2019 Vol. 40, No. 2

Oe System and Engineering
Compression light field reconstruction and depth estimation
LIU Xiaomin, MA Zhibang, WANG Qiancheng, DU Mengzhu, ZHU Yunfei, MA Fengying, LIANG Erjun
2019, 40(2): 179-185. doi: 10.5768/JAO201940.0201001
Aiming at the problem of large amount of the light field data and inaccurate depth estimation at the edge, the light field was reconstructed by compressive sensing principle and a depth estimation method based on multiple information fusion was proposed. Firstly, a 5×5 view light-field was reconstructed according to the compressed sensing reconstruction algorithm, and the refocusing was realized by moving the sub-aperture after obtaining the field data. Then, the initial depth and confidence of the scene were calculated by using the defocused response cues and correspondence response of angular patch. Finally, the image edge information was calculated, and the final depth was obtained by fusing the initial depth, confidence and edge information. The compressed light field simulation and physical reconstruction were realized, and the depth estimation of the simulated reconstruction light field and the open optical field data were also achieved. The experimental results show that the method proposed can simulate and reconstruct the 5×5 view light field data, which can be used for depth estimation. The depth estimation results of the proposed method at the edge of the scene is clear and hierarchical, which verifies the feasibility and accuracy of the depth estimation for the reconstructed light field based on compressed sensing theory.
Design of real-time control software for laser target simulation system based on RTX64
HUANG Zhanhua, LIU Kun, WANG Min, GUO Jinghui
2019, 40(2): 186-192. doi: 10.5768/JAO201940.0201002
In order to satisfy the time and position accuracy requirements of the simulated target point for the laser spot target dome projection system which takes the high-precision two-axis mechanical turret with a planar mirror as the core, a design scheme of computerized control software that running in RTX64 real-time extended system environment with high real-time and time accuracy. This design scheme combines the real-time controller area network (CAN) bus with Ethernet to realize data communication and cooperative control among subsystems. Meanwhile, the position accuracy and the time accuracy of moving target simulation are effectively improved. Keep the clock synchronization period 20 ms, in the experiment, the maximum errors of the simulated target point are 0.005 34° and 0.004 04°, respectively. The errors meet the simulation precision requirement of the laser point target spherical screen projection system, which proves that the design scheme of the real-time control software is feasible.
Opto-mechanical assembly and analysis of spectral module in visible-short wave infrared band
ZHANG Quan, LI Xin, ZHAI Wenchao, LIU Enchao, ZHANG Yanna, ZHENG Xiaobing
2019, 40(2): 193-201. doi: 10.5768/JAO201940.0201003
The spectral modules of self developed radiometer are introduced. The spectral range covers the visible-short wave infrared band(400 nm~2 500 nm).The methods of opto-mechanical assembly of spectral modules are discussed and the results of opto-mechanical assembly are analyzed. The radiometer consists of three spectral modules: the visible spectral module(400 nm~1 000 nm)(VIS for short), the near-infrared spectral module(900 nm~1 700 nm)(NIR for short), and the short wave infrared spectral module(1 600 nm~2 500 nm)(SWIR for short).The detection units of spectral module use the flat-field concave grating to diffract and focus different wavelengths, use the linear array detector to detect signals.The optical units of spectral modules consist of optical fiber, slit, assembly of reflector, assembly of grating and assembly of detector. Since the effect of opto-mechanical assembly is closely related to opto-mechanical design, the result of opto-mechanical assembly can reflect the advantages and disadvantages of opto-mechanical design. According to the characteristics of the opto-mechanical design of the spectral modules, the opto-mechanical assembly was carried out. The results of opto-mechanical assembly show that the wavelength resolution of the three spectral modules is better than 4 nm, 15 nm and 20 nm, respectively. The design indexes of the spectral module are achieved, verifying the rationality of the opto-mechanical design.
Study on spectral transfer function based on dual AOTF acousto-optic crystal
CHANG Lingying, SONG Jingjing, JIN Mengzhu
2019, 40(2): 202-209. doi: 10.5768/JAO201940.0201004
The acoustic-optic tunable filter(AOTF)-based imaging spectrometer is a new type of detection instrument that integrates image, spectrum and polarization information. The spectral transfer function of the instrument is an important indicator to measure the performance of the instrument. This paper first introduces the working principle of single AOTF-type and dual AOTF-type imaging spectrometer. Then by using the optical domain spectral transmission function, the single and dual AOTF spectral transfer functions expressed by wave number are derived, and in the working band of 400 nm~900 nm, the single and dual AOTF-type spectral transfer functions are calculated and compared.Moreover, the factors affecting the dual AOTF-type spectral transfer function are simulated and analyzed. Finally, the selection of instrument parameters are analyzed and discussed. The results show that with the parameters of the incident light polar angle of 30°and the acousto-optic interaction length of 5 mm, when the wavelengths of the working centers of the dual AOTF imaging spectrometers are equal, the spectral transfer function is improved by 68% compared to the single AOTF imaging spectrometer at the same working center wavelength; when the working center wavelengths are not equal, the dual AOTF-type spectral transfer function is not absolutely superior to the single AOTF type, and there is a critical value.
3D point cloud filtering method for pose measurement application of space non-cooperative targets
GU Yingying, WANG Li, HUA Baocheng, LIU Da, WU Yun, XU Yunfei
2019, 40(2): 210-216. doi: 10.5768/JAO201940.0201005
A point cloud feature extraction and filtering method for position and attitude(P & A) sensor of space non-cooperative target was presented, in order to filter the noise in raw point cloud obtained form laser P & A sensor and solve the problem that too many points taken part in the position and attitude computing wasted too much time. Then, using simulation method, the effectiveness of filtering the space rand noise and down-sample of point cloud was verified, and the robustness for target pose and Gauss measurement noise was tested. Finally, with the help of the all physical test platform for non-cooperative targets fly around, approach and capture, using the raw point cloud obtained from laser P & A sensor, the performance of the method in real position and attitude measurement was presented. The test results show that the algorithm achieves 93.1% down sampling of the original point cloud, saves 92.9% of the pose calculation time, which can effectively improve the efficiency of on-orbit data processing and the real-time performance of pose calculation.
Application of laser induced bias interference technology in vehicle active protection system
GAO Wei, RU Zhibing, LEI Haili, TANG Lei, GUO Yuyu
2019, 40(2): 217-222. doi: 10.5768/JAO201940.0201006
In order to effectively combat the laser guided weapons and improve the survivability of vehicle-mounted weapon systems on the battlefield, we proposed a laser induced bias interference countermeasures technology for vehicle-mounted active defense systems. According to the incoming threat information and characteristics of semi-active guided weapon systems, we discussed the feasibility of laser induced interference technique.Moreover we recorded the trajectory of the tracking system from tracking and identifying the target to starting the interference system by experimental device with synchronous forward interference mode. It is verified that the system can implement interference antagonism within 7 s and reach active protection ability.
Novel liquid float polishing technology based on non-Newtonian fluid
QIN Lin, MI Qian, LI Hong
2019, 40(2): 223-228. doi: 10.5768/JAO201940.0201007
A novel flexible liquid float polishing technique was presented through software simulation and experiment. Firstly, the fluent software was employed to analyze the flow field of the liquid float polishing model which had shear thickening effect. The flow field pressure and shear force distribution of the liquid float polishing model were obtained. The simulation results show that the liquid float polishing technology has certain shearing effect on the surface of the workpiece, and the workpiece material can be removed effectively. Then, an experimental platform was established to verify the simulation results. A kind of polishing solution based on non-Newtonian power law fluid was prepared which composed of SiO2 (particle size 12 nm) served as solvend, polyethylene glycol (molecular weight of 200) served as solvent, and the cerium oxide with a mass fraction of 18% is also added as the abrasive. The surface roughness of K9 glass can be effectively reduced from 23.97 nm to 1.023 nm after 90 min polishing by using the novel flexible liquid float polishing technique. The experimental results show that this technology can be used for the processing of optical components.
Ultra-fast terahertz time domain spectroscopy system
ZHANG Hongfei, SU Bo, HE Jingsuo, ZHANG Cunlin
2019, 40(2): 229-232. doi: 10.5768/JAO201940.0201008
Ultra-fast terahertz time-domain spectroscopy(THz-TDS) system operates based on the principle of high-speed asynchronous optical sampling. The system uses two femtosecond oscillators whose repetition frequencies can vary around 1 GHz, and uses a high-bandwidth feedback circuit to control the repetition frequencies. There is a difference of Δf in the repetition frequency between two femtosecond oscillators. One femtosecond oscillator has a repetition frequency of 1G+Δf Hz, which is the pump pulse; the other has a repetition frequency of 1G Hz, which provides the time difference between the pump pulse and the probe pulse, and the time delay varies periodically with the scanning cycle. The period can be given by 1/Δf. This system abandons the mechanical delay line necessary for the traditional THz-TDS system and uses double-photon detector to generate trigger signal. When the frequency difference between the two femtosecond laser oscillators is 1 kHz, a THz spectrum can be detected in only 1 ms, and a THz signal with a dynamic range of 21 dB and a spectral resolution of 5 GHz can be obtained in 10.3 s. Hence it can be characterized by fast detection speed and high resolution. It has incomparable advantages over the traditional THz-TDS system in the application environment that requires rapid measurement.
Study on thickness consistency of primary reflection laser screen
CHU Wenbo, ZHAO Donge, ZHANG Bin, CHEN Yuxuan
2019, 40(2): 233-240. doi: 10.5768/JAO201940.0201009
In the primary reflection type laser screen velocity measuring technique, the scattering angle of the laser beam generated by the semiconductor laser source makes the thickness of the emergent optic screen inconsistent, and the residual divergence angle of the reflected optic screen generated by the primary reflective screen makes the thickness of the reflected optic screen inconsistent, the two aspects from which lead to the problem that the projectile passing through different positions of the optic screen to trigger the response time of the optic screen inconsistent. According to the geometrical optics principle, the mathematical model of the sagittal and meridional directions of the semiconductor laser was established, and the aspherical collimating lens groups with different surface figures were designed, the size of the exit spot was controlled within 1 mm and the divergence angles of the meridional and sagittal directions were 0.13 mrad and 0.46 mrad, respectively. After the exit beam was one-dimensionally expanded by the Powell lens, a fan-shaped exit light screen with a thickness of 1 mm and a uniformity of 85.7% was formed. And after the original reflection, the effective thickness of the reflected light curtain was effectively controlled to 1 mm with the slit aperture. Moreover, the Zemax software was used to simulate the projectile passing throuth the screen. When the projectile did not block the system laser screen, the detector received the original reflected light intensity of 1.54 mW; when the projectile blocked the system laser screen, the detector received the original reflected light intensity of 1.03 mW; when the projectile was close to the side edge of the exit laser screen (ie, 1 mm from the screen edge), the light intensity received by the projectile trigger detector respectively at 100 mm, 300 mm, and 500 mm from the light source was all 1.54 mW. Obviously, there is no change in light intensity relative to the absence of the projectile blocking laser screen, which proves that the effective detectable optic screen thickness of the system is consistent and 1 mm. This result indicates that the research scheme is feasible.
Study on monochromatic holographic planar waveguide display system
WANG Longhui, WANG Gang, HUANG Liqiong, SHANG Tingting
2019, 40(2): 241-245. doi: 10.5768/JAO201940.0201010
A monochromatic holographic planar waveguide display system consisting of an out-coupled linear holographic grating and an in-coupled volume holographic grating was designed. The working principle of the system is that, first the monochromatic image light wave information emitted by the micro-display passes through the collimating lens, then the image light wave information is coupled from one end of the planar glass and coupled to the other end by in-coupled volume holographic grating and out-coupled linear grating, and finally enters the human eye at the exit pupil position. Its characteristics of the holographic grating were introduced. The angle of view of the holographic grating was deduced theoretically using the coupled wave theory and the K-vector closed legitimate, and the design method of the holographic grating was introduced at the same time. The method divides the laser into object light wave and reference light wave by beam splitter, and realizes interference on the holographic plate according to a certain angle of incidence. The final simulation results show that the system displays a field of view angle of 18°×14°, an exit pupil distance of 30mm, and the modulation transfer functions (MTFs) are all above 0.3 at 30lp/mm, which satisfies the requirements of the visual system and can be applied to a new generation of helmet display systems.
2019, 40(2): 209-209.
Oe Information Acquisition and Processing
Deformation detection system of fuel assembly based on underwater binocular vision
WANG Congzheng, HU Song, FENG Chang, GAO Chunming
2019, 40(2): 246-252. doi: 10.5768/JAO201940.0202001
The deformation state of fuel assembly is an important monitoring index during core operation. The deformation detection system of spent fuel assembly based on underwater binocular vision can not only obtain three-dimensional (3D) sizes of key parameters of spent fuel assembly, but also measure the overall outline of the assembly. Based on high temperature and high radiation characteristics of underwater large-scale target, an underwater binocular detection system based on 16 sets of camera units was developed. And the detailed design of its modules was given. By means of Harris feature point and regional grayscale cross correlation method, the fast stereo matching of binocular camera module with radiation noise was realized. According to the experiment results of simulated pool and nuclear power field, the local measurement accuracy of the system is better than 0.2 mm, and the global parameters satisfy the measurement accuracy of 0.5 mm. It can provide a powerful tool for the measurement of local deformation and bending parameters of underwater spent fuel assembly with high temperature and high radiation.
Maximum likelihood pose estimation using machine vision
QU Yepin, ZHANG Chaoran, LYU Yuhai
2019, 40(2): 253-258. doi: 10.5768/JAO201940.0202002
The existing pose estimation algorithms do not make any statistical assumptions on the sampled data, and lack the evaluation criteria. Aiming at this problem, based on the probability density function of the signal, we derived the general form of maximum likelihood pose estimation based on machine vision was and proved that the traditional iterative algorithm is equivalent to the maximum likelihood estimation using single imag ein the case of isotropic Gaussian noise.What's more, we derived the Cramér-Rao bound of pose estimation, which could be regarded as the variance low bound of any unbiased estimations. By the analysis of the simulation, the maximum likelihood method is much better than the traditional iterative method by using 10 pictures when noise power is greater than 5 dB, it proves that the performance of pose estimation can be improved by increasing the number of images.
Matching method of large array CCD aerial images based on local hashing learning
CHEN Suting, GUO Ziye, ZHANG Yanyan
2019, 40(2): 259-264. doi: 10.5768/JAO201940.0202003
In order to realize the fast and accurate matching of large array charge coupled-device (CDD) aerial images, a local multi-feature hashing (LMFH) method is proposed. Firstly, the prediction area is constructed according to the course overlap rate, and the feature points detected in the area are described by multi-feature. Then, the hash functions are learned by tens of thousands of existing aerial images. Finally, the high-dimensional feature description vectors are mapped to compact binary hash codes by the learned hash functions. Fast hashing matching is achieved according to the Hamming distance in the Hamming space. Experiments show that compared to the classical speeded up robust features (SURF) algorithm, accuracy is improved about 10%, meanwhile, the matching time is decreased 0.2s. The proposed LMFH algorithm for aerial images matching is much more efficient.
Fast phase unwrapping algorithm for 3D measurement
WANG Lin, HAN Xu, FU Yanjun, HUANG Chunzhi, SHI Yaoqun
2019, 40(2): 271-277. doi: 10.5768/JAO201940.0202005
Reducing the number of fringe patterns for fringe projection profilometry (FPP) has been a hot topic in the field. The traditional temporal phase unwrapping algorithm generally requires additional fringe information to determine the fringe order, which leads to the excessive number of fringe patterns.A fast phase unwrapping algorithm for three-dimensional (3D) measurement is proposed. Only N-step standard phase-shifting sinusoidal fringe patterns are needed to calculate the absolute phase. Firstly, the standard phase-shifting algorithm is used to calculate the wrapped phase and the mask to eliminate the background. Then, the wrapped phase and mask are used to solve the fringe level according to the connected component labeling theorem, and then the absolute phase is obtained. The proposed method needs a minimum of three fringe patterns to complete the 3D measurement, and the data processing speed is fast. Computer simulation and experimental results verify the effectiveness and robustness of the proposed method.
Optical Metrology and Measurement
Seawater chemical oxygen demand optical detection method based on Raman spectroscopy
WU Guoqing, ZHAO Weiguang
2019, 40(2): 278-283. doi: 10.5768/JAO201940.0203001
The chemical oxygen demand (COD) of seawater directly determines the degree of pollution of seawater water quality. The fluorescence interference in the traditional ultraviolet(UV)-visible light detection is relatively large, and the infrared absorption peak of water molecules is seriously affected when the chemical oxygen demand of seawater is detected by the near infrared light. A COD detection method for seawater based on Raman spectroscopy was proposed. The simulated seawater samples of different concentrations were used as the subjects to determine the characteristic Raman displacement of 981.6 cm-1. After pre-processing of Raman spectroscopy, by partial least square method, a regression model was established for the relative strength of Raman spectrum and the seawater COD values measured by potassium permanganate method. The experimental results show that the correlation coefficient between the training set and the prediction set reaches 0.99, the determination coefficient of the verification set reaches 0.990 9, and the predicted mean square root error is 0.79 mg/L.
Research on high deterministic removal characteristics of fused quartz using RF focused ion beam source
XI Yingxue, LIU Weiguo, MA Zhanpeng, ZHANG Jin, ZHOU Shun
2019, 40(2): 284-290. doi: 10.5768/JAO201940.0203002
The characterization of the deterministic material removal plays an important role in the ion-beam figuring (IBF) polishing process, which is used to predict the material removal and help to determine the dwell time needed at different positions of the workpiece. The ion beam etching characteristics of fused quartz optical components were studied by radio frequency(RF) ion source, the precise removal function was calculated and obtained by using ZYGO interferometer, and the influences of the plasma source operational parameters such as work gas mass flow rate, screen voltage, incidence angle of ion beam and work distance on the material removal function of fused quarts were investigated. Furthermore, the relative change rates of the material peak removal rate, the full-width-at-half-maximum (FWHM) of peak and the material volume removal rate were measured and calculated when individual work parameter was perturbed. The experiment results show that the variation of removal functions varies slightly with the gas mass flow rate under the same work vacuum pressure. It is found that the relative errors of the removal function's peak removal efficiency, the FWHM and the volume removal efficiency can all controlled in 5% when the screen voltage fluctuation is ±5 V, the incidence angle deviation of ion beam is ±1° and the work distance deviation is ±0.5 mm, respectively. Hence the removal function of IBF for fused quartz by using RF focusing ion source has better certainty and stability.
Research on femto-second laser pulse width and pulse waveform measurement technology
WU Lei, YIN Wanhong, YU Bin, DONG Zaitian, XUE Yuanyuan, CHEN Juan, YU Dongyu, WU Pei
2019, 40(2): 291-299. doi: 10.5768/JAO201940.0203003
Femto-second laser has an important application prospect in the fields of laser fusion, satellite precision ranging, laser micromachining, etc. And it is the main pump source of terahertz(THz) wave. The principles of the measurement methods of femto-second laser pulse width and pulse waveform are introduced. The advantages and disadvantages of the measurement methods of autocorrrelation (AC), frequency-resolved optical gating (FROG), and spectral phase interferometry for direct electric-field reconstruction (SPIDER) are presented. The AC is characterized by wide range of pulse width measurement and compact structure, however it does not have the ability of pulse waveform measurement. The SPIDER requires high quality of input laser beam and it is not suitable for fast measurement of laser pulse width in a large range. In order to meet the test requirements of ultra-short laser pulse width and pulse waveform in the range of 10 fs to 5 ps, a femto-second laser pulse width and pulse waveform measurement device was developed by using AC and FROG methods, and the time resolution is better than 2 fs.
Application research of FBG sensors used in cavity explosion for pressure measurement
ZHANG Jijun, ZHANG Dongliang, LI Liang, ZHANG Baoguo, ZHAO Jianwei, TAO Jun
2019, 40(2): 300-305. doi: 10.5768/JAO201940.0203004
The fiber Bragg grating(FBG) sensor has extensive application prospects in the field of explosion impact testing for its merits like high sensitivity, wide measurement range, anti-electromagnetic interference capability, high temperature resistance and so on. An anti-impact FBG pressure sensor was designed for the performance requirements of pressure sensor in the process of cavity explosion pressure change. The sensor used a flat diaphragm as the bearing surface, and used the deflection under uniform pressure to stretch the FBG so as to generate displacement. The mechanical model of the sensor was theoretically calculated and the finite element simulation was carried out. Result shows that the error between theoretical analysis and numerical simulation is less than 2%. And the sensor was calibrated using a standard pressure source with a final pressure sensitivity of 545.187 kPa/nm and a linearity correlation of 99.998%. In addition, according to the protection requirements of the cavity explosion site, an effective anti-explosion protection device was designed, and the sensor was successfully used for the measurement of gas pressure change history after cavity explosion, which achieved good test results.
Optical Element and Fabrication
Metasurface fan-out diffractive optical elements
CHEN Kuixian, WANG Yu, HE Taotao, CUI Yuan, TAO Jin, LI Zile, ZHENG Guoxing
2019, 40(2): 306-310. doi: 10.5768/JAO201940.0205001
Here we report the design and realization of dielectric fan-out diffractive optical elements (DOEs) operating in visible range and with nanobrick depth-width-ratio as low as 1.5. The metasurface-based fan-out DOEs realized here, when illuminated by an incident beam with 633 nm wavelength, the uniform 4×4 spot arrays with an extending angle of 32°×32° can be obtained in the far field. Experimental results agree well with the theoretical analysis and numerical simulation conclusions. Because of these advantages of the single-step nonstructural fabrication procedures, continuous and accurate phase manipulation, and strong polarization conversion, the metasurface-based fan-out DOEs could be utilized for various applications such as optical sensing, lidar, laser machining and so on.
Biomimetic hybrid fisheye/compound eye imaging system with wide view and high resolution
LU Wenwen, CHEN Shanyong, ZHAI Dede, XIONG Yupeng
2019, 40(2): 311-315. doi: 10.5768/JAO201940.0205002
Based on the multiscale imaging theory, a biomimetic hybrid fisheye/compound eye imaging system is utilized for wide view and high resolution sensing. The objective is a relatively large-aperture ball lens collecting the wide-angle target light and imaging it onto an intermediate image surface which is spherical and concentric with the ball lens. The intermediate images are then corrected for aberration and imaged onto the detector array by a small-diameter lens group array which work as the eyepiece and are spherically symmetric about the center of the ball lens. A comparison of imaging performance is presented between the system using concentric double ball lenses and the system using single ball lens as the objective, respectively. The latter has even better imaging performance and avoids the problems of tolerancing, mechanical and thermal instability of the cemented ball lenses. The designed full field of view is over 100° while the angular resolution is higher than 10″and the distortion is less than 5% in the full field. The system has a large depth of field. Targets from 300 m away to infinite can be simultaneously imaged without focus adjustment. It can be widely used in the field of surveillance.
Design on projection objective of portable projector
WANG Kang, DUAN Jie, ZHOU Jianhong, WANG Chen, FU Yuegang
2019, 40(2): 316-322. doi: 10.5768/JAO201940.0205003
In view of the shortcomings of current projectors such as large light source power consumption, poor light projection stability and large system structure, using Zemax software, a large field of view(FOV), short focal length and compact projection system for portable projectors was designed. After optimization, the design structure was finally obtained with good imaging quality. At the spatial frequency of 80 lp/mm, the central FOV modulation transfer function(MTF) is ≥ 0.7, the 0.8 FOV MTF is ≥ 0.6, the edge FOV MTF is≥ 0.48, and the distortion is less than 3%, which can satisfy the design indicators given. Moreover, the energy concentration is greater than 85% in the specified and required pixel size range, the overall illumination curve is higher than 90% within 0.8 FOV, the energy concentration is high, and the illumination uniformity is good, which can be well matched with the portable projector for use. Key words: short-focus; Zemax; wide field; projection optics
Design of rectangular composite paraboloid three-dimensional two-way lighting and energy-saving reflective cup
LIN Wenshuo, SHI Mengjing, BAI Yin, LYU Shaozhen, LU Mei
2019, 40(2): 323-333. doi: 10.5768/JAO201940.0205004
A new concept of optical design with two-way multi-function for making full use of the lamp space was proposed.The rectangular composite paraboloid was constructed through combining the light emitting diode (LED) and the compound parabolic concentrator (CPC) based on the conservation of optical expansion and the principles of optical path reversibility and the edge ray.According to the latest performance requirements of reading and writing desk lamp in China, GB/T 9473-2017, the orthogonal experiment was designed based on three factors:the half width of light outlet, the irradiation height of desk lamp, and the length ratio of truncated cup body. It was determined that the most suitable rectangular compound parabolic parameters were as follows: the half width of light outlet of 50 mm, the max half angle of the inlet light of 47.73°, the truncated cup body length of 36 mm. Results show that in terms of illumination, the rectangular compound paraboloid satisfies the requirements for illumination and uniformity of national standard A and AA; in terms of low light collection, with the aid of the rectangular composite parabolic concentrator, the illumination of the solar chip position is 1.25 times higher than that without concentrator; in concentrating mode, the photovoltaic conversion efficiency of the solar chip is 1.66 times of that in non-concentrating mode. This is a complement to the current solar energy collection methods in the market, which are non-concentrated mode.
Optical system design of four-channel low light level polarization imaging
JIA Chunhui, GAO Ming, YANG Shuning
2019, 40(2): 334-341. doi: 10.5768/JAO201940.0205005
In order to improve the quality of low-light-level(LLL) imaging and achieve the requirement for real-time imaging for dynamic targets or changing scenes, a LLL polarization real-time imaging optical system was designed based on the polarization imaging principle and the division of aperture technique. To achieve simultaneously polarization imaging, the optical system uses an array of common-caliber four-channel configuration. This structure divides four polarization states to be measured into four independent imaging channels, and four-quadrant segmentation imaging is performed on the target surface of the detector through a sub-aperture imaging group set. Each polarized channel obtains an intensity image with different polarization states by placing polarizing plates with different polarization states. The focal length of the optical system is 100 mm, the system whole F number is 1.2, the operating wavelength is 0.4 μm~0.85 μm, the minimum working illumination is 1×10-3 lx, and the 1 080 pixel full high-definition (HD image) can be outputted. The total optical length of the system is 167.5 mm, and the modulation transfer function (MTF) value of the single-channel is higher than 0.57 at 40 lp/mm in full field of view.
Fiber Sensing and Optical Communication
Fabrication and optical properties analyses of thin film optical tapered grating
GE Shaobo, LIU Weiguo, ZHOU Shun, LI Shijie, YANG Pengfei
2019, 40(2): 342-348. doi: 10.5768/JAO201940.0208001
In order to introduce a continuous contoured microstructure into the optical thin film, the refraction, diffraction of the microstructures and the interference of the thin film were comprehensively utilized, and the preparation process of the thin film optical microstructure was proposed. The thin film optical tapered grating with anti-reflection characteristics in visible light was designed based on the finite difference time domain method. A tapered grating having a height of 1.6 μm and a period of 4.1 μm was prepared in the SiNx film by single point diamond turning technology, combined with nanoimprint lithography and inductively coupled plasma etching, In the visible band, the SiNx thin film optical tapered grating had an average reflectance of 5.7%, and the experimental results of the reflectance were highly consistent with the simulation results; when the incident angle was within 30°, the anti-reflection characteristic of the thin-film optical tapered grating exhibited an insensitivity to the incident angle of the light waves. It is indicated that the preparation process breaks through the material limitations of the single point diamond turning technology, it can extend the direct formation process of the continuous contour microstructure into the dielectric thin film, and can achieve the anti-reflection of wide spectrum and wide angle.
Research and application of spectrum characteristics of single phase-shifted fiber Bragg grating
YANG Siyu, WAN Shengpeng, WANG Haoyu, SONG Zaobiao, HE Jiaxiang
2019, 40(2): 349-355. doi: 10.5768/JAO201940.0208002
Narrow linewidth fiber lasers have lots of applications in fiber communication, fiber sensors, coherent detection and combination because of its narrow linewidth and low noise. According to the transfer matrix method, we simulated the transmission spectrum of single phase-shifted fiber grating by Matlab, analyzed the transmission spectrum of single phase-shifted fiber grating with the different phase-shifted magnitudes, locations, fiber grating lengths and the different refractive indicators of the core, and got the main factors affecting the transmittance, linewidth and position of the phase-shifted peak.Furthermore, we proposed a scheme of tunable narrow linewidth erbium-doped fiber laser using a phase-shifted fiber grating with a π phase-shifted and a location of phase-shifted at the midpoint as the filter window.
Method for detecting far-field spot uniformity of optical fiber output
LIU Bohan, LAI Min, XIAO Shaorong
2019, 40(2): 356-362. doi: 10.5768/JAO201940.0208003
In order to detect the uniformity of the optical output light spot, a method based on imaging method for detecting the uniformity of the optical fiber spot using the regional averaging method was proposed. Firstly, the digital camera was used to acquire the light spot from the experimental device. Then, the regional averaging method was used to detect the uniformity of the image, and the uniformities of the whole area and each small area were calculated to get the area with the best image uniformity. At the same time, the concept of uniform depth was introduced as a basis for judging the uniformity of the light source. The results show that the uniformity of the spot after adjustment reaches more than 99.7%. Through the comparison of the light spot obtained by the experimental apparatus before and after adjustment, and the comparing with the theoretical calculation of the optical fiber output spot distribution, the validity of the method can be verified.
2019, 40(2)