2016 Vol. 37, No. 6

OE System and Engineering
Study on bioagents/bioaerosols remote sensing technology by lidar
Yang Hui, Zhao Xuesong, Sun Yanfei, Wang Tiedong
2016, 37(6): 783-788. doi: 10.5768/JAO201637.0601001
Based on two physical phenomena,laser induced fluorescence (LIF) and depolarization, resulting from elastic scattering on nonspherical particles, a compact lidar system for realtime standoff detection of bioagents/bioaerosol is developed. The system includes three laser sources, two receiving telescopes, depolarization component and spectral signature analyzing spectrograph. For the horizontal polarization measurements, it can be concluded that,1) the depolarization ratios are wavelengthdependent; 2) the discrimination efficiency increases significantly with the number of wavelengths used. And from the depolarization timespace distributions results, it can be revealed that, the aerosol depolarization ratio remains at a low level within the boundary layer, and can be affected by the wind, humidity, temperature and other meteorological factors, the complex zigzag vertical distributions of depolarization ratio is obvious in the tropospheric layer, the depolarization can reach 0.3 at some clouds. Finally, the Mie scattering observation results with the 532 nm and 355 nm wavelengths show that the more complicated layered structure of aerosol timespace distribution can be obtained with the 355 nm wavelength if the output energy of two wavelengths are at the same level.
Light and information
Francis T. S. Yu
2016, 37(6): 789-795. doi: 10.5768/JAO201637.0601002
Light is not just the major source of energy that supports life and it is also a very viable information carrier. In this article, we showed that there is an intimate relationship between information and light as a carrier. We discussed the Uncertainty Principle of Heisenberg as related to information, in which we showed that every bit of information (or quanta of light) is limited by an unit cell of information and it is associated with a cost of entropy. Examples are given within the limit and beyond the Uncertainty Principle. We have shown that time and frequency resolutions cannot be observed simultaneously and yet the imaging can also be obtained within the limit of Certainty!
Analysis on ground scattering signal of Doppler lidar in space
Li Zhigang, Liu Zhishen, Oliver Reithbuch
2016, 37(6): 796-803. doi: 10.5768/JAO201637.0601003
In order to expand the application of ground scattering signal for Doppler lidar in space, the characteristics of ground return in intensity, elevation and velocity are analyzed by using the flight data of several airborne Doppler lidars. The backscattering ratio of ground to the upper atmosphere can be used to reflect equivalently the ground reflectance properties,the comparison of ground elevation derived from lidar signal and digital elevation model shows a good consistency, with a mean deviation below 20 m and a standard deviation below 100 m; the dopper information of ground return can also be used for the plane speed correction, and the results shows a good consistency to the platform data results, with a standard deviation below 1.5m/s for direct detection system and 0.5 m/s for coherent detection system. The feasibility of velocity correction using ground return is verified. Besides these, a new method for the discrimination of cloud and ground return in a way of elevation comparison is proposed and analyzed.
Influence of laser power on stiffness calibration of optical tweezers
Zhang Yuling, Zhou Zhehai, Zhu Lianqing
2016, 37(6): 804-810. doi: 10.5768/JAO201637.0601004
The stiffness of optical trap has become an important parameter to describe the manipulation capacity of optical tweezers to particles, which can be affected by laser power. The equipartition theorem and Boltzmann statistic methods were used to calibrate the stiffness of the built optical tweezers, where an image acquisition method was used to measure the particles displacement, and the calibrated results based on these two methods were compared, which showed good agreement. Furthermore, the influences of sample cells laser power on the stiffness were studied. In order to increase the accuracy of stiffness, the amplification factor of light path and temperature should be considered. Seen from the results, the two calibration methods have similar results; the optical trap stiffness increases linearly with the laser power on the sample cell for lower power 1 mW~20 mW, but shows a tendency toward stabilization for higher power 25 mW~60 mW. Whats more, the calibrations accuracy of light path amplification brings a great impact, a 10% relative variation leads to a 23% offset of stiffness, and the temperature has a little influence, a variation of 0.1 ℃ results in 0.034% variation.
Optical design of panoramic annular imaging Fourier transform spectrometer
Chen Youhua, Lyu Ze, Li Kewu, Wang Zhibin
2016, 37(6): 811-817. doi: 10.5768/JAO201637.0601005
A novel imaging Fourier transform spectrometer structure was proposed, which included two confocal hyperboloid mirrors as the collector and a Schwarzchild objective for collimating, combined with the photoelastic modulator based interferometer, imaging lens and HgCdTe focal plane array, then the infrared panoramic annular spectral imaging was achieved. In this paper, the working principle and imaging features of panoramic annular imaging Fourier transform spectrometer were introduced, the design of two confocal hyperboloid mirrors based annular collector and Schwarzchild objective based collimator were discussed in detail, then the design model and optimization scheme were presented. Finally, the ray tracing and optimizing were done by Zemax. Results show that, the working band of designed imaging Fourier transform spectrometer is 8 m~12 m, the effective focal length is -0.67 mm, the lateral field of view is 40~80and the F number is 0.9, the rootmeansquare (RMS) spot radius is 20.116 m less than a pixel, all field modulation transfer function (MTF) at 16 lp/mm are higher than 0.5 with good consistency, the optical path difference(OPD) is within 0.4 scope, the imaging quality of the system is fine.
Weak light uniform light system for LLL ICCD parameter calibrating device
Wang Shengyun, Shi Jifang, Li Hongguang, Zhang Boni, Xie Qi, Sun Yunan
2016, 37(6): 818-822. doi: 10.5768/JAO201637.0601006
In lowlightlevel(LLL) imageintensified charge coulped device (ICCD) parameters measurement, in order to obtain the testing parameters such as the resolution, the signaltonoise ratio, the minimum intensity of illumination and the image plane uniformity, the integral ball weak diffuse light system with wide dynamic range is required. Through analyzing the structure and limitation of the traditional light source, and according to the different requirements for the light intensity of illumination in LLL ICCD synthetic parameter tests, a wide dynamic range diffuse light system was designed. The light source system utilized the doubleintegral ball mode, and through using the wedge gradient variable aperture diaphragm and implementation, the continuous changing of illumination under the constant color temperature was realized, and the uniform diffuse light source with different intensities of illumination ranges was formated. Furthermore,the weak light illumination output range and uniformity of LLL ICCD parameter calibrating device were measured. Results show that the emergent light illumination range of the light source is 10-7lx~103 lx,the emergent light uniformity is 98%, the light source is suitable for measuring the LLL ICCD performance parameters.
Optical axis parallelism calibration system of large scale multispectral multioptical axis
Yan Zongqun, Yang Jianchang, Xie Zhihong, Yu Hao, Shi Yunsheng
2016, 37(6): 823-838. doi: 10.5768/JAO201637.0601007
In order to calibrate the optical axis parallelism of multispectral photovoltaic equipment indoor without dismantling the integrated equipment or vehicle, we designed a optical axis calibration system. The system provided a plurality of spectral bands infinity object by a multispectral collimator, realized the large span translation of collimator indoor through a twodimensional mobile platform, restored and ensured the optical axis parallelism of the collimator before and after translation using the tilt sensor, the doublelinear array charge coulped device (CCD) measurement system and the posture adjustment mechanism. The optical axis parallelism of optoelectronic equipments indoor, at different positions on vehicle with different optical axis distances and spectral bands, was calibrated by onetime. Moreover,we analyzed the design and error of the all subsystems. The results show that the system total error of the optical axis parallelism before and after translation is less than 0.142 mrad, this system can both improve the calibration accuracy and reduce the workload of the optical axes calibration. The errors of tilt sensor and position adjustment mechanism have the greatest contributions to the total system error, the system would have a higher system accuracy by selecting subsystems with higher accuracy, and could meet the requirement of more precision optical axes calibration.
Study on making color hologram of large object
Gan Liangqin, Yang Shanggong, Xu Daisheng, Xu Yingchao, Du Xuri
2016, 37(6): 829-832. doi: 10.5768/JAO201637.0601008
Based on analyzing the relationship among the hologram spatial frequency, the object size and the hologram record distance in making the color hologram by twostep method,a method for making color hologram of large objects was proposed. Firstly, the tricolor hologram H1rgb was recorded in visual plane after intercalating right parameters, so as to make sure the full information were recorded in the least area and when H1rgb placed in the same plane, their reappeared images could overlap. Then, the overlapped images were recorded to acquire the color hologram after the information of objects were enlarged by the conjugate light. This method can enlarge the field of view(FOV) and sit for making hologram of large objects. It is verified by experiment that the FOV can be widen by 6 times.
Design of large area MCP electron rinse and test system
Song Chengxin, Qiu Yafeng, Qian Yunsheng, Tang Liming
2016, 37(6): 833-838. doi: 10.5768/JAO201637.0601009
Electron rinse process is an effective way to improve the performance of microchannel plate (MCP).In view of the domestic electron rinse and test system only applied to the MCP with diameter of 30 mm and above at presents, an electron rinse and test system with 4 stations for largearea MCP (500 mm100 mm) was designed.In this system, the electron rinsing of MCP could be conducted on each station at the same time,and the parameters could be tested at one of the stations in the process of the electron rinsing at different stages.4 stations in the vacuum system could be converted to each other quickly.By emitting a uniform ultraviolet light on the gold cathode, the uniform electrons were generated, then an adjustable uniform electron beam could be obtained after uniform electrons being increased by standard MCP(105 mm).Through vacuum, leakage detection and baking processes by several times,the time reaching the vacuum degree of 510-4 Pa was obtaind within 45 min, and the limit vacuum degree was better 510-4 Pa, which could meet the index requirement of rinsing and testing.For measuring the effect on the vacuum pumping difficulty of the vacuum system brought by the load, the factor K was defined in the experiment progress.Calculations show that the value of K was in the range of 0.35~1.57, and the positive proportion of factor K and pumping difficulty of the system was revealed.
Tanker pose prediction based on modified unscented Kalman filter
Fu Yi, Kong Xingwei, Dong Xinmin, Zhi Jianhui, Gao Yu
2016, 37(6): 860-865. doi: 10.5768/JAO201637.0602004
Aiming at the low accuracy problem of the tanker pose tracking in the autonomous aerial refueling, a modified unscented Kalman filter(UKF) algorithm was put forward. The mathematical model of vision navigation was established. The Harris method was applied for corner detection, and then the random sample consensus( RANSAC) was used to match the detected corner. The historical forecast data was introduced into the current prediction so that the UKF prediction results could be modified with respect to the observation results from the corner match. As a result, the goal of high accuracy prediction was achieved. Compared with the standard UKF, the experimental results show that the prediction error of the proposed method is smaller than 5.8% which is feasible and effective in aerial refueling. The algorithm can eliminate the prediction error caused by the strong inference so as to effectively suppress the strong interference.
OE Information Acquisition and Processing
Accurate direction detection method of differentscale motion blurred images
Hong Yang, Sun Xiuxia, Liu Shuguang, Lyu Maolong, Hu Jinglin
2016, 37(6): 839-846. doi: 10.5768/JAO201637.0602001
In order to remove the highdynamic infection on image collection, a method based on the characteristic of Fourier spectrum was proposed to solve differentscale motions direction detection. This proposed method used the curvature radio to distinguish the difference between the smallscale or largescale motion. After that, the blurred direction with cepstrum domain or twice Fourier transform can be estimated by differentscale motion. Considering the ratio of the image and cross bright line, a method based on midvalue as a threshold to optimize the image was proposed to acquire the direction of the blurred motion. Experimental results show that proposed method can distinguish the differentscale motion effectively and can improve the precision of motion direction or scale estimation. The robustness of estimation algorithm is improved in comparison with other algorithms, the relative error rate is less than 0.02.
Tunable Airy beam and its propagation properties
Liu Huilong, Xia Jing, Chen Dong, Lyu Yanfei
2016, 37(6): 847-853. doi: 10.5768/JAO201637.0602002
Having dealt with the diffraction effects of a propagating laser, the Airy beam is a new kind of beam with nondiffraction. In our paper, based on the Airytransformation technique, we introduced a novel Airy beam with the tunable tail, which could be generated from the elliptical flattopped Gaussian beam. Through calculation, the Airy beam with the single tail was obtained by adjusting the ration of the beam width of elliptical flattopped Gaussian beam.And the tail length of Airy beam was controlled by the order N of incident beam.Research results show that the acceleration direction of Airy beam is 45 along x axis with p=1, being 31 with p=1/2, and being x positive direction with p=1/3. It can be seen that the acceleration direction of Airy beam could be adjusted by changing the values of p.
Research of background suppression method based on spatialtemporal bilateral filter
Wang Tao, Chen Fansheng, Su Xiaofeng
2016, 37(6): 854-859. doi: 10.5768/JAO201637.0602003
The strong edge in an infrared image is an important factor restricting the infrared dim target detection probability and also an important source of target false alarm. By taking advantages of bilateral filters characteristics of the Euclidean distance of neighbor pixel and the similarity of pixel gray value, as well as the slowchanging interframe background, we defined the spatialtemporal bilateral filter and verified the inhibitory effect of this algorithm in the good complex backgrond. Results show that it can retain the target energy substantial and improve the local signaltoclutter ratio(SCR), the signaltonoise ratio gain(GSNR) is greater than 3.6 and the target energy suppress factor is less than 0.2.
Feature points extraction and matching technology of binocular vision measurement system
Zhang Yihao, Sun Dongmei, Shen Yucheng, Wang Zhenyao
2016, 37(6): 866-871. doi: 10.5768/JAO201637.0602005
A light pen based binocular stereo vision measurement system for largescale workpiece was developed,in which feature points extraction and matching technology were studied deeply. The sub pixel edge of ellipse spot was achieved accurately by the algorithm based on Canny operator and Zernike moments. Based on the ellipse spot edge points, the curve fitting method based on the least square was used to realize the center extraction of the ellipse spot. Aiming at the matching problem of feature points,the matching method based on position constraint was proposed.Experiment results demonstrate that the proposed method can extract the sub pixel edge of the ellipse spot, accurately calculate the center coordinate of the ellipse spot, and the matching rate is greater than 95%.
Optical Metrology and Measurement
Effect of substrate temperature on structure and properties of HfO2 thin films prepared by magnetron sputtering
Xi Yingxue, Liu Zheng, Wang Zhao, Liu Weiguo, Xu Junqi
2016, 37(6): 872-879. doi: 10.5768/JAO201637.0603001
HfO2 thin films were deposited on single crystalline silicon substrate by using magnetron sputtering in totally reactive oxygen plasma. Effect of substrate temperatures on the structure and properties of HfO2 films were investigated. Phase structure, component and surface topography were characterized by using the Xray diffraction analysis (XRD), Xray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. The mechanical properties of the films were measured by using the nanoindentation. It is indicated that the (111)oriented HfO2 films could be obtained and the structure of the asdeposited films was not changed as the increase of the substrate temperature. The stoichiometric ratio, surface topography and nanomechanical properties of the asdeposited films were dependent on the substrate temperature. The stoichiometric ratio would be deteriorated with the substrate temperature increasing, which was attributed to the diffusion of silicon. The best substrate temperature was found to be 200 ℃. The atom ratio of O/Hf for the asdeposited films could arrive to be 1.99. In addition, the lowest value of rootmeansquare(RMS) roughness and the maximum value of hardness and elastic modulus were obtained.
Study on measuring human luminance and color contrast sensitivity visual characteristics and their models
Yao Juncai
2016, 37(6): 880-886. doi: 10.5768/JAO201637.0603002
In order to explore the contrast sensitivity characteristics of human visual system (HVS), using the liquidcrystal display to display the target grating with 11 kinds of spatial frequencies and 3 average brightnesses for 10 cd/m2, 60 cd/m2 and 90 cd/m2, the experiments was designed to measure the data of the luminance and color contrast sensitivity of HVS of 120 youths. After the data was analyzed and fitted by the least square method, a mathematics model mixed with polynomial and exponential was proposed to describe the contrast sensitivity characteristics of HVS. And the model was compared with the typical models at home and abroad. The results show that the human visual contrast sensitivity increases firstly and then decreases with the increase of the spatial frequency, and when the f is 3 cpd~4 cpd, HVS is the most sensitive, which is consistent with the typical visual models. These show the proposed measurement method is effective and feasible, the proposed visual model is scientific. Furthermore, the operation of this measurement method is easy, the calculation complexity of visual model is relatively smaller. They are superior to the typical measurement method and visual models in practical application, which can offer some reference value.
Simulation analysis of influence of SiO2 on thermal stress distribution of multilayer GaN epitaxial wafer
Chen Jing, Cheng Hongchang, Wu Lingling, Feng Liu, Miao Zhuang
2016, 37(6): 887-894. doi: 10.5768/JAO201637.0603003
In order to research the influence of SiO2 on thermal stress of multilayer GaN epitaxial wafer, the surface stresses in sapphire/AlN/GaN and sapphire/SiO2/AlN/GaN epilayers with a diameter of 40 mm were respectively calculated and simulated by the finite element modeling method. The epilayer stress distribution in the radial and axial directions of two epilayers were analyzed with the same other structure parameters, and the thermal stress influence factor was analyzed. The results indicate that the epitaxial wafer thermal stress was uniformly distributed in the radial direction and there were mutations on the substrate and epitaxial layer in the axial direction at 1 200 ℃. Finally the influence of the growth temperature,the GaN and AlN transition layers thickness and the sapphire substrate thickness on surface thermal stress was analyzed.
Absolute measurement method of transmission wavefront distortion of spherical lens
Ma Hua, Yuan Quan, Zhang Lin, Yang Yi, Ren Huan
2016, 37(6): 895-900. doi: 10.5768/JAO201637.0603004
The transmission wavefront distortion of spherical lens is an important factor influcing the light beam quality for high power laser drivers.The precision of spherical lens wavefront measured by Fizeau interferometer is limited by the precision of standard spherical lens and the rear flat. However, the existing absolute testing method applies to reflecting element only. To remove the error of standard spherical lens and the rear flat and improve the test precision of spherical lens transmission wavefront, an absolute method,three positionshifting method, was proposed. The principle of this method was introduced in detail, the simulation and the verified experiment were performed. The simulation results show that the simulation error is 10 nm~13 nm,meeting the theorotical requirement of highprecision measurement; Experiment results show that in spherical lens wavefront measurement, three positionshifting method can effectively reduce the influence of standard spherical lens and rear flat on the measurement results. This method has a good guidance for processing and alignment of spherical lens.
Subsurface defects recognition using thermography based on second order differential peak method of logarithmic coordinates
Xing Xiaojun, Zuo Xianzhang, Shen Si
2016, 37(6): 901-906. doi: 10.5768/JAO201637.0603005
It is difficult to detect subsurface defects on the specimen using thermography. For this problem, different cracks on ferromagnetic 45# steel and nonferromagnetic material aluminum were studied. Cooling curve of different defects on both 45# steel and aluminum were extracted and normalized and then turned into the logarithmic temperaturelogarithmic time curves to obtain a second order differential curve by fitting, furthermore, the minimum peak time of the second order differential was used as the feature quantity to quantified the defect depth. Results show that, as for 45# steel,when the ratio of width to depth is equal to or larger than 2, the relationship between the time corresponding to the minimum peak of second order differential and the square of depth is linear,its possible to measure the depth of the crack. As for aluminum, the time is independent of the depth, and the depth cannot be measured. Finally, the simulation results were verified by experiment.
Optical Element and Fabrication
Design of universal shortfocus projection lens
Liu Xiaochan, Chen chen, Li Weishan, Liu Hongjun, Zhangyu
2016, 37(6): 907-912. doi: 10.5768/JAO201637.0605001
To design a universal shortfocus projection lens for different sizes of projectors, the characteristic optical parameters of which were integrated, and the different sizes of the prism inside the optical engines of different types of projectors were put into the multiconfiguration of the system as one part of the lens. The image height, resolution and back operating distance were set reasonably according to different parameters of the chips. Finally, a lens whose throwratio was 0.8:1 ~0.95:1 for every suited projector based on 1 digital micromirror device (DMD) or 3liquid crystal display (LCD) technology was designed, in which the chip was from 0.63 inch to 0.8 inch. The illumination and distortion problems difficult handled in shortfocus projection system were analyzed, and an effective solution was provided. Furthermore, the tolerance analysis was conducted.
Design of large angle directtype LED backlight lens
Kang Lianjie, Ju Rongbing, Han Ming, Liu Yan
2016, 37(6): 913-918. doi: 10.5768/JAO201637.0605002
Costcutting schemes have been proposed more and more in liquid crystal display (LCD) display field. Aiming at the backlight system of LCDTV, a large angle backlight lens design was proposed. Using a specific doublefree surface design, the first hole is set to be elliptic structural surface, which could classify the emergence luminous flux from light source as equal angle. Based on the corresponding relationship between the ideal illumination distribution of receiving screen surface and the exiting luminous flux of every angle of the first hole, the freeform curve of light emitting surface was calculated. Then by means of microstructure processing at the bottom and according to the requests of mould and molding product,the appearance structure was completed, and finally the scheme meeting the design index was achieved,which could effectively solve the macular problem caused by increased angle and satisfy the evenness requirement for target receiving surface. For a 32 inch LCDTV backlight module, 12 LED lamp beads with the max forward current of 350 mA were utilized, in the system with the module height of 30 mm, the designed backlight lens module could match the demands of brightness and uniformity.
Improved Roman encoding based on DMD
Fu Weiping, Li Jing
2016, 37(6): 919-923. doi: 10.5768/JAO201637.0605003
Holographic lithography can be realized by loading computergenerated hologram(CGH) on digital micromirror device ( DMD) to form the digital mask. Roman encoding is a commonly used method to generate CGH, which uses the height and position of transparent rectangular hole to encode the amplitude and phase of sample unit of hologram respectively. Usually, as reconstructing the binary hologram,the multiple micromirrors of DMD are combined to represent a single rectangular hole, and the utilization and resolution of its pixels can reduce. To solve the problem, an improved Roman encoding is introduced, which can make full use of the binary pulse width modulation of DMD and use the grayscale value to encode the amplitude of the sample unit, convert the transmittance of hologram from binary to grayscale and reduce the number of micro mirrors occupied by a single sample unit effectively. MATLAB is used to build the simulation model to reconstruct and analyze the CGHs produced by improved Roman encoding and Burch encoding. The results indicate that the diffraction efficiency of the improved Roman encoding is 3 times as much as that of the Burch encoding. The reconstruction experiment based on DMD is conducted, which demonstrates that the diffraction efficiency of the improved Roman encoding is 2 times as much as that of the Burch encoding. Therefore, using the improved Roman encoding can achieve higher diffraction efficiency.
Infrared Technology
Infrared simulation of Kelvin wake on sea surface under different conditions
Wang Jiaolong, Zhang Haochun, Ma Rui, Wei Yanqiang, Ma Chao
2016, 37(6): 924-931. doi: 10.5768/JAO201637.0606001
The wakes generated by ships on the sea contain a wide range of information. We applied the Kelvin wake model and obtained the wake maximum wave height of 0.5 m, 1.5 m and 2.5 m,respectively, corresponding to the warships velocity of 5 m/s, 10 m/s and 15 m/s. We described the complex sea backgrounds with different wind speeds of 5 m/s, 8 m/s and 10 m/s by the PiersonMoscowitz sea spectrum model. The infrared emission model of the wake on the sea was established by geometry differences of the wake and the background, and infrared images were got in different speeds of the sea wind, different speeds of the ship and different detection angles of the detector. The simulation results show that the maximum gray value of infrared image is at the wake wave peak, and when the wind speed increases from 5 m/s to 10 m/s, the average gray difference between the wake area and sea surface background gradually reduces from 100, until no difference. Under the same sea surface wind speed, the wake wavelength increases from 10 m to 40 m with the ship speed increasing from 5 m/s to 15 m/s,and the infrared feature is obvious.The infrared image difference is insignificant when the detector zenith angle is 0 and 30. When the zenith angle increases to 60, the wake region gray scale is closed to the sea background gray scale, the difference value is less than 30, so it becomes more difficult to recognize targets.
MRTD in multispectral infrared imaging system based on AOTF
Zhang Yan, Wang Xiaobing, Geng Shunshan, Zhu Jiayi, Xu Aidong
2016, 37(6): 932-937. doi: 10.5768/JAO201637.0606002
In order to achieve the spectral minimum resolvable temperature difference (MRTD) testing of infrared multispectral imaging and obtain more information of target and background, an acoustooptic tunable filter (AOTF)based multispectral static performance testing platform was designed and developed. At 3 m~5 m waveband,through adopting the designed optical testing platform,the subdivision of band was carried out in middlewave infrared region,and the MRTD tests were finished in targets with different spatial frequencies of 2.546 lp/mm,1.273 lp/mm,0.849 lp/mm and 0.632 lp/mm,respectively. The experimental result shows that, the test results of spectral MRTD correspond with the theoretic analysis,verifying the reliability of the optical testing platform and the feasibility of the testing method.
Fiber Sensing and Optical Communication
Space laser communication system based on fiber laser phased array
Bi Mingzhe, Su Yuwei, Ma Wanzhuo, Liu Xianzhu, Ci Mingru, Jia Qingsong, Wang Tianshu, Liu Jingjiao
2016, 37(6): 938-941. doi: 10.5768/JAO201637.0608001
In order to meet the needs of the ultralong range and high speed space laser communication, a kind of communication system with the emitter utilizing a 4beam fiber laser phased array operating at 1.06 m was designed. The seed and one of the 4 beams were modulated, respectively, and the modulation rates of the pseudorandom sequence were 53 Mb/s, 120 Mb/s and 155 Mb/s. The results show that the quality of the receiving eye diagrams quality is better with the seed directly modulation at the same rates, and the receiving eye diagrams can be further improved through controlling the phases of the beam array. In the experiment, the multicarrier characteristics of the phased array modulated respectively at 2 beams were studied. The 5/5.08 MHz and 20/40 MHz sine waves were used as the modulation signals, respectively, and the frequency domain signal can be observed at the receiving terminal after beam combination and phase controlling. Therefore, the space communication system feasibility based on the fiber laser phased array can be verified in the experiment.
Demodulation system of fiber Bragg grating sensor based on FPGA
Yan Pengfei, Gao Qiang, Qiu Junpeng, Zhang Jianxiang, Zhang Baocheng, Yan Hongwei
2016, 37(6): 942-947. doi: 10.5768/JAO201637.0608002
In view of the present existing problems of fiber grating sensor demodulation equipment, a portable sensor demodulation equipment with lower cost and stable performance was studied and designed. The linear charge coupled device (CCD) spectral imaging method with high integration and strong adaptability to environment was selected to be the overall plan for demodulation equipment. The sensor demodulation system was established with the SOPC as the embedded demodulation kernel. And the experiments were carried out and results prove that the Gaussian fitting algorithm and spectrum correlation algorithm can get high demodulation accuracies, the average bias is within 0.005 0 nm,that is, 0.003 0 nm and 0.004 8 nm,respectively, the center wavelength demodulation of fiber bragging sensor resolution is effectively improved;moreover,the fiber grating sensor demodulation system based on field programmable gate array (FPGA) can satisfy the requirements of high integration and high resolution for demodulation system.
Research on dead zone of closedloop fiber optic gyroscope and optic power crosstalk error
Zhou Yuan, Sun Fengyuan, Liang Yong, Lyu Hangwei
2016, 37(6): 948-953. doi: 10.5768/JAO201637.0608003
The dead zone has severely influenced the application of the digital closedloop fiber optic gyroscope (DCFOG) in high performance inertial navigation system. A mathematic model focusing on feedback related interence was established to analyze the dead zone in fiber optic gyroscope and was verified through FOG dead zone measurement of its simulation data by simulink. Based on this,an optical power interference model was proposed, and the frequency characteristic of the interference source analyzed and compared to the optic power affected. Further, an interfer suppressed PCB layout shows a much less coupling and dead zone. All measurement shows that the feedback phase step signal dependent error is the primary cause of the dead zone;besides the electric crosstalk,the phase step dependent modulation of optic power can also bring error to gyro signal processing and cause dead zone. After the targeted design of decoupling and error modulation, the dead band reduces from 0.2/h to 0.02/h, which meets the requirements of the application.
Extrinsic F-P fiber optic sensor design for partial discharge detection and sensitivity analysis
Nie Dexin, Chen Liankai, Jiang Guoyi, Liu Haibo, Pi Benxi, Zhang Weichao, Liu Jie, Zhang Luan
2016, 37(6): 954-960. doi: 10.5768/JAO201637.0608004
To solve the problem of low sensitivity when using ultrasonic wave method to detect partial discharge (PD) in power equipment, a dielectric fiber FabryPerot (FP) acoustic sensor with quartz membrane was designed. For suitable frequency response characteristics of FP sensor, the natural frequency of FP sensor changed with diaphragm size was analyzed based on the theory of elasticity, and 3 FP sensors with different sizes were designed using ANSYS finite element analysis method. The ultrasound waves from 50 kHz to 250 kHz were generated from piezoelectric transducer (PZT) driven by signal generator in insulating oil tank. The ultrasound waves were detected by 3 FP sensors to get the amplitudefrequency characteristic curves. The experiment of plateplate PD detection by FP1~FP3 shows that the FP sensors with the first natural frequency of 150kHz could detect PD signals effectively, and the sensitivity can be significantly enhanced with the decreasing diaphragm thickness under the same natural frequency. The FP sensor sensitivity with the cavity length of 130 m is 2.47 times of that of the FP sensor with 100 m cavity length. The results show that the PD detection sensitivity of FP sensor can be enhanced by increasing the FP cavity length.