2020 Vol. 41, No. 3

2020, 41(3): 1-6.
Optical design of VIS/MWIR dual-band common-aperture system
HAN Peixian, REN Ge, LIU Yong, GUO Junli, ZHOU Jianwei, CUI Zhangang
2020, 41(3): 435-440. doi: 10.5768/JAO202041.0301001
In order to improve the ability of target detection and recognition of the photoelectric detection equipment, a set of VIS/MWIR dual-band common-aperture optical system was designed. Based on the practical engineering experience, an optical design method with segmented design and combinatorial optimization was summarized, and the design process of the initial structure for the dual-band common-aperture optical system was reconstructed by reasonably distributing the focal power and selecting the appropriate initial structure. In addition, combined with CodeV and TracePro soft, the narcissus phenomenon of the refrigeration mid-wave infrared detection system was quantized, and the validity of the analysis conclusion was verified by the field test imaging. In the dual-band common-aperture optical system, the maximum field of view is 1.25°, and the distortion is less than 0.1%, which can work at ambient temperature −30℃~50℃. The 100% cold shield efficiency is realized by the mid-wave infrared detection system, and the switching of the size of the field of view is realized by the visible light detection system. The dual-band optical system has the functions of focusing and dimming, which shows good imaging quality, good processability, small assembly difficulty, and strong engineering implementability.
Absorptance measurement on Nb2O5 coating with lock-in thermography method
LIU Feng, GALLAIS Laurent
2020, 41(3): 441-446. doi: 10.5768/JAO202041.0301002
The absorptance of the optical coating was quantitatively measured by the lock-in thermography method. The periodically modulated laser intensity was absorbed by the coatings to be tested, and a thermal wave was formed on the coatings surface. The thermal distribution signal recorded by the infrared camera was processed by the lock-in method to obtain the thermal image with improved SNR. The standard absorption samples were used to calibrate the system to obtain the quantitative relations between the photothermal signal amplitude and the samples absorptance, then the samples to be tested were measured under the same experimental conditions, and the absolute absorptance could be obtained by the direct calculation of the photothermal signal. The experimental study is carried out at the wavelength of 1 060 nm, the absorptance of the Nb2O5 coating with different thickness was measured, and the measured absorptance can reach to 80 ppm.
Research on diffraction effect of primary mirror in segmented telescope
ZHANG Long, WANG Xiaokun, CHENG Qiang, HU Haixiang
2020, 41(3): 447-454. doi: 10.5768/JAO202041.0301003
The design of the segmented primary mirror makes an idea of the extremely large aperture telescope a reality. In order to study the imaging performance of the segmented telescope, the effect of the segmented primary mirror configuration, translation error, and tilt error on diffraction effect was precisely analyzed and quantified. Based on the imaging principle of the segmented optical system, the pupil models of the segmented primary mirror were established based on the homogeneous coordinate transformation. And the effect of the segmented primary mirror configuration on the diffraction effect was simulated and analyzed. The analysis results show that for the segmented primary mirrors with different configurations, the diffraction effect is affected by the fill factor and the aperture interval of the segmented primary mirror, the higher the fill factor, the smaller the aperture interval, and the better the system imaging quality. Taking the typical segmented primary mirror configuration as an example, the effect of the translation error and tilt error of the single sub-mirror and the overall translation error and tilt error of the segmented primary mirror on diffraction effect was simulated and analyzed, respectively. The analysis results show that for the single sub-mirror, the effect of the translation error on far-field diffraction is periodic. And for the overall segmented primary mirror, the Strehl ratio is higher than 0.95, when the root mean square of the sub-mirror piston error is less than 0.039λ, or the root mean square of the sub-mirror tip-tilt error is less than 0.036λ. The analysis results provide the basis for the imaging performance analysis of the segmented telescope, the configuration design of the primary mirror, and the detection and adjustment of the translation error and tilt error.
Analysis and suppression of stray light in miniaturized panoramic system
LI Yuheng, LIU Zhiying, HUANG Yunhan, WANG Xu
2020, 41(3): 455-461. doi: 10.5768/JAO202041.0301004
Due to the complex structure of the head unit for the panoramic ring optical system, the internal optical path is reflected and refracted for many times, which results in a serious condition of the stray light. Therefore, in the design process of the panoramic ring optical system, the analysis of the stray light is very important. The form of the stray light of the head unit for the panoramic ring optical system was analyzed, and the mathematical model of the stray light elimination was established for the stray light which was not reflected by the head unit of the panoramic ring optical system. On this basis, the panoramic ring optical system was optimally designed. The stray light reflected by the head unit cementing surface of the panoramic ring optical system was suppressed by a meniscus adhesive mirror with convex image surface, and modeled as well as simulated by the ASAP software. The simulation results show that the stray light energy is reduced by 90%, which proves that the adopted form and the mathematical model of the stray light elimination can effectively suppress the generation of the stray light.
Denoising method for spectrum of spatial heterodyne spectrometer
WANG Xinqiang, ZHANG Shiyi, XIONG Wei, YE Song, WANG Fangyuan, LI Shu, LI Li
2020, 41(3): 462-468. doi: 10.5768/JAO202041.0301005
The spatial heterodyne spectrometer is a new ultra-high resolution spectrometer, which can be used for the atmospheric monitoring, satellite remote sensing and other fields. In order to reduce the noise in the spatial heterodyne spectral signal, a denoising method based on lifting wavelet transform combined with median filter was proposed. The two-factor threshold function and hierarchical threshold selection were incorporated by the improved lifting wavelet transform. Compared with the soft and hard thresholds of the wavelet transform, the spatial heterodyne spectrum could be extracted, the peak width could be reduced, and the important detail features could be preserved by the proposed algorithm, which had superior denoising effect than the wavelet transform. Finally, the two quantitative indexes of SNR and mean square error were used to measure the effect of the proposed algorithm. The experimental results show that, compared with the soft threshold method, the signal-to-noise ratio of the algorithm for the xenon lamp and the integrating sphere is increased by 24.6% and 31%, respectively, and the mean square error is reduced by 43.2% and 51.5%, respectively. Compared with the hard threshold method, the signal-to-noise ratio is increased by 21.5% and 30.6%, respectively, and the mean square error is reduced by 40.2% and 51.2% respectively. Therefore, the algorithm is feasible in the spatial heterodyne spectral noise reduction.
Design of narrow beam illumination optical system based on LD excitation phosphor white light source
GUO Jintao, XIONG Deping, WEN Kunhua, HE Miao, ZHANG Zhiqing, XIA Zhifeng, XU Yiqin
2020, 41(3): 469-476. doi: 10.5768/JAO202041.0301006
The technology of the blue light semiconductor laser excitation phosphor to produce the white light source is developing rapidly. However, due to the large difference of the light field distribution in the fast axis and slow axis direction of the high-power blue light semiconductor laser, the overall optical properties of the laser illumination are still poor, which is difficult to achieve the large-scale application. Aiming at this problem, a high-quality laser illumination optical system was designed based on the Monte Carlo ray tracing theory. The collimation regulation of the laser beam was carried out, the uniform light spot was shaped, and the fluorescent sheet was designed, so that the components of overall light source modules obtained the optimal integration, and the narrow beam laser illumination was finally realized. The simulation results show that the light collection rate of the laser light source reaches to 98.3%, the ununiformity of the laser spot is 1.7%, the uniformity of the white light is 98%, and the light spot is the square narrow beam white light spot with an exit collimation angle of 1.6°.
Analysis of focal length error in torsion angle measurement system
YANG Wenchang, WANG Zhiqian, SONG Zhuoda, DU Wen, LI Qinwen
2020, 41(3): 477-481. doi: 10.5768/JAO202041.0301007
Aiming at the torsional deformation scheme of Moiré fringe measurement, the influence of double- grating on the measurement accuracy of torsion angle in the optical system with focal length error was analyzed. Based on the traditional Moiré fringe measurement torsion angle theory formula, the scaling effect of focal length on the grating image was introduced, and the torsion angle measurement model with focal length factor was derived. According to the derived model, as the focal length difference of the optical system increases, the corresponding torsion angle also changes greatly. Especially the change at small angles (1°~3°) is particularly obvious, which ultimately affectes the measurement accuracy of the torsional deformation. In the designed experiment, the theory proposed was verified by using two optical systems with known focal lengths to analyze the torsion angle accuracy by collecting the Moiré fringe image.
Light field refocusing analysis of different interpolation algorithms
CHANG Qing, ZHAO Shuangming
2020, 41(3): 482-489. doi: 10.5768/JAO202041.0302001
The light field data refocusing includes spatial domain refocusing and frequency domain refocusing. In the process of the refocusing, the interpolation calculation is needed, the refocusing precision is closely related to the interpolation precision, and the computational efficiency can be affected by the complexity of the interpolation algorithm. In the actual large amount of the image processing, the method with the highest computational efficiency is selected under the premise that the refocusing effect satisfies the accuracy requirement, and wherein the interpolation accuracy has a much greater influence on the frequency domain than the spatial domain. The principle of the spatial domain refocusing and the frequency domain refocusing, as well as the traditional three interpolation methods and the sinc function interpolation method were introduced. Different interpolation methods were used to experiment this two refocusing methods to compare their refocusing effect and calculate their efficiency. The experimental results show that in order to meet the requirement of the computational efficiency in actual applications, the linear interpolation method is the best method to optimize the spatial domain refocusing in the case of meeting the accuracy requirement, and the sinc interpolation with the sampling radius of 2 is optimal in the frequency domain. When the same image is refocused for multiple times, the frequency domain method is superior to the spatial domain method.
Depth estimation based on adaptive pixel-level attention model
CHEN Yuru, ZHAO Haitao
2020, 41(3): 490-499. doi: 10.5768/JAO202041.0302002
Depth estimation is a traditional computer vision task that plays a vital role in understanding the geometry of the 3D scenes. The difficulty of the depth estimation task based on monocular images was how to extract the context information of the long-range dependence in image features, therefore an adaptive context aggregation network (ACANet) was proposed to solve this problem. The ACANet was based on the supervised self-attention (SSA) model, which could adaptively learn the similarities with task traits between arbitrary pixels to simulate the continuous context information, and the attention weight distribution of the model learning was used to aggregate and extract the image features. Firstly, the monocular depth estimation task was designed as a multi-class classification problem at the pixel level. Then the attention loss function was designed to reduce the semantic inconsistency of the RGB image and the depth map, and the features indexed by positions were globally pooled by the generated pixel-level attention weights. Finally, a soft ordinal inference (SOI) algorithm was proposed, which fully utilized the predicted confidence of network to transform the discrete depth labels into the smooth continuous depth maps, and the accuracy was improved (rmse decreased by 3%). The experimental results on the public benchmark data set NYU Depth V2 of the monocular depth estimation show that, the rmse index is 0.490, and the threshold index is 82.8%. The better results are obtained, which prove the superiority of the proposed algorithm.
Multi-focus image fusion method based on improved VGG network
CHEN Qingjiang, WANG Zebai, CHAI Yuzhou
2020, 41(3): 500-507. doi: 10.5768/JAO202041.0302003
In order to better retain the original image information and improve the image fusion performance, an improved fusion algorithm combining visual geometry group(VGG) convolutional neural network with edge pixel statistical features was proposed. Firstly, this algorithm divided the complete image into image blocks, preprocessed the image blocks to obtain a higher image classification accuracy of 0.985 or more, and used the improved VGG convolutional neural network to accelerate the convergence of the model. When the image blocks were input into the network, the weight matrix of binary classification could be preliminarily obtained. Secondly, in the high-frequency detail part, the clear blur modules of left-focus image and right-focus image were respectively subjected to blurring processing, and the weights matrix with obvious boundaries was obtained by the threshold segmentation based on the statistical feature between the pixel points. Finally, combined with the two-step weight matrix, the fusion strategy of weighted sum was used to obtain the clear focus image. In order to illustrate the effectiveness of the algorithm, the experimental part shows the objective evaluation of its fusion subjective visual effect diagram and information entropy, which is outstanding compared with other algorithms and can better retain the information of the original image.
Self-adaptive bridge bare rebar detection algorithm based on local image segmentation and multi-feature filtering
HE Fuqiang, LUO Hong, YAO Xuelian, PING An
2020, 41(3): 508-515. doi: 10.5768/JAO202041.0302004
Due to the interference of the uneven illumination and the complex background, the traditional threshold segmentation methods are difficult to effectively separate the bare rebar from the background. An adaptive bridge bare rebar detection algorithm based on local image segmentation and multi-feature filtering was proposed. Firstly, the gray value of the gray image was needed to project, and the wave trough and its coordinates formed by the bare rebar on the projection were found out. Secondly, with the wave trough coordinates as the center, the segmentation range was set to divide the rows and columns of the gray image, and the merged gray image was segmented by the local threshold. Finally, the extraction of the bare rebar feature was realized based on the multi-feature filtering, and the proposed algorithm was used to verify 7 kinds of common bare rebars. The experimental results show that the average error rate, the missing rate and the relative error of the bare rebar length with manual measurement are 5.15%, 3.89% and 3.74%, respectively, which meet the criterion of the highway disease evaluation and realize the adaptive recognition of the bare rebar under complex environment.
Roll coating thickness image detection based on ant colony algorithm
BAO Nengsheng, FANG Haitao
2020, 41(3): 516-522. doi: 10.5768/JAO202041.0302005
Aiming at the problems of low efficiency and accuracy for roll coating thickness detection, a machine vision detection method based on heuristic ant colony algorithm was proposed. The principle of Canny operator was used to extract the edge information and obtain the prior knowledge of edge points. Then an improved edge tracking model of ant colony algorithm was established, which realized the guidance of pheromone and heuristic information to ants, avoided the distribution and walking of ants in non-edge areas and solved the problem of coordinated randomicity and positive feedback in traditional ant colony algorithm. This improved ant colony algorithm based on machine vision was used in the measurement experiment. Compared with the mechanism modeling method, the maximum error is 5.74%, and the average error is 4.04%, which meet the actual production needs.
Generation of sparse spectrum turbulence phase screen by partition allocation method
ZHANG Xiaoqi, NI Xiaolong, LIU Zhi, CONG Minghui, ZHANG Jie
2020, 41(3): 523-530. doi: 10.5768/JAO202041.0302006
In order to better study the propagation characteristics of the beam in atmospheric turbulence, a simulation method of the turbulence phase screen based on the sparse spectrum model was proposed, and the gray image, structure function and beam drifting distance of the generated phase screen were analyzed. Firstly, the mathematical method was used to analyze the direction, size and amplitude of the light wave, and the sparse spectrum phase screen was obtained. Then, under the different coherence radius, it was compared with the phase screen gray image generated by the power spectrum inversion method, and the fitting degree of the structure function and the spot position under the sparse spectrum model was analyzed. The simulation and experimental test results show that the average error of the experimental structure function is 6.1%. The phase screen detail information is more abundant under the simulation method, and the root mean square error of the atmospheric turbulence spot centroid is 1.013×10-7 m, which has the advantages of high precision, fast running speed, long simulative period, etc., and can better simulate the real atmospheric turbulence.
Research on weld defect image classification based on convolutional neural network
GU Jing, ZHANG Keshuai, ZHU Yiman
2020, 41(3): 531-537. doi: 10.5768/JAO202041.0302007
In order to effectively classify the weld defects and judge the grade of the welding quality, a multi-scale squeeze-and-excitation network model (SINet) was proposed to improve the traditional convolutional neural network. Combined 4 groups of 3×3 convolutional modules in series with Inception module and squeeze-and-excitation block (SE block). By means of the multi-scale squeeze-and-excitation module (SI module), the multi-scale fusion and the feature re-calibration were carried out of the features in convolutional layer to improve the classification accuracy, and the global average pooling layer was used instead of the fully connected layer to reduce the model parameters. In addition, considering the influence of the unbalance in the number of weld defects on the accuracy, a deep convolutional adversarial generation network (DCGAN) method was used to balance the data set, and the validity of the model was verified on the data set. Compared with the traditional convolutional neural network, this model has good performance with an accuracy rate on the test of 96.77%, and the number of the model parameters is also greatly reduced. The results show that this method can effectively classify the weld defect images.
Image detection method for surface defects of brake pads
HAN Zhiwei, GAO Meifeng
2020, 41(3): 538-547. doi: 10.5768/JAO202041.0302008
In order to deal with the different surface textures and various types of automotive brake pads, an image detection method for surface defects of brake pads based on machine vision was proposed, which combined the gray co-occurrence matrix and the density clustering. Firstly, the friction surface of the brake pad was extracted. Then the construction factor selection of the gray co-occurrence matrix was determined, and the linear correlation was used to select the characteristic parameters. Each friction surface was divided into several small windows, and the eigenvalue of each small window was calculated to construct the feature data sets. The cluster analysis was carried out by the adaptive density clustering algorithm, so as to further determine whether there existed a defect area or not. Based on the statistical analysis of the test results of 58 brake pad samples of different models, the experiment shows that the method has a high detection accuracy with a false detection rate of 8% and a missed detection rate of 6%. Therefore, the method can better detect whether there are defects in the brake pad samples and has a wide range of applicability.
Measurement system of radiation sensitivity for UV image intensifier
WANG Shengyun, XIE Qi, SHI Jifang, SUN Yunan, YU Bing, KANG Dengkui
2020, 41(3): 548-552. doi: 10.5768/JAO202041.0303001
The ultraviolet (UV) image intensifier is the core device of the UV detection system, which is a kind of electric vacuum imaging device, and can transform and enhance the weak UV images into the optical images that can be detected by eyes. The development and application of the UV image intensifier is an important orientation of the low-light-level night vision technology. The radiant sensitivity is a key parameter to evaluate the UV image intensifier, which directly determines the performance of the UV detection system. The measuring principle of the radiant sensitivity for UV image intensifier was introduced, and the measuring system was constructed by the UV radiation source, grating monochromator system, testing dark box, micro galvanometer, computer and measuring software. The radiant sensitivity of three UV image intensifier at wavelengths of 260 nm, 280 nm and 320 nm was measured, respectively, and the measurement uncertainty was analyzed. The spectral range of the radiant sensitivity measuring system is extended to 200 nm~400 nm by the establishment of the measuring system, which makes up for the deficiency of the existing system and has broad application prospects.
Visual inspection method of detecting flaws on optical glasses surface
ZHU Yudong, CHEN Yuxue
2020, 41(3): 553-558. doi: 10.5768/JAO202041.0303002
A computer visual inspection method for detecting flaws on optical glasses surface was introduced. This method mainly aimed at detecting flaws such as pockmark, scratch, burr, edge damage and so on. According to the principle that bright spots and bright bands generated by the diffuse reflection of flaws under the action of side light, the flaws detection device based on reflection detection method was developed, and the work cycle of the device was less than 5 s per piece. The blackbody was creatively used to form the dark background and enhance the contrast. In the visual inspection, the total area detection method was used to detect the pockmark and scratch of glasses surface, and the edge burr detection method was used to detect the burr and edge damage of glasses edge. In the experiment, 53 pieces of 10mm diameter optical glasses were tested and the accuracy reached 100%. In the end, the detection result based on the 310 000 pixel CCD was given. According to the result, the total number of flaws on OK glasses is ≤100 (pixel), and the maximum gray value is ≤80. The total number of flaws on pockmark and scratch glasses is between 200 and 600 (pixel), and the maximum gray value is ≤210. The total number of flaws on burr/edge damage glasses is ≤100 (pixel), and the maximum gray value is between 200~255. Thus it can be seen that, the total number of flaws on pockmark and scratch glasses is obviously higher than that of flaws on burr/edge damage and OK glasses.
Measurement method of axicon cone angle based on moire fringes of non-diffracting beam
YANG Liangen, LIU Fan, RAN Jingjing, ZHAI Zhongsheng
2020, 41(3): 559-564. doi: 10.5768/JAO202041.0303003
In order to accurately measure the cone angle of an axicon, according to the characteristic that the spacing of the non-diffracting beam concentric annulus did not change with the distance and the amplification characteristic of the moire fringes, a measurement method of the axicon cone angle based on moire fringes of the non-diffracting beam was proposed. When the non-diffracting beams were split and combined by the beam splitter, the moire fringes were formed. Translating the position of one of the beams on the image sensor to realize the change of the moire fringes number, and according to record the center distance under different moire fringes, the axicon cone angle was calculated. The axicon with a cone angle of 0.5° was used as the measured object. Compared with the CMM measurement results, the relative measurement error of the proposed method is approximately 0.54%, and the repeatability is 0.86″, which verify the feasibility of the proposed measurement method of axicon cone angle.
Research on multi-sensor combination method for estimating relative pose
LU Ye, MA Guolu, ZENG Guoying, XIAO Xingwei
2020, 41(3): 565-570. doi: 10.5768/JAO202041.0303004
Aiming at the problem of the view shielding and the small size of docking area, a multi-sensor combined pose measurement method was proposed. The profilometer and the laser displacement sensor arranged before and after the module were adapted to obtain the cloud data of the feature plane point on the module. In addition, the rotation of the nutation angle and the shifting deviation of the location were calculated by the plane fitting and the geometric space projection method, simultaneously combined with the horizontal angle information provided by inclinometer stick to the target to calculate the rotation deviation of the precession angle and the self-rotation angle. The automatic docking platform prototype was developed by this method, and the indirect measurement of the relative pose in docking area was realized. The experimental results show that the position and the pose measurement accuracy of the system is better than 40 μm and 0.02° respectively. And the measurement stability and the benefit are obviously improved compared with the manual measurement, which proves the effectiveness of the proposed method and meets the needs of high precision pose measurement between equipment modules.
Compound eye binocular vision ranging method based on target motion
GAO Wenjing, YANG Yuli, XING Qiang, XU Haili
2020, 41(3): 571-579. doi: 10.5768/JAO202041.0303005
The insect (mantis) compound eye realizes the stereo vision by using dynamic difference of the target, which has the characteristics of large field of view, simple calculation and high real-time performance, and is a new direction of the stereo vision research. In order to realize the application of compound eye stereo vision in robot vision navigation, according to the compound eye structure and the information processing mechanism, a target rapid detection and location method based on ring photoelectric sensor was proposed and studied. Firstly, a ring sensor based on 6° angle distribution of 60 photodiodes was built to form an ring bionic compound eye with 360° field of view. Secondly, a rapid detection model of the moving target azimuth based on optical flow principle was established. The Fourier fitting method was adapted to optimize the azimuth detection model, and the simple and rapid detection in the range of the large field of view of the moving target azimuth and the target distance was realized. The experimental results show that: 1) the real-time detection of the target azimuth at the motion velocity of 30 mm/s in the range of 375 mm can be realized, and the measurement error is within 2°; 2) based on the target azimuth detection model, the stereo vision ranging of the binocular array sensor in the range of 300 mm×375 mm field of view overlap with an average measurement error of 10 mm can be realized. The moving target azimuth detection model based on optical flow can be used to realize the dynamic real-time detection of the moving target spatial position, and has broad application prospects in the fields of motion detection and vision navigation.
Research on 3D measurement and reconstruction of high-precision profile of multi-frequency grating object
YU Zihao, LIU Jin, YANG Haima, LI Meiying, XU Wei, XU Bin
2020, 41(3): 580-585. doi: 10.5768/JAO202041.0303006
In the current practical system, due to the existence of noise, the full-field phase value cannot be obtained when the single-frequency grating is phase-resolved point by point, which leads to the low reconstruction accuracy of small objects with complex profiles. A multi-frequency grating projection method was proposed to realize the high-precision reconstruction of the objects with small volume and complex morphology. The system algorithm decomposed the multi-frequency grating based on the improved four-step phase-shifting method which changed with time series. The multi-frequency grating decomposition separately expanded the phase of each frequency grating, and the grating decomposition of each frequency was carried out point by point. The discontinuous phase in the single-frequency grating due to noise could be repaired by fitting other frequency gratings, and a continuous phase in the whole field could be obtained. Experimental results show that the error range of single-frequency structured light is 0.1 mm~0.5 mm for measuring small and complex objects, while the precision of our method is 0.03 mm~0.05 mm, which can be improved by about 10 times.
Research on brightness adjustable integral sphere light source technology and its application
WANG Shaoshui, ZHAO Facai, SUN Quanshe
2020, 41(3): 586-590. doi: 10.5768/JAO202041.0303007
At present, the spectral radiation response function of the radiometer is calibrated by the irradiance standard lamp and diffuse reflector whiteboard, which cannot achieve linear calibration in a large dynamic range. A high-precision integral sphere light source with adjustable brightness was proposed. The output radiance was controlled by fixed and variable apertures, and the dynamic range reached 4 orders of magnitude. In addition,the spectral response function of the barrel-type radiometer was tested The experimental results show that the spectral response Function of barrel radiometer has good linear characteristics, high repeatability and the standard deviation of one-term coefficient is 2.78E-17.
Research on near-infrared polarization-independent metalens
PU Xinxin, ZHOU Shun, XIAO Xiangguo, ZHU Yechuan, CHENG Jin, LIU Weiguo
2020, 41(3): 591-596. doi: 10.5768/JAO202041.0305001
The metalens based on the micro-nano structure to achieve the focusing and imaging of the lightwave regulation is a front technology currently competing in international development. Aiming at the problems of near-infrared metalens polarization dependence, system complexity and low transmittance that had been reported, a near-infrared polarization-independent metalens was proposed. The low refractive index material SiO2 was used as the basement, the high refractive index material Si cylinder was used as the phase control unit, and the designed wavelength was 1.31 μm. The finite-difference time-domain method was used to analyze the lightwave regulation characteristics of the near-infrared metalens building unit, and the phase delay characteristic curve of the building unit was constructed. The influence law of the building unit period on the lightwave transmittance was discussed, the optimization design of the building unit was realized, and based on the wavefront reconstruction equation, the near-infrared polarization-independent metalens was designed. The numerical simulation results show that the phase delay and transmittance of the phase control unit are not only dependent on the radius and height of the Si cylinder, but also closely related to the unit period. Based on the analysis of the lightwave regulation characteristics for the building unit, the simulated focal length of the designed near-infrared polarization-independent metalens is 19 μm, which is in good agreement with the designed value, and the lens transmittance reaches 65%. The designed metalens is not only small in size, light in weight, but also is a plane lens. Therefore, it is easy to integrate the optical system, and it has broad application prospects in laser radar, laser night vision and other technologies.
Fresnel lens design for human posture estimation sensing
HE Yelin, ZHANG Jun
2020, 41(3): 597-602. doi: 10.5768/JAO202041.0305002
With the rise of virtual reality and somatosensory games, the human posture estimation has received increasing attention. The Fresnel optical microstructure lens in the human posture estimation sensing system based on pyroelectric infrared sensor was designed. After analyzing the theoretical formula of the cone even aspheric surface, the aspheric surface coefficients at all levels were calculated. Through simulation analysis, when the polymethyl methacrylate (PMMA) is selected as the material and the LHI968 detector with six sensitive element area of 2×1 mm2 as well as field angle of 100°×100° is adopted as the detector, the overall dimensions of the Fresnel lens is 28 mm×32 mm, the curvature radius of the front and back surface are 43.7 mm and 45.2 mm, respectively, and the center thickness is 0.6 mm. The final simulation results show that the light energy utilization rate of each detector is 96.70%, 94.8%, 96.95%, 97.75%, 90.65% and 90.15%, which can satisfy the response of the infrared light to different parts of the human body, so as to achieve the accurate estimation of the human posture.
Optical design of image telecentric lens for optical field multispectral camera
LIU Bo, LIU Jun, GAO Ming, LI Yang, ZHANG Wenxi
2020, 41(3): 603-610, 617. doi: 10.5768/JAO202041.0305003
The optical field multispectral imaging technique has the ability to simultaneously acquire the target two-dimensional spatial information and spectral information, and the classification and recognition of the target can be achieved by using the spectral information. In order to obtain the complete spectral information of the spatial target more quickly and conveniently, and realize the real record of the target surface spectral information, based on the principle of optical field multispectral imaging, the segmentation of the entrance pupil aperture for the main lens system was realized by adopting the array beam split of the spectral beam split filter, and an image telecentric lens optical system for optical field multispectral camera was designed. In this optical system, the wide band ranges from 400 nm~1 000 nm, the focal length is 240 mm, the F-number is 4, and the full field of view angle is 15.52°. The analysis results of the image quality evaluation and system tolerance show that the designed image telecentric lens for the optical field multispectral camera can satisfy the requirements of practical processing and normal use.
Research on analytical method of laser scanning projection files based on IGES
FAN Chengbo, ZHANG Mengmeng, LIU Jiqiang, CHEN Yuqing, LI Lijuan, HOU Maosheng
2020, 41(3): 611-617. doi: 10.5768/JAO202041.0305004
The laser scanning projector can realize the precise position projection of the wire frame contour for the components to be assembled, and can also greatly improve the problems of low precision and low efficiency caused by the traditional assembly method. In order to realize the 3D digital model laser projection in IGES format that can be read directly in the independently developed laser scanning projection system, the multi-feature image primitive extraction and the automatic files generation method were studied. In this method, the data features such as points, lines, and surfaces of the wire frame graphics to be projected were extracted and stored as the cellular in the .ply format file. The delay control of the numerical control switch and the control of the 2D vibrating mirror track were carried out by the .ply format file, which realized the more intelligent control of the laser scanning projection. The projection experiment of 12 IGES format image primitives verify that the proposed method can achieve the clear projection of all the image primitives, and the laser contour width is better than 0.3 mm. The assembly efficiency of the workshop and the assembly precision can be improved by using this new projection system.
Design of miniaturized fiber grating demodulation system and simulation evaluation of peak-detection algorithm
SUN Shanshan, YANG Xiong, WANG Haiyong, JIANG Yajun, YANG Dexing
2020, 41(3): 618-625. doi: 10.5768/JAO202041.0308001
In order to realize the real-time monitoring of the reflection spectrum signal in the fiber Bragg grating (FBG), the hardware system and the software architecture for demodulating the FBG signals were designed based on the all-solid-state spectrum module. The host computer software was programmed and embedded with different peak-detection algorithms, which could be applied to the calculation of the central wavelength under different noise environments to reduce the wavelength error caused by the algorithm. The software also included functions such as data acquisition, storage and playback. Taking Gaussian fitting peak-detection algorithm as an example, a method of simulation evaluation to peak-detection algorithm without hardware device was proposed, which improved the development efficiency of this kind of spectrum demodulation system. The simulation evaluation experiments were performed by using the ideal FBG reflection spectrum with different noise levels. The results show that the best peak-detection result can be obtained when the threshold is taken as twice the noise average amplitude, and the peak-detection errors are inversely proportional to the signal-to-noise ratio (SNR) of the collected data and the spectral peak width. The Gaussian fitting peak-detection algorithm is used to calculate the FBG reflection spectrum data actually collected by the hardware system, and the obtained accuracy of the system is 5.89 pm, the error from the simulation evaluation result is less than 1.7 pm, which proves the feasibility of the simulation evaluation.
Research on MIMO channel capacity for adaptive power allocation visible light
YANG Borui, ZHAO Li, LU Ying, ZHOU Yu
2020, 41(3): 626-630. doi: 10.5768/JAO202041.0308002
The multi-array light source layout is usually adopted by the visible light communication (VLC) system to give consideration to both illumination and communication functions. Therefore, the MIMO technology is required for the multi-antenna cooperative transmission to achieve the high-rate communication. However, the average power allocation is used to achieve the spatial multiplexing in the traditional MIMO system, which cannot fully reflect the advantages of the MIMO multi-antenna coordinated transmission. Based on the differences for the state of receiving and sending antenna channel in each group, a fast iterative water-filling algorithm with low computational complexity was designed, which could realize the allocation information on the basis of channel feature adaption and improve the channel capacity of the system. Finally, the simulation results show that under the same SNR, the channel capacity of the adaptive power allocation system with water-filling algorithm is about 1.25 bit/HZ higher than that of the equal power allocation system.
Micro-nano structure transfer method of optical fiber end face based on PDMS
HOU Tianfei, ZHAO Fusheng, WANG Bin, WANG Shuo, GAO Tianyuan
2020, 41(3): 631-636. doi: 10.5768/JAO202041.0308003
Micro-nano optical fiber sensor combines with micro-nano processing and optical fiber sensing technology, which has great significance in scientific research and industrilization potential. The preparation of the arbitrary complex three-dimensional (3D) structures cannot be achieved by the existing processing methods, thereby limiting the development of the micro-nano optical fiber sensor. A new processing method of micro-nano was proposed, which could achieve the preparation of the micro-nano structure on the polydimethylsiloxane (PDMS) thin films, then transferred the thin films and the micro-nano structure to the end face of the optical fiber, and the 3D micro-nano structure with artificial definition was achieved. The prepared samples are examined under the scanning electron microscope, and it is confirmed that the PDMS thin film and its 3D structure can be transferred to the end face of the optical fiber without loss. The proposed method has the characteristics of easy preparation, low cost and processing 3D micro-nano structure.
New photonic crystal fiber structure with high birefringence for liquid sensing
WU Rong, ZHANG Luyao, YAN Qingbo, LIU Zhen
2020, 41(3): 637-644. doi: 10.5768/JAO202041.0308004
A structure and design method of the photonic crystal fiber (PCF) for liquid sensing was proposed. The fiber core region of the hexagonal PCF was designed as two elliptical ventages, which were filled with water and ethanol, respectively, and then the propagation characteristics of two PCF structures were compared. The full vector finite element method (FEM) was adopted to numerically analyze the birefringence, relative sensitivity, confinement loss and nonlinear coefficient of the designed PCF structure. And the parameters of the optical fiber were optimized, meanwhile the parameters of the fiber core elliptical structure were adjusted. The results show that when the ellipticity is 0.6, the relative sensitivity of the PCF2 filled with ethanol can reach to 72.506 7% at the wavelength of 1.55 nm, and the confinement loss can deduce to the magnitude of 10−8. The designed model can be used in sensing as well as bio-sensing research and their applications.