2022 Vol. 43, No. 5

2022, 43(5): 1-6.
2022, 43(5): 1-1.
Development of aviation electro-optical reconnaissance technology
WANG Huilin, NING Fei, LIU Jilong
2022, 43(5): 825-832. doi: 10.5768/JAO202243.0509001
The aviation electro-optical reconnaissance has the advantages of strong concealment, good visibility and high resolution, and has always been an important means of military reconnaissance in various countries. According to the military mission requirements, the aviation electro-optical system could be classified into four categories: electro-optical targeting system, intelligence and reconnaissance surveillance system, infrared searching and tracking system and electro-optical missile warning and countermeasures system. The typical products were listed, and the characteristics and technical approaches were analyzed. The current status and development trend of domestic and foreign aviation electro-optical reconnaissance technology and equipment was analyzed in terms of optical implementation, stabilized platform evolution, line of sight stabilization, situation awareness, lightweight, multi-task coordination and open systems architecture (OSA).
Design and application of gyro redundant installation in airborne electro-optical system
LIU Dong, WANG Huilin, LEI Liang, JIANG Shizhou, WANG Guan, GONG Quancheng
2022, 43(5): 833-838. doi: 10.5768/JAO202243.0501001
The gyroscope is an important component for line-of-sight stabilization in electro-optical system. A redundant installation method of fiber optic gyroscope based on the electro-optical system was introduced. Under the premise that the number of redundant-installed gyroscope was determined, considering the installation space, volume, weight and cost of practical application of engineering, the redundant installation method of octagonal pyramid for 4 gyroscopes was designed. The precision and reliability of this redundant installation method were analyzed and simulated, and compared with the non-redundancy installation. This installation method could be used for redundant installation of gyroscope and magnetohydrodynamics angular rate sensor. The experimental results show that the standard deviation of noise is decreased about 25.3% and the reliability is improved about 1.75 times, which effectively solves the problem of insufficient gyroscope accuracy due to the limitation of installation space in an electro-optical system and improves the reliability. Meanwhile, the proposed method can be applied in the triaxial gyroscope stabilized electro-optical system, which has a certain guiding role for engineering application.
Design of large-aperture and wide-spectrum zoom lens
LUO Rui, LIANG Xiuling
2022, 43(5): 839-845. doi: 10.5768/JAO202243.0501002
In the process of high-voltage power line transportation, the corona discharge is easy to occur, which has potential safety hazards. Therefore, it is necessary to detect the corona discharge. Corona detection using solar blind ultraviolet (UV) lens is one of the detection methods. Based on the multiple configuration function of Zemax, a large-aperture and wide-spectrum zoom lens was designed to cooperate with the application of UV lens with the zoom range of 90 mm~165 mm, which could quickly and accurately find out the position of the damaged line in all-weather conditions when detecting the corona discharge signal. The four components and near-symmetrical structure were adopted by the proposed large-aperture and wide-spectrum zoom lens with the F number of 1.4, the zoom range of 30 mm~55 mm, the working spectral band of 400 nm~850 nm, the full field MTF≥0.4 at spatial frequency of 100 lp/mm, and the maximum distortion≤±3 %, all adopting standard spherical design, total length of the system is 110 mm, which is suitable for 0.847 cm (1/3 inch) CCD, and can better correct all kinds of aberrations as well as meet the basic processing requirements of each part.
Design of 20 mm~200 mm zoom objective lens for polarization imaging system
CHEN Xin, ZHEN Shenglai, FANG Jian, TAO Shanjing, YU Benli
2022, 43(5): 846-852. doi: 10.5768/JAO202243.0501003
The zoom objective lens is an important part of the polarization imaging system. At present, the zoom objective lens on the market is relatively expensive due to the use of more aspheric surfaces. In order to reduce the processing cost of the polarization imaging system zoom objective lens, a 20 mm~200 mm zoom objective lens for polarization imaging system was designed. By using positive group compensation method and Zemax to optimize the zoom system, the final system used only 7 spherical lenses to achieve good image quality. The modulation transfer function (MTF) is greater than 0.3 at 120 lp/mm, the distortion is less than 4%, and the cam curve of the system is smooth without breakpoints. The system tolerance analysis results show that the tolerance range is set as follows: the aperture tolerance of the lens surface is 2, the thickness tolerance of the lens or air center is ±0.02 mm, the inclination tolerance of the lens surface center is ±0.025°, the lens assembly and adjustment tolerance is ± 0.025 mm, and the lens refractive index deviation is 0.002. The tolerance setting conforms to the component processing and system assembly and adjustment process, which has a certain reference value to reduce the cost of polarization imaging system.
Qualitative analysis of reliability on servo stabilization platform of electro-optical system
ZHENG Fengzhu, NING Fei, WANG Huilin, WU Xiongxiong, WANG Guan, ZHAO Zhicao, ZHOU Yun, WANG Le
2022, 43(5): 853-858. doi: 10.5768/JAO202243.0501004
Taking the servo stabilization platform of two-axis and four-frame electro-optical system as the research object, the reliability of servo stabilization platform was qualitatively analyzed by using the failure mode, effects and criticality analysis (FMECA) and fuzzy analytic hierarchy process. After obtaining the critical failure modes and the list of reliability critical products of the servo stabilization platform, the fuzziness of human subjective judgment was fully considered, and the importance ranking of the impact of key products on reliability was further analyzed, which could be used as an importance reference for subsequent reliability design and distribution.
Filter method for pulse width modulation drive
LIU Changliang, DENG Yi, WANG Zicheng, PU Peipei, LI Chao, WU Yujing, ZHANG Jingyue
2022, 43(5): 859-863. doi: 10.5768/JAO202243.0501005
The pulse width modulation (PWM) drive plays a pivotal part in the servo driving system. Therefore, the filters become more important in differential mode and common mode for pulse width signal ahead of direct current motors. The filter circuit was built with the WSA38M power amplifier module in a photoelectric inertial stabilized turret. The PWM drive switch frequency was analyzed, which caused motor heating and electromagnetic coupling interference. The electric parameter of LC filter was calculated and the optimization simulation was carried out. The results of test and electromagnetic compatibility experiments show that the optimized electrical performance is excellent, especially the 22 kHz~53 kHz frequency band has less interference to the system, which is easy to meet the overall index requirements, and provides a reliable basis for the control system design.
Design of linear CCD acquisition system based on high-resolution spectrometer
KANG Zhen, LIU Jianping, SUN Shuai, PU Peipei, NIU Jing, MA Shibang
2022, 43(5): 864-869. doi: 10.5768/JAO202243.0501006
To meet the technical requirements of high sensitivity, high resolution and low noise of high-resolution spectrometer, the back-illuminated CCD driving circuit and main control circuit for low-level-light imaging system were designed. The MAX X series FPGA of Altera was adopted by linear CCD acquisition system as the core control device to provide multiple driving signals for the linear CCD. The output analog signal of linear CCD was transformed into digital signal after signal preprocessing and AD sampling, and then sent to the spectrometer through USB interface module. By installing the linear CCD acquisition system into the high-resolution spectrometer to test the characteristic peaks of the mercury lamp spectrum, the spectral resolution can reach 0.062 nm, which meets the detection requirements of high-resolution spectrometer.
Design and application of photoelectric auxiliary decision system for FPSO crude oil offloading
ZHU Jinquan, YANG Xueli, SUN Kecheng, LIU Donghui, NIU Zhigang
2022, 43(5): 870-878. doi: 10.5768/JAO202243.0501007
In view of the problem of wind-wave-current mutation of floating production storage and offloading (FPSO) during the offloading production that was easy to cause large angle deviation between FPSO and shuttle tanker, and other problems such as mooring hawser damage or collision accident, a system for real-time monitoring the wind-wave-current, mooring hawser tension and relative position between FPSO and shuttle tanker during the offloading production of FPSO was developed. Based on the monitoring data of optical detection equipment, integrating the existing wind-wave-current data and mooring hawser tension on FPSO, the numerical simulation method was used to establish the mathematical model of prediction of the relative included angle between FPSO and shuttle tanker, so that the functions of real-time monitoring, prediction and early warning of the system were realized. The field test results show that the monitoring data delay of the system is ≤0.5 s, the distance measurement error is ≤0.4 m, the included angle measurement error is ≤0.2°, and the prediction accuracy of included angle within 120 s is ≥80%, which meets the engineering application requirements and provides a technical reference for realizing the intellectualization of the FPSO tandem offloading.
Indoor lighting energy-saving control method based on genetic simulated annealing algorithm
GUO Jing, ZHANG Yujie
2022, 43(5): 879-885. doi: 10.5768/JAO202243.0502001
The current energy-saving lighting control algorithm still falls into the problem of local optimum. In order to seek for the global optimal solution and improve the energy-saving effect of indoor lighting, a genetic simulated annealing algorithm was designed to optimize the control parameters of lighting system. The local search ability of the algorithm was enhanced by simulated annealing treatment of excellent individuals after genetic manipulation. According to the number of iterations and the fitness of the population, the genetic probability was adaptively adjusted so that the algorithm could enrich the population diversity in the early stage and avoid the prematurity of the algorithm. An illumination model based on artificial neural network was proposed to calculate the indoor illumination distribution and evaluate the illumination comfort, which provided a basis for constructing the fitness function of optimization algorithm. Through simulation experiments, the genetic simulated annealing algorithm was applied in the introduced lighting scenes, and compared with the traditional particle swarm algorithm and genetic algorithm, the lighting energy-saving performance was 5.30% and 13.61% higher respectively.
Area mapping for water and forest based on satellite hyper-spectral remote sensing
TANG Wenrui, MA Lin, ZHU Siqi, LIN Sifan, JIA Longze
2022, 43(5): 886-892. doi: 10.5768/JAO202243.0502002
The emergence and development of hyper-spectral satellites provide a new technical means for remote sensing and mapping. Compared with the traditional satellite images, the hyper-spectral satellite images contain the richer spectral information, which can carry out more accurate identification, classification, positioning and mapping of target objects. Taking the hyper-spectral satellite images provided by the Zhuhai No. 1 hyper-spectral satellite (OHS-C) as the sample, the accurate identification, enhanced marking and area measurement of forest and water were realized by combing ground clutter reflection spectrum with adaptive algorithm. The ratio method was used to process the spectrum, and the influence of atmospheric conditions and time as well as season on the spectrum can be removed without the complex calibration. The experimental results show that the specificity and sensitivity of identification of forest and water is higher than 97%, respectively. Based on the proposed identification model, the calculated total area of the official waters of Xili Reservoir is about 4.6 km2, and the error with the official data is only about 0.144 6 km2. The green area of Qi'ao Island is calculated to be 22.171 3 km2, and the total area of the island is 23.8 km2. According to the calculation of 90% of the green area, the error is less than 0.751 3 km2, and the error mainly comes from the insufficient spatial resolution of commercial satellites.
Hyperspectral target tracking based on attention mechanism and additive angular margin loss
SHI Zonghan, ZHAO Haitao
2022, 43(5): 893-903. doi: 10.5768/JAO202243.0502003
With the development of computer technology, the target tracking methods based on deep learning have become an important research direction in the field of computer vision. However, the target tracking methods still face great challenges in complex environment such as background interference and color proximity. Compared with the traditional color images, the hyperspectral images contain rich radiation, spatial and spectral information, which can effectively improve the accuracy of target tracking. A method was proposed in combination with attention mechanism and additive angular margin loss (AAML) to perform target tracking for hyperspectral images. The features of different combinations of bands were extracted by fused multi-domain neural networks, and then the fused attention mechanism model was designed to make the similar features from different combinations of bands integrated and strengthened. Therefore, when the target background color was similar, the network would pay more attention to the target object, which made the tracking results more accurate. On this basis, in order to make the distinction between target and background more discriminative, the AAML was adopted as loss fuction to effectively reduce the intra-class distance of similar samples, increase the inter-class distance between centers of positive and negative samples, and improve the network accuracy and stability during the training process. The experimental results show that the accuracy and success rate of the two tracking accuracy evaluation indexes can be improved by 1.3% and 0.3% respectively, which has more advantages than other methods.
Thread image evaluation method based on machine vision
WANG Jie, CHEN Manlong, LI Kui, YANG Fan, YAN Lizhi
2022, 43(5): 904-912. doi: 10.5768/JAO202243.0502004
In order to improve the measurement accuracy of machine vision thread, an evaluation method based on thread image quality was established. Through the analysis of the line gray-level distribution of the thread gray images and the optical imaging characteristics of the thread, the mechanism of the thread image edge distortion caused by the helix angle was revealed. Based on the analysis of the performance of various thread image evaluation methods, the evaluation algorithm L-yakuo based on the thread edge was adopted to calculate the evaluation value of multiple thread images with different object distances. Finally, the experimental comparison and analysis of the M14×2, M20×2.5 thread angle obtained by machine vision and the thread angle obtained by contact measuring instrument were carried out. The experimental results show that after the clearest tooth profile image is obtained by the L-yakuo algorithm, the machine vision thread angle is calculated, and the accuracy of the thread angle of M14×2 and M20×2.5 is improved \begin{document}$ 9'33'' $\end{document} on average. With the help of L-yakuo algorithm, it can sensitively reflect the definition of thread profile, which basically meets the evaluation requirements of thread image definition. The changes of the evaluation value are basically the same as the changes of the relative error of the thread angle, and the evaluation value has the characteristics of high accuracy and easy to calculate.
Super-resolution reconstruction of fiber optic coil image based on lightweight network
ZHANG Qianchuang, GUO Chenxia, YANG Ruifeng, CHEN Xiaole
2022, 43(5): 913-920. doi: 10.5768/JAO202243.0502005
In order to improve the winding image resolution of the optical fiber coils and reduce the memory and computational overhead caused by the deep learning model, a dual-branch network that can simultaneously extract the gradient information and image information was proposed. The image features in the network path were extracted by using the advantages of speediness and light weight of lightweight residual blocks, and the multi-stage residual feature transfer mechanism was also introduced. Under the combined action of gradient information and feature transfer, the network could retain the rich geometric structure information, which made the edge details of the reconstructed image clearer. The experimental results show that, the proposed model achieves superior performance with fewer parameters and a running time of 0.018 s. Under the double, triple and quadruple scale factors, the peak signal-to-noise ratio is 44.08 dB, 41.35 dB and 38.97 dB, respectively and the structural similarity index is 0.985 8, 0.979 3 and 0.976 9, respectively, which are both superior to other existing methods and provide a strong guarantee for subsequent quality detection of optical fiber coils.
Incremental structure from motion algorithm based on weighted scene graph
JIANG Tao, MA Yong, HUANG Jun, WANG Hesong, FAN Fan
2022, 43(5): 921-928, 1014. doi: 10.5768/JAO202243.0502006
The structure from motion (SfM) is a reconstruction algorithm that recovers the pose of cameras and three-dimensional structure of the target by calculating the image matching relationship. An incremental SfM algorithm based on weighted scene graph was proposed. Firstly, a weighted scene graph was established, which quantified the matching relationship between image pairs. Secondly, an optimal initial seed pair of degree perception was searched based on the edge weights of the weighted scene graph. Finally, the next optimal image candidate set was constructed according to the connectivity of the reconstructed vertices, and an evaluation algorithm based on the vertex degree and feature point distribution was designed to search for the next optimal image in the candidate set. The experimental results on multiple public datasets show that the proposed algorithm outperforms existing advanced structure from motion algorithms in terms of reconstruction quality, camera calibration rate and point cloud generation quantity. Compared with the benchmark comparison algorithms, the average reconstruction time on different datasets is reduced by at least 19%, and the point cloud generation rate is increased by at least 21%.
Spray angle measurement method based on grayscale image differential gradient
WEI Yongjie, LI Mingkai, WANG Haoran, ZHANG Shuri
2022, 43(5): 929-934. doi: 10.5768/JAO202243.0503001
The spray boundary and spray angle work as important characteristic parameters of spray field, which are mainly measured by image method. In image processing, the grayscale images are generally converted into binary images firstly. Then, the binary images are processed and calculated. Due to the multiphase flow characteristics of spray field, there is no judgement basis whether the obtained binary threshold and the image are consistent with the actual spray field. In order to digitally judge the spray field boundary, it was proposed to process directly according to the grayscale image of the spray. The mask templates were obtained and applied to the grayscale image, and then the gradient value of the grayscale image were calculated and compared by image morphology and iterative method. The spray field boundary and the spray angle were calculated by obtaining the grayscale image when the gradient value was maximum. Experimental results show that the proposed method provides a numerical judgement basis to judge and extract the spray field boundary through the gradient maximum value. Thus, the spray field boundary extraction and the spray angle fitting measurement are realized automatically by the program.
Calibration and stability control for photoelastic modulator using feedback optical path
LI Kewu, WANG Shuang
2022, 43(5): 935-942. doi: 10.5768/JAO202243.0503002
In order to achieve the accurate calibration and long-time stable operation for photoelastic modulator (PEM), a calibration and control scheme of phase retardation amplitude which using feedback optical path was established, and the spatial distribution of phase retardation amplitude on the PEM optical aperture was theoretically calculated and simulated. An integrated calibration feedback optical path was designed deviating from the center of PEM. Combined with the phase retardation amplitude calibration method using the ratio of harmonic terms, the digital phase lock technology was used to simultaneously extract the harmonic terms of the modulated light intensity signals from the feedback optical path, and then the phase retardation amplitude of PEM was solved. According to the proposed scheme, the PEM physical object was processed, and the calibration experiment and stability control experiment were both carried out. The experimental results show that, the relative deviation between the calibration value and measured value of phase retardation amplitude of PEM center does not exceed 0.22%. With the use of feedback optical path to control the PEM about 100 minutes, the standard deviation of PEM phase retardation amplitude is 0.001 8 rad and the maximum deviation is lower than 0.42%, which realizes the accurate and real-time calibration of PEM phase retardation amplitude and the long-time stable control of PEM is also verified.
Effect of phase object position on results of Moire deflectometry
CHEN Yayi, CHEN Yunyun, ZHANG Jingyun, YANG Cuihong
2022, 43(5): 943-949. doi: 10.5768/JAO202243.0503003
The Moire deflectometry has been widely used in the structural display and key parameter measurement of various flow fields, and there have been different researches for the placement of phase objects in the optical path. The theoretical and experimental studies were carried out on this issue. Theoretical analysis showed that when the measured object was placed in front of two gratings, the offset and phase mainly depended on the distance between two gratings, while the deflection angle was determined by the ratio of phase disturbance and the distance of the two gratings. However, when the measured object was placed between two gratings, the offset and phase mainly depended on the distance from the measured object to the next grating, and the deflection angle was determined by the ratio of phase disturbance and the distance from the measured object to the next grating. In order to verify the correctness and rationality of the theoretical results, a candle flame was taken as an example for experiments. Furthermore, the comparison shows that in two cases, the position of the measured object will not affect the final phase and deflection angle reconstructed in the experiment, as long as the distances mentioned above are suitably chosen. The relevant research results can provide a certain reference for the better use of Moire deflectometry in the detection of various flow fields.
Optimal compensation methods of wedge angle of reference mirror in equal optical path interferometers
ZHU Huaikang, ZHANG Qiyuan, HAN Sen
2022, 43(5): 950-958. doi: 10.5768/JAO202243.0503004
When measuring multi-surface parallel samples, the multi-surface interference can affect the measurement results. To improve the multi-surface interference problem, an equal optical path interferometer was introduced and the optimal method to compensate for the wedge angle of reference mirror was studied. In an equal optical path interferometer, due to the existence of wedge angle and inclination angle of the reference mirror and beam splitter mirror, the retrace errors would occur in the measurement results. The different compensations were applied depending on the different cases of reference mirror wedge angle. The placement and compensation amount of the various compensations were theoretically analyzed and determined, and the effect of the size of inclination angle and wedge angle on the height of the beam to be blocked and the image square NA was studied. The interferometer simulations were then carried out using Zemax with different compensation methods, and the magnitude of the retrace error was analyzed according to the PV values of the interferograms obtained from the simulations. The analysis shows that the optimal compensation method is chosen, with a wedge angle of reference mirror of 1′ and the retrace error is better than 0.003 wavelengths.
Error analysis on dihedral angle of corner-cube reflectors in Fourier transform spectrometer
HU Jingsen, HUANG Min, GAO Han
2022, 43(5): 959-966. doi: 10.5768/JAO202243.0503005
Fourier transform spectrometer is an important spectral analysis instrument. To research the influence of the dihedral angle error of corner-cube reflectors on interference quality of oscillating Fourier transform spectrometer, the theoretical analysis and computer simulation were carried out. According to the oscillating Fourier transform spectrometer model, the mathematical expressions of the interference intensity and modulation depth with dihedral angle error were deduced. The tolerance of dihedral angle was determined by the modulation depth criterion. The optical design software Zemax was used to establish the model for simulation and verify the results of theoretical derivation. According to the modulation depth criterion, the tolerance of dihedral angle obtained by the theoretical model is 2.52″, and that obtained by the Zemax simulation is 2.38 ″. The error is 0.14 ″, which is acceptable. The analysis results show that the established theoretical model is reasonable, which has certain reference value for the design and installation of oscillating Fourier transform spectrometers.
Light source calibration for divided focal plane polarization imaging system
ZHAO Yonggang, SUN Chunsheng
2022, 43(5): 967-972. doi: 10.5768/JAO202243.0503006
Polarization imaging technology under water is a hot spot in the research of underwater imaging. Due to the great attenuation of natural light in water, the underwater imaging system mostly adopts active illumination method. In order to solve the problem that the polarization information of acquired images was biased due to the mismatch of polarization direction between polarization illumination source and polarization detection element in divided focal plane polarization imaging system, which affected the quality enhancement of target images, a light source calibration method for divided focal plane polarization imaging system was proposed. First, the calibration principle of polarized light source was described, then the implementation steps of polarized light source calibration were given. Finally, the underwater target images before and after calibration were enhanced and the image quality was evaluated by using polarized dehazing algorithm and image quality evaluation method. The evaluation results show that the quality of the calibrated image restoration is better than that of the uncalibrated image restoration, and the average gradient can be improved by 2.48 times at most. The proposed calibration method is simple, effective and practical, which is suitable for the calibration of polarized light source in divided focal plane polarization imaging system.
Application of PWM dimming based on Grassmann optical model
LI Zongqian, SHI Yan, LIAO Yinghua, LUO Yi
2022, 43(5): 973-979. doi: 10.5768/JAO202243.0505001
For the difficulty to accurately regulate the color and luminous flux of light-emitting diode (LED) light source, and the regulation operation needs to be carried out in computers and other equipment in the production and application, a mathematical model representing the relationship between pulse width modulation (PWM) and LED illumination based on the Grassmann color law and the characteristics of PWM in regulating LEDs was proposed. The RGB LED dimming and color matching system was designed with STM32 microcontroller as the core. The monochrome, double-color, and trichrome mixed illumination experiments were performed on the system. The comparison between the measured value of the digital illuminometer and the theoretical value of the illumination mathematical model proves that the illumination error of the system in the range of 0~370 lx is less than or equal to 4%, and a total of 16 777 216 kinds of light colors can be synthesized. The control of the color and luminous flux of the light source can be accomplished directly on the system without connecting to other equipment, which can reduce the operation process and meet the color and illuminance requirements for industrial visual detection, crop fill lighting and cultural tourism.
Ultra-thin silver transparent conductive film based on aluminum infiltration layer
LI Dong, PAN Yongqiang, LIU Huan, ZHENG Zhiqi, ZHOU Zelin
2022, 43(5): 980-985. doi: 10.5768/JAO202243.0505002
The ultra-thin silver film is a potential material used for transparent conductive electrodes because of its high flexibility and excellent photoelectric properties. The ultra-thin silver transparent conductive films were prepared by resistance thermal evaporation technology using aluminum as infiltration layer. The threshold thickness of the silver film was reduced by introducing an aluminum infiltration layer, so that the silver film could be continuous on the K9 glass substrate at the lowest possible thickness. The resistance of silver film squares on aluminum infiltration layers with different thicknesses was tested, and verified by scanning electron microscope (SEM) images that the 1 nm aluminum infiltration layer had better infiltration effect on silver film. Then, the silver films with different thicknesses were prepared on 1 nm aluminum infiltration layer by the same process. The transmittance and square resistance test results show that the square resistance of 10 nm silver film prepared on 1 nm aluminum infiltration layer can reach 13 Ω/□, and the transmittance can reach more than 50% in the range of 0.4 μm~2.5 μm.
Optically switchable multifunctional terahertz geometric phase metasurface
FAN Junpeng, WANG Xiaozhao, ZHANG Jianxin, ZHANG Zhen, SUN Cai, HU Qiyong
2022, 43(5): 986-993. doi: 10.5768/JAO202243.0505003
An optically switchable terahertz metasurface was proposed based on the metal-photosensitive silicon combination rings, which could be used to achieve multifunctional wavefront control. The metasurface was composed of double-sided structural layers and an intermediate medium layer, from which the structural layers were metal rings with opposite opening directions, and the opening was filled by photosensitive silicon. At a lower light intensity, the metasurfaces could convert the incident circularly polarized waves into cross-polarized transmitted waves. As the light intensity increasing, the transmitted waves would be completely suppressed. Based on the geometric phase principle, by rotating the metal-photosensitive silicon combination ring, the transmitted cross-polarization wave would carry additional phase factors, and could achieve a complete 2π-range phase coverage. By properly arranging the metasurface unit structure, the wavefront of the transmitted wave could be manipulated arbitrarily. The proposed optically switchable metasurface enabled an efficient anomalous refraction, metalens and orbital angular momentum generator under lower light conditions, while the transmission efficiency was suppressed and the application function could be conditionally selected under higher light conditions, which showed the better flexibility. Therefore, the proposed device has great potential applications in terahertz imaging, communication, radar, and etc.
Real-time positioning technology of train based on optical fiber coherent Rayleigh backscattering
ZHANG Xinwei, LI Jun, ZHANG Dingbo, YAN Ruijin, TIAN Biao, DING Guoshen, YIN Heyi, MA Tian, WANG Weifeng, ZHAI Xiaowei
2022, 43(5): 994-1000. doi: 10.5768/JAO202243.0508001
With the rapid growth of railway mileage in China, the degree of heavy load of railway wagons continues to increase. An interference technology based on Rayleigh backscattering signal in optical fiber was proposed by using existing communication optical cables along railway lines. When the fiber vibrated slightly, the phase and refractive index of the fiber at disturbed position changed, which resulting in the Rayleigh backscattering light. By performing differential calculation on the Rayleigh signal curves before and after the operation, the location of the interference light intensity signal corresponded to the location of the disturbances was obtained. Based on this method, the recognition and positioning of railway vehicles were realized. By collecting and analyzing the time-domain and frequency-domain signal, the signal strength, train length, the number of carriages and other characteristics were extracted, and the model of railway vehicles were accurately recognized. Compared with traditional positioning technologies, this technology could realize long-distance monitoring, and the sensing fiber was buried underground on both sides of the railway, which was conducive to the concealment and protection of optical fiber. Experimental results show that the positioning error of the system is within ±10 m, and the detection of railway speed and position within 25 km can be realized.
Package of hollow micro-bottle resonator and refractive index sensing properties
ZHAO Shuaichang, WANG Zijie, LIU Xiaochen, WANG Kehong, CHEN Yiqi, YANG Yong, ZHANG Qi, ZHANG Xiaobei
2022, 43(5): 1001-1006. doi: 10.5768/JAO202243.0508002
To improve the stability and portability of the sensor, a refractive index sensor based on hollow micro-bottle resonator was proposed to package the system and study its refractive index sensing properties. The optical field distribution of radial echo-wall mode of hollow micro-bottle resonator under different wall thicknesses was simulated and analyzed. The proportion of the optical field inside the micro-bottle increased with the decrease of wall thickness of device, which was beneficial to improve the sensing sensitivity. To reduce the wall thickness, the quartz capillary was etched by hydrofluoric acid, which was used to fabricate the thin-wall hollow micro-bottle resonator by fusion splicer. The coupling system was packaged and fixed on a slide by using UV adhesive, which enhanced the stability and portability of the sensor. Finally, the sensing characteristics of the packaged device under different refractive index matching fluids were studied and the sensing sensitivity was 26.50 nm/RIU. The proposed sensor has the advantages of high stability, high flexibility and low loss, which has great application potential in optofluidic refractive index detection.
Circumferential stress measurement of blood vessels model in vitro based on fiber Bragg grating sensor
ZHANG Yan, ZHANG Fan, ZHAO Guanqi, CHU Daping
2022, 43(5): 1007-1014. doi: 10.5768/JAO202243.0508003
The circumferential stress caused by blood flow in blood vessels is closely related to the structural and functional changes of blood vessels. Measuring the circumferential stress of blood vessel models in vitro is an important issue in biomechanics research. A method for measuring the circumferential stress of blood vessels by using fiber gratings was proposed, and a three-dimensional circular blood vessel model integrating fiber gratings was established by using steel needle mold based on microfluidic technology. The relationship between different flow velocities and stress was studied through simulation. The simulation results show that the stress changes linearly with the flow velocity in the range of 8 mm/s~75 mm/s. The circumferential stress generated by fluid flow was measured by fiber Bragg grating sensor. According to the experiment, the relationship between wavelength change of grating and velocity was obtained. When the flow velocity range varies from 8 mm/s to 75 mm/s, the wavelength change caused by velocity is 0.173 nm. The relationship between stress and wavelength change of grating was obtained by simulation experiment. A microfluidic blood vessel model with fiber Bragg grating sensor was proposed and implemented, which provides a new idea for measuring circumferential stress in vitro when blood flows.
Design of broadband hybrid fiber amplifier based on particle swarm optimization algorithm
GONG Yi, LIU Fang, MENG Fanke
2022, 43(5): 1015-1021. doi: 10.5768/JAO202243.0508004
Based on the theoretical model of Erbium-ytterbium doped fiber amplifier (EYDFA) and the analysis theory of stimulated Raman scattering effect, a hybrid amplifier structure combining EYDFA with second-order multi pump Raman fiber amplifier (RFA) was studied and designed by using the gain spectrum complementary characteristics of EYDFA and RFA. In order to obtain a hybrid amplifier with high gain and low flatness, a particle swarm optimization algorithm was introduced to optimize the pump wavelength and power. The simulation results show that, without the use of gain equalizer, the output power of the designed hybrid fiber amplifier is approximately equal, the average gain is 38.78 dB and the gain flatness is 1.1 dB in the bandwidth range of 90 nm, which provides a reference for the design and optimization of the hybrid amplifier.
ENZ material filled microstructured optical fiber with high birefringence and near-zero flattened dispersion at terahertz frequency
WEI Jiaoxia, WANG Doudou, ZHANG Yue, TIAN Jiangkun, YUE Shuai
2022, 43(5): 1022-1029. doi: 10.5768/JAO202243.0508005
The high birefringent microstructured optical fiber (MOF) with small defective holes in fiber core and elliptical cladding air holes was designed for polarization-maintaining waveguide transmission for terahertz wave. By selectively filling the terahertz epsilon-near-zero (ENZ) materials in cladding air holes, the dual asymmetry of the geometric structure and the material distribution was introduced, and the degeneracy of two polarized fundamental modes was broken to obtain the high birefringence. The variation of transmission properties such as birefringence, loss and dispersion with structural parameters was studied by finite element method (FEM). In the wide-band range from 0.5 THz~2 THz, the high birefringence greater than 0.01 was obtained. The loss of the x-polarized and y-polarized fundamental mode has the minimum value around 0.8 THz, which are 0.903 dB·cm−1 and 0.851 dB·cm−1, respectively. The dispersion characteristics can be effctively adjusted by the defective holes in fiber core, and the y-polarized fundamental mode has the near-zero flattened dispersion characteristics of (0±0.054) ps·THz−1·cm−1 in the range of 1 THz~1.8 THz. The transmission characteristics of the designed fiber are insensitive to the refractive index changes of ENZ material. The research conclusions provide theoretical references for the development of terahertz polarization maintaining fiber.
Laser communication performance of UAV slant based on MIMO
TANG Hanling, LI Yongjun, LI Yi, ZHAO Shanghong
2022, 43(5): 1030-1036. doi: 10.5768/JAO202243.0508006
The downlink single input multiple output (SIMO) and uplink multiple input single output (MISO) technologies of laser communication of unmanned aerial vehicle (UAV) air-ground slant in atmospheric turbulence channel were studied. Based on the atmospheric turbulence model of Gamma-Gamma distribution, the Meijer function was used to derive the bit error rate (BER) closed expression of SIMO technology in downlink under the combined influence of atmospheric turbulence and pointing error. An approximate expression of BER performance of MISO technology in uplink of Gamma-Gamma turbulence model was established based on \begin{document}$ \alpha - \mu $\end{document} distribution. The effects of antenna number, zenith angle and pointing error on the system were studied systematically. The results show that the spatial diversity technology can effectively improve the BER performance of the system. When the beam divergence angle is 500 μrad, and the downlink receiver as well as the uplink transmitter are 3, the performance optimization can be over 10 dB. The zenith angle has a significant influence on the BER performance of air-ground slant laser communication. In order to meet the performance requirement of 10−6 of system BER, the zenith angle should be controlled within a small range of about 30 degrees.