed. Then the 3-dimension hollow spot is got by taking advantage of two kinds of 2-dimension hollow spots. There are two methods to generate a hollow spot by the diffraction integral represents. One is modulating two circularly polarized beams with 0-2π vortex phase and 0/π circular phase respectively. The other is choosing an azimuthally polarized beam and a radially polarized beam modulated with 0/π circular phase as depletion beams. So we obtain a 2-dimension hollow spot by modulating a beam, and obtain a 3-dimension hollow spot by modulating two beams. These hollow spots can be useful for STED to realize 2-dimension and 3-dimension super-resolution.
Luminescent sensing of dissolved oxygen based on Ru(II) complex embedded in sol-gel matrix
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In biological cells and tissues environment, real-time monitoring and controlling dissolved oxygen (DO) provides critical information for studying cellular metabolism process, health status and pathological features. This paper developed an optical DO sensor based on fluorescence quenching principle, prepared tris(4,7-diphenyl-1,10- phenanthroline)ruthenium(II) dichloride complex sol-gel sensing film, and studied its sensing performance. The principle of this sensor is that dissolved oxygen has quenching effect towards the fluorescence emitted by ruthenium complex. So the fluorescence intensity is reduced due to the existence of DO. The measurement limit of DO was 10- 100%, the response time was 20s, and the resolution was 0.02. Compared to traditional dissolved oxygen electrode probe, this luminescent fiber had many advantages, such as smaller size, shorter response time and higher stability.
Gas diffusion optic flow calculation and its applications in gas cloud infrared imaging
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Motion detection frequently employs Optic Flow to get the velocity of solid targets in imaging sequences. This paper suggests calculate the gas diffusion velocity in infrared gas leaking videos by optic flow algorithms. Gas target is significantly different from solid objects, which has variable margin and gray values in diffusion. A series of tests with various scenes and leakage rate were performed to compare the effect of main stream methods, such as Farneback algorithm, PyrLK and BM algorithm. Farneback algorithm seems to have the best result in those tests. Besides, the robustness of methods used in uncooled infrared imaging may decline seriously for the low resolution, big noise and poor contrast ratio. This research adopted a special foreground detection method (FDM) and spectral filtering technique to address this issue. FDM firstly computes corresponding sample sets of each pixel, and uses the background based on the sets to make a correlation analysis with the current frame. Spectral filtering technique means get two or three images in different spectrum by band pass filters, and show a better result by mixing those images. In addition, for Optic Flow methods have ability to precisely detect directional motion and to ignore the nondirectional one, these methods could be employed to highlight the gas area and reduce the background noise. This paper offers a credible way for obtaining the diffusion velocity and resolves the robust troubles in practical application. In the meanwhile, it is an exploration of optic flow in varied shape target detection.
Real-time color imaging system for NIR and visible based on neighborhood statistics lookup table
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The near infrared radiation is the main component of the solar radiation. It's widely used in the remote sensing, nightvision, spectral detection et al. The NIR images are usually monochromatic, while color images are benefit for scene reconstruction and object detection. In this paper a new computed color imaging method based on the neighborhood statistics lookup table for NIR and visible was presented, and its implementation system was built. The neighborhood statistics lookup table was established based on the neighborhood statistical properties of the image. The use of the neighborhood statistical properties can enriched the color transmission variables of the gray image. It obtained a colorful lookup table that could improve the effects of the color transfer and make the colorized image more natural. The proposed lookup table could also transfer the color details well for the neighborhood statistical information representing the texture of the image. The results shows that this method yields a color image with natural color appearance and it can be implemented in real-time.
3D profile measurement of micro-structured array with light field microscope
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Micro-structured array is a crucial optical element with wide range of applications. The optical performance of microstructured array is determined by feature sizes of array, such as diameter, depth and the uniformity across the whole array. Those sizes can be directed retrieved from the 3D profile. We propose a 3D profile measurement system based on light field microscope, which is promising in achieving fast data acquisition by one shot. We propose the principle of measurement, develop the algorithm for focus stack calculation and 3D reconstruction. Preliminary experiments suggest the prospects and challenges.
Detection of optical properties in small region by diffuse reflectance
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The optical properties of small and highly absorbing tissues can be determined by measurement of spatially resolved diffuse reflectance at short source-detector separations. Spatial resolution and number of measuring point influence the inverting precision of optical property directly from the experimental diffuse reflectance. To increase spatial resolution and number of measuring point, a high-resolution and multiple points detection system is designed. A special optical fiber array probe is employed. Its spatial resolution is 0.125mm. The system is proved to be reliable by comparing the experimental result of diffuse reflectance from small region 0.125mm-1.25mm with that of numerical simulation. The inverting method based on Monte Carlo simulation is designed, by which optical properties can be achieved by building optical parameter date base and training artificial neural network (ANN).
Study on signal simulator for photon counting laser ranging
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This article first introduced the basic theory of photon counting laser ranging technology, then analyzed the responding and output of single photon detector. The method of simulating signals with 0/1 sequence was raised. M sequence is a random 0/1 sequence, and signals of adjustable ‘1’ scale were derived from it, which act as models of noise. This method was realized on FPGA platform and an ideal result was gained, which verified that the method put forward in this article is practical and effective.
Spectral radiance characterization and realization based on high temperature blackbody BB3500M
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New primary standard apparatus of spectral radiance was setup at National Institute of Metrology (NIM) based on high temperature blackbody BB3500M in 2011. Wavelength range was extended to 220 nm - 2550 nm. The measurement uncertainty of temperature was 0.64 K (k=1) at 2980K traceable to the Ag, Cu, Co-C, Pt-C and Re-C fixed point blackbodies, and checked by a WC-C fixed point blackbody. Good consistency was obtained by using two different imaging optics with varied solid angle and different object distances, the relative deviation is less than ±0.4 % at all wavelengths. A set of characteristic experiments were designed and analyzed in this paper, such as alignment error and the influence of the different shape and size of the water-cooled precise aperture, the polarization effects etc. NIM participated spectral radiance international comparison APMP.PR-S6 by using this new developed apparatus in 2014 with measurement uncertainty (k=1) 0.95% at 250nm, 0.50% at 400nm, 0.41% at 800nm, and 0.80% at 2500nm respectively.
Laser bistatic two-dimensional scattering imaging simulation of lambert cone
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This paper deals with the laser bistatic two-dimensional scattering imaging simulation of lambert cone. Two-dimensional imaging is called as planar imaging. It can reflect the shape of the target and material properties. Two-dimensional imaging has important significance for target recognition. The expression of bistatic laser scattering intensity of lambert cone is obtained based on laser radar eauqtion. The scattering intensity of a micro-element on the target could be obtained. The intensity is related to local angle of incidence, local angle of scattering and the infinitesimal area on the cone. According to the incident direction of laser, scattering direction and normal of infinitesimal area, the local incidence angle and scattering angle can be calculated. Through surface integration and the introduction of the rectangular function, we can get the intensity of imaging unit on the imaging surface, and then get Lambert cone bistatic laser two-dimensional scattering imaging simulation model. We analyze the effect of distinguishability, incident direction, observed direction and target size on the imaging. From the results, we can see that the scattering imaging simulation results of the lambert cone bistatic laser is correct.
Temperature measurement error simulation of the pure rotational Raman lidar
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Temperature represents the atmospheric thermodynamic state. Measure the atmospheric temperature accurately and precisely is very important to understand the physics of the atmospheric process. Lidar has some advantages in the atmospheric temperature measurement. Based on the lidar equation and the theory of pure rotational Raman (PRR), we’ve simulated the temperature measurement errors of the double-grating-polychromator (DGP) based PRR lidar. First of all, without considering the attenuation terms of the atmospheric transmittance and the range in the lidar equation, we’ve simulated the temperature measurement errors which are influenced by the beam splitting system parameters, such as the center wavelength, the receiving bandwidth and the atmospheric temperature. We analyzed three types of the temperature measurement errors in theory. We’ve proposed several design methods for the beam splitting system to reduce the temperature measurement errors. Secondly, we simulated the temperature measurement error profiles by the lidar equation. As the lidar power-aperture product is determined, the main target of our lidar system is to reduce the statistical and the leakage errors.
Multi-terminal remote monitoring and warning system using Micro Air Vehicle for dangerous environment
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For overcoming the problems such as remote operation and dangerous tasks, multi-terminal remote monitoring and warning system based on STC89C52 Micro Control Unit and wireless communication technique was proposed. The system with MCU as its core adopted multiple sets of sensor device to monitor environment parameters of different locations, such as temperature, humidity, smoke other harmful gas concentration. Data information collected was transmitted remotely by wireless transceiver module, and then multi-channel data parameter was processed and displayed through serial communication protocol between the module and PC. The results of system could be checked in the form of web pages within a local network which plays a wireless monitoring and warning role. In a remote operation, four-rotor micro air vehicle which fixed airborne data acquisition device was utilized as a middleware between collecting terminal and PC to increase monitoring scope. Whole test system has characteristics of simple construction, convenience, real time ability and high reliability, which could meet the requirements of actual use.
Optical design of a kind of catadioptric system
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According to the requirements of practical application, the optical parameters were calculated. In order to reduce the difficulty in engineering, the design adopted the scheme of catadioptric structure, of which all the surfaces were designed as spherical surface type. In addition, a correcting component was designed, as well as a focusing component, for the purpose of improving the image quality and focusing. The optical design software CODEV was used to optimize the scheme and simulate the result. It was shown that the design result obtained an excellent image quality within the visible wavelength range of 0.45μm- 0.75μm. At last, the design result was tested by tolerance analysis.
Design of off-axis four-mirror optical system without obscuration based on free-form surface
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With the development of modern military technology, the requirements of airborne electro-optical search and tracking system are increasing on target detection and recognition. However, traditional off-axis three-mirror system couldn’t meet the requirements for reducing weight and compacting size in some circumstances. Based on Seidel aberration theory, by restricting the aberration functions, the optical system could achieve initial construction parameters. During the designing process, decenters and tilts of mirrors were adjusted continuously to eliminate the obscurations. To balance off-axis aberration and increase angle of view, the free-form mirror was introduced into the optical system. Then an unobstructed optical system with effective focal length of 100 mm, FOV of 16°×16°, and relative aperture as F/7 is designed. The results show that the system structure is compact, with imaging qualities approaching diffraction limit.
Research on the detection capability of space camera
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Detection capability of space camera is regarded as the principal parameter in the design of space camera. On the basis of the concept of signal-to-noise ratio (SNR) and through the research of principles and derivation of theories, detection capabilities under static condition and the condition of relative motion were analyzed and compared. With a set of typical parameters given, the change of detectable magnitude with the changes of parameters was investigated. Considering the real operating environment of space camera, the necessity of temperature control in the design of space camera was discussed. The theoretical analysis provides a reference for the design of space camera.
Design and analysis of APD photoelectric detecting circuit
R. Fang,
C. Wang
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In LADAR system, photoelectric detecting circuit is the key part in photoelectric conversion, which determines speed of respond, sensitivity and fidelity of the system. This paper presents the design of a matched APD Photoelectric detecting circuit. The circuit accomplishes low-noise readout and high-gain amplification of the weak photoelectric signal. The main performances, especially noise and transient response of the circuit are analyzed. In order to obtain large bandwidth, decompensated operational amplifiers are applied. Circuit simulations allow the architecture validation and the global performances to be predicted. The simulation results show that the gain of the detecting circuit is 630kΩ while the bandwidth is 100MHz, and 28dB dynamic range is achieved. Furthermore, the variation of the output pulse width is less than 0.9ns.
Recent advances in telecommunication avalanche photodiodes with nano-sized multiplication region
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This paper reviews the recent advances in telecommunication avalanche photodiodes with nano-sized multiplication region. A new low noise avalanche photodiode based on InP traditional material has been proposed for high speed optical communication.
Structure release of silicon micro-channel based on wet etching
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Based on wet etching theory, the silicon microchannel structure after electrochemical etching was released in TMAH solution to obtain the through-hole microchannel. The silicon wafer with the different resistivity was selected as the substrate of microchannel plate, the TMAH solution was selected in mass concentration of 28.5wt%, and the SiO2 passivation layer with the thickness of 200nm was prepared by thermal oxidation for protection of side-wall of microchannel. Contrary to the problem encountered in wet etching, Firstly, the corrosion characteristics of silicon and SiO2 thin film in TMAH solution were investigated, respectively. In addition, the effects of the pH values of TMAH solution on corrosion characteristics in microstructure releasing of silicon microchannel were studied and analyzed. The experiments show that the silicon wafer with high resistivity can be easily etched, the etching rate of SiO2 film in TMAH is uniform, and adjusting the pH value of etching solution to make it constant during etching can effectively increase the corrosion rate and decrease the surface roughness of samples.
Portable detection system of vegetable oils based on laser induced fluorescence
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Food safety, especially edible oils, has attracted more and more attention recently. Many methods and instruments have emerged to detect the edible oils, which include oils classification and adulteration. It is well known than the adulteration is based on classification. Then, in this paper, a portable detection system, based on laser induced fluorescence, is proposed and designed to classify the various edible oils, including (olive, rapeseed, walnut, peanut, linseed, sunflower, corn oils). 532 nm laser modules are used in this equipment. Then, all the components are assembled into a module (100*100*25mm). A total of 700 sets of fluorescence data (100 sets of each type oil) are collected. In order to classify different edible oils, principle components analysis and support vector machine have been employed in the data analysis. The training set consisted of 560 sets of data (80 sets of each oil) and the test set consisted of 140 sets of data (20 sets of each oil). The recognition rate is up to 99%, which demonstrates the reliability of this potable system. With nonintrusive and no sample preparation characteristic, the potable system can be effectively applied for food detection.
Method of narcissus analysis in infrared system based on ASAP
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Narcissus of cooled infrared system should be controlled strictly. So, accurate and rapid analysis of narcissus is very important. Deriving the SNR of narcissus based on the definition of noise equivalent power. Using simulation software CodeV and ASAP analyses the narcissus. Screen out the optical surface whose narcissus is serious in CodeV. Then build the model of the system in ASAP and add reasonable surface properties, get the result of size and average irradiance of the image narcissus spot by real ray tracing. Calculate the SNR of narcissus by putting the value of average irradiance into front formulation. On this basis, the simulation analysis and experimental test about the Narcissus of an infrared lens were performed. The experimental result is consistent with the simulation analysis.
BOC(n,n) signal multipath mitigation using MEDLL technology
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For satellite navigation and positioning receivers are susceptible to the influence of the multipath, this paper used multipath estimating delay lock loop (MEDLL) technology for BOC (n, n) multipath signal tracking. Through the analysis of multipath signal model, it is concluded that all the multipath signal can be expressed by its amplitude, phase and delay. Then in odor to get the accurate direct signal, this paper applied MEDLL algorithm to estimate the received signal. Finally, the simulation show that this algorithm can realize multipath signal track demodulation and accurate data demodulation under a low signal noise ratio environment (SNR= -20db).
Wavefront aberrations control for complex optical systems by compensation-surface
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Figure-errors as an optical manufacture error would degrade the performance of optical system. Optical components-clocking around optical axis is a classical method of figure-errors compensation. However, the compensation ability of optical component clocking is limited by the distribution of actual figure-error. This paper proposes a compensation-surface method, which is a simple and effective method for figure-error compensation. Based on the predicted wavefront error with actual figure error, an analytical computational method of figure function of the compensation-surface is built. The figure of compensation-surface is a deterministic polished surface. Finally the other figure errors can be largely compensated by the compensation-surface. The method is implemented on a manufactured optical system, a 193nm small-field projection lens. Simulation experiment proves our method can greatly reduce the aberration caused by figure errors. The WFE can be reduced to 0.04λ (λ=193.29nm) from 0.265λ and reduced by 84%. The compensation effect is more remarkable, and nearly 2.7 times the compensation effect of optical-component clocking method.
Energy distribution in the quantum spectrum
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At first this paper summarizes the current situation and historical development of the spectrum research, the difficulties and demand background. Then it introduces the research status of quantum spectrum and research ideas of energy distribution in quantum spectrum. We explain the concept of quantum spectrum, the difference between quantum spectrum and spectrum. We elaborate energy distribution in quantum spectrum from three aspects, which are representation, feature and mechanism of quantum spectrum energy distribution. Finally we describe the application of monochrome quantum spectrum about imaging and detection aspects and give an overview of the quantum spectrum. Based on above research results we continue to study and achieve the detection of multi-spectral imaging, which provide the technical basis for the application. We try access to an advanced stage of quantum spectrum study as soon as possible.
The application of ghost imaging in infrared imaging detection technology
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Traditional imaging are mostly based on the principle of lens imaging which is simple but the imaging result is heavily dependent on the quality of detector. It is usual to increase the detector array density or reduce the size of pixels to improve the imaging resolution, especially for infrared imaging. It will decrease the light flux causing the noise enhance relatively and add the cost on the contrary. Besides, there is a novel imaging technology called ghost imaging. We present a new infrared imaging method named computational ghost imaging only using a bucket detector without spatial resolution, which avoiding the allocation of flux on the pixel dimension as well as reducing the cost.
Modeling and simulation of blazed grating based on MEMS scanning micro-mirror for NIR micro-spectrometer
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Near infrared micro-spectrometer (NIRMS) as a vital detection equipment for various elements has been investigated over the last few years. Traditional MEMS NIRMS employs CCD array detectors for NIR spectrum collection and this leads to higher fabrication cost. In this paper, to ensure the higher diffraction efficiency as well as lower fabrication cost, a novel blazed grating based on MEMS scanning micro-mirror (SMM) is proposed. By our design method, the NIRMS needs only one single InGaAs detector photo diode to collect NIR spectrum and ensure the high diffraction efficiency. Our results show that the diffraction efficiency of the blazed grating is almost 50% and the peak value reaches to 90% in the range of 900-2,100 nm while the optical scanning angle is 14.2°.
Research progress of airy beams and application prospect
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Considering the Airy beams has novel features that different from Gauss laser, which has attracted researchers’ great interest in recent years, and achieved many significant research results. From the perspective of technology and application, this paper combining with the characteristics of remote sensing summarizes the research progress of Airy beams, prospects the possible application prospect in the field of space.
The nonlinear absorption of carbon quantum dots under the picosecond laser pulse
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Using Z-scan technique to investigate the nonlinear absorption characteristics of carbon quantum dots (CDs) under the picosecond laser pulse with the wavelength of 532 nm, which the CDs’ types were same particle size of different solvent and same solvent of different particle sizes. The experimental results showed that the nonlinear absorption of water-soluble CDs of 3.9 nm was saturated absorption, and oil-soluble CDs’ was reverse saturable absorption for the same particle size, their nonlinear absorption coefficients were -2.09×10-12 m/W and 6.9×10-12 m/W, respectively; the nonlinear absorption of water-soluble CDs of 4.8 nm was reverse saturable absorption, and oil-soluble CDs’ was saturated absorption for same particle size, their nonlinear absorption coefficients were 1.9×10-12 m/W and -1.3×10-12 m/W, respectively. The experimental results indicate that the nonlinear absorptions of CDs are mainly influenced by the solvent effect and quantum size effect in the same.
Laser energy distribution on detector under the different incident angle
Y. Wang,
G. Wang,
Q. Chen,
et al.
Show abstract
Laser active suppressing jamming is one of the most important technologies in the domain of electro-optical countermeasures. The propagation direction of laser is not always in the same line with the principal axis of electro-optical imaging system, so it is necessary to investigate laser energy distribution on detector under the different incident angle. This paper toke optical system with wide field of view for example. We firstly analyzed the system’s structure based on the inverting prism and evaluated image quality. Laser energy distribution caused by diffraction effect of optical system was secondly simulated based on Kirchhoff ’s diffraction theory. Thirdly, we built the system’s analysis model of stray light, traced a large number of light propagation, and obtained laser energy distribution on detector caused by scattering effect. At last, combine the above two kinds of energy distribution into total laser energy distribution on detector. According to the detector’s saturated threshold, we can count up the saturated number and evaluate laser disturbing effect. The research results can provide theoretical reference and technical support for evaluating laser disturbing effect of electro-optical imaging system.
Analysis on electromagnetic characteristics and military application of non-magnetized discharge plasma
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Firstly, the dispersion equation of a plane electromagnetic wave in homogeneous and non-magnetized discharge plasma was established. According to the different frequency of electromagnetic wave and plasma parameters, the characteristics were discussed when the plasma interacted with electromagnetic waves. Then the gas discharge approach was put forward according to characteristics of plasma generated by different methods and their advantages and disadvantages. The possibility of using non-magnetized discharge plasma for the military purpose was analyzed. In the end, the principle and characteristics of the application of the non-magnetized discharge plasma were studied in the fields of stealth and protection against strong electromagnetic pulse.
Design of camouflage material for visible and near infrared based on thin film technology
Lei Miao,
Jia-ming Shi,
Da-peng Zhao,
et al.
Show abstract
Visible light and near infrared based camouflage materials achieve good stealth under traditional optical detection equipment，but its spectral differences with green plants can be taken advantage of by high spectrum based detection technologies. Based on the thin structure of bandpass filter, we designed an optical film with both green and near infrared spectrum. We conducted simulations using transfer matrix methods and optimized the result by simplex methods. The spectral reflectance curve of the proposed thin film matches that of green plants, and experiments show that the proposed thin film achieve good invisibility under visible light and near infrared in a wide viewing angle.
A method for interfere elimination of structured light cameras
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In this paper, a method to eliminate the interference of the-structured light cameras is presented. 3D reconstruction is a key procedure of 3D technologies. The depth information is significant for 3D reconstruction of a certain scene and the depth camera based on structured light is widely used. This kind of cameras can get the depth information of a certain scene by emitting a beam of structured light and capture it after reflection. In order to enlarge the range of 3D reconstruction, more than one depth-cameras are used simultaneously in one scene. However, when working together, the lights emitted by those cameras would overlap in the scene. The light pattern captured by the cameras would be interfered by others and the depth they calculated would be wrong correspondingly. The method presented in this paper abstracts the progress of modulation and demodulation to a modulation matrix. Based on that, this paper provides a procedure of the whole process of interference elimination. We also optimize the matrix based on the thought of interfere alignment. Finally, the result of simulation was presented and verify the efficiency of the method.
An evaluation methodology for long-range jammer to CCD
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By analyzing the factors of laser transmission from long-range jammer to CCD in the distribution of laser at the entrance of optical system of CCD, an evaluation methodology was established which utilized the ATP error data and the distribution of laser through turbulent atmosphere together and could get the jamming probability which could be used to get evaluation result. A conversion method was devised to convert test data to simulation data of ATP. Based on circular aperture Fraunhofer diffraction theory, a simplified model that only used the central bright patch was provided to convert the relationship between the number of saturated pixel and the incident laser energy by testing to the relationship in simulation. Some advice was given for the usage of test data of ATP and the relationship between the number of saturated pixel and the incident laser energy by testing to make sure that the data is available.
THz Technology and Application
Research on the shape error from the Gaussian moth-eye antireflection microstructure elements made by the laser interference lithography technology
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The contour shape of the Gaussian moth-eye antireflection microstructure elements is relied on the manufacturing method, the laser interference lithography technology, also effecting its’ reflectivity. This paper gives out the reflectance characteristics of the Gaussian moth-eye antireflection microstructure elements made on the monocrystalline silicon substrate at the mid-infrared with the method of RCWA. We analyzes the different influences on the reflectivity from the cycle, trench depth, wavelength and refractive index by the way of univariate. At last getting the result by MATLAB simulation: the reflectivity become least at the 1.7μm when the cycle between 1~3μm, about 0.05%; the largest reflectivity is about 14%, when the cycle is 1μm. Similarly, the trench depth has great influence on the reflectivity, the reflectance decreased and stabilized with growing of the trench depth. At the same time, the wavelength has influence on the reflectivity. These conclusions is beneficial to designing Gaussian moth-eye antireflection microstructure elements. The conclusion is got that when the angle of incidence different, the azimuth influences the reflectivity.
Topology optimization design of a space mirror
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As key components of the optical system of the space optical remote sensor, Space mirrors’ surface accuracy had a direct impact that couldn’t be ignored of the imaging quality of the remote sensor. In the future, large-diameter mirror would become an important trend in the development of space optical technology. However, a sharp increase in the mirror diameter would cause the deformation of the mirror and increase the thermal deformation caused by temperature variations. A reasonable lightweight structure designed to ensure the optical performance of the system to meet the requirements was required. As a new type of lightweight approach, topology optimization technology was an important direction of the current space optical remote sensing technology research. The lightweight design of rectangular mirror was studied. the variable density method of topology optimization was used. The mirror type precision of the mirror assemblies was obtained in different conditions. PV value was less than λ/10 and RMS value was less than λ/50(λ = 632.8nm). The results show that the entire The mirror assemblies can achieve a sufficiently high static rigidity, dynamic stiffness and thermal stability and has the capability of sufficient resistance to external environmental interference . Key words: topology optimization, space mirror, lightweight, space optical remote sensor
A new method of equalizing the optical power by a liquid crystal-based tunable encoder/decoder in SAC-OCDMA PON
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A new method of equalizing the optical power is proposed to enhance the performance in the SAC OCDMA PON. The method is to use a tunable liquid crystal-based tunable encoder for further development by voltage controlling individually, so it is achieved in one device for encoding and power equalization, the experimental results show that the system BER and eye diagram are greatly improved. Since the method does not use additional devices in the condition, the system are lower complexity and cost-effective.
Qualitative identification of group composition in crude oil from different oil fields using terahertz time-domain spectroscopy
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Optical properties of the group components in crude oil were studied using terahertz time-domain spectroscopy (THz-TDS) under nitrogen environment at ambient temperature. The group composition of crude oil from different oil fields were analyzed on the basis of terahertz spectra. Both time delay and amplitude of terahertz wave were modulated in accordance with group composition. The features of terahertz spectra which contain information from different parts of the crude oil group composition can be qualitatively analyzed to detect the group components of the crude oil.
Vertical coupling and polarization-independent subwavelength grating beam splitter based on silicon-on-insulator
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We describe a novel beam splitter with advantages of a single-layer, compact and vertical coupling structure, which is based on Bragg diffraction conditions and phase match equation. FDTD method is used to optimize the design of beam splitter. The result of simulation shows that both polarizations incident light are separated into two beams of nearly equal power (near 43% split and 45% split, respectively), which are coupled into opposite directions in the waveguide. For TE mode, the coupling efficiency of the right direction and the left direction are 42.54% and 43.68, respectively. That of TM mode is 46.03% and 44.07%, respectively. The power difference for two polarizations of two output port is less than 1% and 2%, in addition, 40nm and 65nm bandwidth is achieved.
Optical properties of traditional ceramic with different sintering temperatures in terahertz range
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Terahertz spectroscopy was used to study the sintering process of traditional ceramic by scanning sample with different final temperatures (from 100-1450°C). Absorption coefficient (α) and refractive index (n) were obtained with different final temperatures. The sintering process was divided into four stages on the basis of α and n, which characterized the ceramic sintering process well. The results coincide with the actual situation. Therefore, THz-TDS represents a promising technique to monitor the synthesis process of materials.
Micro-antennas for the phase and amplitude modulation of terahertz wave
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Based on the localized surface plasmons (LSPs), a series of C-shaped slits antennas are designed to modulate the phase and amplitude of the cross-polarized transmitted wave in THz waveband. By adjusting the structure parameters of the antenna unit, arbitrary phase and amplitude modulation of the cross-polarized THz wave can be obtained. The C-shaped slit antenna units are designed at two operating frequencies f=0.8 THz and f=1.0 THz using a commercial software package (Lumerical Solutions), which is based on the finite-difference time-domain method. According to the simulated results, principles for modulating the phase and amplitude of THz wave are summarized as follows. Firstly, the operating wavelength depends on the effective length of the antenna and the operating wavelength increases as the effective length increases; Secondly, the phase of the cross-polarized wave can be modulated from 0 to 2π by changing the opening angle of the split; Thirdly, the amplitude transmittance of the cross-polarized wave can be changed from the extinction state to the maximum value by rotating the symmetry axis of the C-shaped slit. These principles can be used to direct the design of the field modulator in any other working frequency.
Non-invasive detection of murals with pulsed terahertz reflected imaging system
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Pulsed terahertz reflected imaging technology has been expected to have great potential for the non-invasive analysis of artworks. In this paper, three types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by a pulsed terahertz reflected imaging system. These preset defects include a circular groove, a cross-shaped slit and a piece of “Y-type” metal plate built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. Additionally, three-dimensional analyses have been performed in order to reveal the internal structure of defects. Terahertz reflective imaging can be applied to the defect investigation of the murals.
The technology and development trend of special optical fiber applied on the sea
X. J. Zhang
Show abstract
Combined with the international submarine cable system, fiber optic guidance technology, as well as the development of the optical fiber hydrophone in recent years, the paper clarified the required properties of optical fiber technology for special optical fiber applied on the sea, and briefly analysis development direction of the low loss, small size and bending resistant optical fiber.
Pattern conversion prediction about low water content water-oil flow based on terahertz time domain spectroscopy
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This paper aims at presenting an approach for the experimental flow pattern conversion prediction. The water-diesel mixture flowed in the horizontal square tube with water contents of 0, 0.7%, 1.5%, 2.0% and 2.3%, respectively. After the mixture flowed steadily, the sample cell, in horizontal direction, was transmitted by the terahertz radiation and the terahertz time domain spectra were obtained for all the water-diesel mixtures. There is a critical velocity VT to all of the mixtures. If the flow rate is slower than VT, the mixtures flow with water bubbly pattern, however, the mixtures will flow with the water foggy pattern and the loss of the THz ray increased rapidly when the rate is faster than VT. Consequently, the mixture pattern conversion can be predicted by detecting the turning point of the THz ray loss.
Lifetime of photo-excited carriers in GaAs studied with optical-pump terahertz-probe method
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The ultrafast photoconductive characteristics of GaAs were investigated by the optical-pump terahertz-probe (OPTP) method at room temperature. In our experiment, a significant decrease of the terahertz transmittance has been observed when the time delay between the optical pump pulse and the terahertz probe pulse was adjusted. When the optical excitation occurred on the surface of GaAs, the free carriers increase. Results regressed the experimental curve and obtained the carrier lifetime is 681ps.
Electrically tunable liquid-crystal Fabry-Perot device for terahertz radiation
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In this paper, we will present a smart structure based on an electrically controlled liquid crystal (LC) Fabry-Perot to achieve terahertz (THz) filter, which has extremely potential in THz communication. This proposed structure doesn’t need any mechanical movements because of adapting LC as a key material to compose the Fabry-Perot device. The THz filter based on LC, which is smart, light and cheap, can be realized to solve that common problem of short of tunable devices in THz radiation. The chosen LC material is E7, which has very stable and good transmissions in THz range. Under the external applied voltage, the alignment of the nematic LC allows the refractive index of the device to be tuned. Because of this feature, the resonant peaks could be shifted by changing the applied voltage. Especially, when the alignment is changed from planar to phototropic, the maximum value of the shift could be realized. The simulation result of the proposed device could be got. And the optimal structural parameters could be also got. Numerical analyses results have shown that the proposed structure has a high narrow transmission band and very sharp edges. This THz filter is novel for compact and smart features, so this kind of proposed THz filter is very attractive in many applications, such as THz communication, and THz spectral imaging.
0.3THz wireless communication systems for space applications
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Contrary to the terahertz (THz) applications on the ground, the space applications in the atmosphere free environment do not suffer the atmosphere attenuation. In this study, a 0.3 THz wireless communication systems designed for potential space applications has been set up. It consists of transmitter and detector units based on Schottky diode mixers technology. The system performance is shown including the received signal levels and Eb/N0. For demonstration of THz communications, HD video signals have been transmitted over a distance of 14 m at the data rate of 1.5Gbps.
Influence on the characteristics of THz radiation from the inductance of photoconductive antenna circuit
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By adding different inductance to the bias voltage circuit of the photoconductive antenna, the changes of the time-domain waveform peak value and spectral bandwidth of THz radiation from the photoconductive antenna were observed, and further studied the influence on the characteristics of THz radiation from the inductance of photoconductive antenna circuit when designing the photoconductive antenna. According to the experiments, it is found that different inductance values have no prominent effect on the peak value of time-domain waveform and spectrum bandwidth of THz radiation from the photoconductive antenna.
Application of threshold estimation for terahertz digital holography image denoising based on stationary wavelet transform
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Terahertz digital holography imaging technology is one of the hot topics in imaging domain, and it has drawn more and more public attention. Owing to the redundancy and translation invariance of the stationary wavelet transform, it has significant application in image denoising, and the threshold selection has a great influence on denoising. The denoising researches based on stationary wavelet transform are performed on the real terahertz image, with Bayesian estimation and Birge-Massart strategy applied to evaluate the threshold. The experimental results reveal that, Bayesian estimation combined with homomorphic stationary wavelet transform manifests the optimal denoising effect at 3 decomposition levels, which improves the signal-to-noise and preserves the image detail information simultaneously.
The meat freshness detection based on terahertz wave
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Terahertz (THz) spectroscopy has fingerprint features for many bio-molecules with frequency between infrared and microwave covering the vibrational models of a great number of materials. In this study, THz-TDS was used to detect the preserved and bad meat. And the absorption coefficient indices of bad meat and preserved meat were measured in the range of 0.2–1.0 THz. The result shows that there are differences of pork tissue in both time domain and absorption coefficient in the process of deterioration. Then differences between preserved and bad meat were also presented. In order to investigate the relationship between the terahertz characteristics and meat quality, the changes of water content and material in the samples were also discussed. This work supplies reference for the application of THz technology in meat quality detection.
Blind spectral unmixing in terahertz domain using nonnegative matrix factorization
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Recovering component spectra from terahertz measurements of unknown mixtures has been studied in this paper using nonnegative matrix factorization (NMF). NMF mathematically decomposes the spectra data into two nonnegative matrixes which describe the component spectra and the corresponding fractional abundance. Two basic algorithms in the class of this method, NMF and NMF with smoothness constraint (cNMF), were adopted to resolve the terahertz absorption spectra matrix obtained from a ternary mixture with varying compositions of Nitrofurantoin, L-Leucine and D-Tyrosine. The quality of the decomposition results was evaluated. The performance of the two algorithms on extracting component terahertz spectra was compared. The optimal result reached by cNMF in this study implies the capability of the NMF method for blind terahertz spectral unmixing. The attempt made in our work helps to further investigate unknown mixtures by terahertz spectroscopy.
The research on the optimum working conditions of photoconductive antenna
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The photoconductive antenna (PCA) is one of the most common devices to generate terahertz (THz) wave, whose radiation efficiency is largely determined by the working conditions. In order to improve the power of THz wave, the influence of pump laser and bias voltage on the intensity of the THz wave radiated by PCA was studied through experiment and the optimum working conditions of PCA was obtained through the theoretical analysis, these are the maximum safe voltage and saturated laser energy. Only under the optimum conditions can the signal-to-noise ratio(SNR)of THz wave radiated by PCA be the highest and the PCA would not breakdown.
Analysis of high voltage dielectric insulation materials of XLPE by THz-TDS system
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In this paper, cross-linked polyethylene (XLPE) was analyzed by THz time domain spectroscopy (TDS) system at room temperature. By recording time domain signal of terahertz radiation field, frequency spectrum can be obtained by Fourier transform. Then the refractive index and dielectric constant in THz band are calculated. This proves that the THz-TDS system has a potential application for detecting the aging characteristic of XLPE.
The design, test, and application of the front end in 0.3THz wireless communication systems
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Designed for space application, the paper presents the design, test and application of the front end in 0.3THz wireless communication. After test and fabrication, the terahertz wireless system is completed and indicates that HD video signals have been transmitted over a distance of 14m at the data rate of 1.5Gbps. The study shows the overall course of the test and application of the front end in wireless communication.
Classification and identification of amino acids based on THz spectroscopy
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Amino acids are important nutrient substances for life, and many of them have several isomerides, while only L-type amino acids can be absorbed by body as nutrients. So it is certain worth to accurately classify and identify amino acids. In this paper, terahertz time-domain spectroscopy (THz-TDS) was used to detect isomers of various amino acids to obtain their absorption spectra, and their spectral characteristics were analyzed and compared. Results show that not all isomerides of amino acids have unique spectral characteristics, causing the difficulty of classification and identification. To solve this problem, partial least squares discriminant analysis (PLS-DA), firstly, was performed on extracting principal component of THz spectroscopy and classifying amino acids. Moreover, variable selection (VS) was employed to optimize spectral interval of feature extraction to improve analysis effect. As a result, the optimal classification model was determined and most samples can be accurately classified. Secondly, for each class of amino acids, PLS-DA combined with VS was also applied to identify isomerides. This work provides a suggestion for material classification and identification with THz spectroscopy.
Detection of iron corrosion by terahertz time-domain spectroscopy
Hui Zhao,
Di-bo Wu,
Hong-lei Zhan,
et al.
Show abstract
The iron tablets, which were exposed in salt spray with different periods, were investigated in the 0.2~2.0 THz using reflection-type terahertz time-domain spectroscopy (THz-TDS) in vacuum environment at room temperature. The sample signals are attenuated in comparison to the reference signals with increasing the corrosion time. The THz spectroscopy peak EP and reflectivity (R) of samples strongly depended on corrosion time t with EP ∝ t-1 and R ∝ t-1. The THz characteristics of iron sheets in salt spray indicate that reflection THz-TDS will contribute to the development of non-destructive testing of corrosion in pipelines.
Polarization-dependent focusing of terahertz surface plasmon polaritons
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Focusing of terahertz (THz) surface plasmon polaritons (SPPs) excited by linearly and circularly polarized THz radiation is investigated experimentally and theoretically. A high-speed THz-SPPs imaging system is built up to measure both the amplitude and phase of the excited THz-SPPs. For the horizontally polarized THz radiation, the THz-SPPs will be focused in the centre of the semicircular slit and the phase images reveals a π/2 Gouy phase shift though the focal spot of THz-SPPs. With the illumination of vertically polarized THz radiation, the focal spot in the centre will split into two focal spots in the y-direction. For the circularly polarized incident THz radiation, the focal spot of THz-SPPs will shift upward or downward in the y-direction. FDTD simulations are performed and compared with the experimental results. A good agreement between experimental results and simulation results can be found.
Terahertz metrology on power, frequency, spectroscopy, and pulse parameters
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Terahertz metrology is becoming more and more important along with the fast development of terahertz technology. This paper reviews the research works of the groups from the physikalisch-technische bundesanstalt (PTB), National institute of standards and technology (NIST), National physical laboratory (NPL), National institute of metrology (NIM) and some other research institutes. The contents mainly focus on the metrology of parameters of power, frequency, spectrum and pulse. At the end of the paper, the prospect of terahertz metrology is predicted.
The research of multi-wavelength fiber laser mode competition suppression technology
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Multi-wavelength fiber laser has received more and more attention due to its high quality output laser, good heat dissipation, compact structure, strong resistance to electromagnetic interference. The key of multi-wavelength fiber laser is the suppression of mode competition. In this paper, multi-wavelength fiber laser mode competition suppression technologies have been studied and analyzed.
Front Matter: Volume 9795
Front Matter: Volume 9795
Show abstract
This PDF file contains the front matter associated with SPIE Proceedings Volume 9795 including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.