2015 Vol. 44, No. 8

Laser technology and application
Fabrication of high beam quality missile-borne active imaging laser
Mao Xiaojie, Bi Guojiang, Pang Qingsheng, Zou Yue
2015, 44(8): 2239-2242.
[Abstract](635) [PDF 1262KB](767)
The missile-borne laser active imaging guidance technology is one of the most important laser guidance technology in the modern war. Among them,the development of the missile-borne active imaging laser is current research hotspot and difficulty. A high beam quality laser of 1 064 nm used in laser missile-borne active imaging was reported. The pulse width of 3.005 ns,the pulse energy of 3.36 mJ and the spectral width of 78 pm at the repetition rate of 100 Hz were obtained by diode in-band end-pumped Nd:YAG crystal and integrated design. The quality of laser beam M2 is 1.327 in X direction and 1.354 in Y direction through in-band pumping and cavity optimization design. Imaging results show that, the successful development of the laser have directive meanings for the parameter design of high beam quality solid state laser and engineering application of laser active imaging.
Simulation of micro-groove cross-section in femtosecond laser ablation of quartz glass
Wu Dongjiang, Zhou Siyu, Yao Longyuan, Ma Guangyi, Zhuang Juan
2015, 44(8): 2243-2249.
[Abstract](880) [PDF 1339KB](1193)
The cross-section shape simulation model of micro-groove in femtosecond laser ablation of quartz glass was built based on the ablation rate model of transparent dielectric. Besides, the model was verified by ablation experiment. The effect of pulse energy and scan speed on the cross-section shape of micro-groove was analyzed to achieve the adjustment method of micro-groove shape. The analysis of simulation results shows that the depth and sidewall angle of micro-groove can be improved by decreasing the spot radius, increasing the pulse energy or slowing the scan speed. The width of micro-groove be improved by increasing the pulse energy or slowing the scan speed, but with the increasing of spot radius, it first increases and then decreases. The width of micro-groove reaches a maximum of 8.13 m at the spot radius of 13 m with the pulse of 4 J and the scan speed of 0.2 mm/s.
Study on thermal effect of LD end-pumped separated amplifier structure
Zhang Deping, Wu Chao, Zhang Rongzhu, Sun Nianchun
2015, 44(8): 2250-2255.
[Abstract](380) [PDF 1657KB](348)
The thermal effect of LD end-pumped rectangular separated laser amplifying medium was analyzed and studied. Thermal conduction model of Cr,Yb:YAG/Yb:YAG composite structure was established. The temperature distribution inside the medium was calculated by utilizing the finite element method. The computing method of the medium refractive index vary with temperature was given, and worked out the output end face wave front phase distribution change with temperature. The results reveal that, while the pump power density is unchanged, with different pumping time the temperature distribution and refractive index at the direction of the optical section are different. With the increasing of the pumping time, the temperature and refractive index also increases, the output end face wave front phase distortion enlarge as well. While the pump power density increases, the variation tendency of temperature and refractive index are similar to the situation while the pumping time changes. The thermal effect becomes more serious as the growths of pumping time and the increases of pump power density.
Influence of noise on range error for satellite laser altimeter
Zhou Hui, Li Song, Wang Liangxun, Zheng Guoxing
2015, 44(8): 2256-2261.
[Abstract](370) [PDF 1238KB](423)
Noise is an important factor of affecting range error for satellite laser altimeter with recording waveform. According to the distribution characteristic of received pulse signal and noise, the theoretical expression form about variance of time-centroid for received pulse signal was deduced. Thereby, the impact model of noise on range error was built-up. Base on the principle of minimizing range error, an optimization design method for low-pass filter was put forward. In terms of basic measurement parameters for Geoscience Laser Altimeter System(GLAS), the distribution regularities of range error and RMS pulse width for low-pass filter were simulated. As for linear target of geometrical parameters within 40 slope angle and 15 m roughness, the extent of range error is 0.28-32.49 cm. Correspondingly, the scope of RMS pulse width for low-pass filter is 1.4-57.4 ns. Aimed at targets with scope of 1 slope angle, the computed value of low-pass filter for GLAS is 2.2 ns, which is close approximate to 2 ns as published practically value. Meanwhile, on basis of optimizational results for low-pass filter, the range errors decrease significantly. The maximum of range error is decreased to 10.93 cm and corresponding reduction level gets 3 times. All the results show that impact model of noise on range error and optimization design method for low-pass filter is correct. They provide practical application values for hardware design and performance assessment of satellite laser altimeter.
Full-waveform LiDAR data decomposition method based on global convergent LM
Li Pengcheng, Xu Qing, Xing Shuai, Liu Zhiqing, Geng Xun, Hou Xiaofen, Zhang Junjun
2015, 44(8): 2262-2267.
[Abstract](631) [PDF 2332KB](907)
Full-waveform LiDAR is a rising technique in the field of remote sensing. Compared with traditional LiDAR, it can digitize all the back-scattering pulses. More abundant attribute of targets shall be obtained by waveform decomposition, which is the core content of full-waveform lidar data processing. A waveform decomposition method based on global convergent LM was proposed. Waveform was fitted and optimal solutions of components' parameters were obtained by introducing global convergent LM. Decomposition of complex overlapping waveform components was realized by iterative peaks detection. The experimental results on GLAS, LVIS and Lite Mapper-5600 waveform data prove that, the decomposing results are more robust than traditional LM and proposed method is practical as it is suitable for satellite, airborne large footprint size and airborne small footprint size waveform data.
Stealth technology of optical-electro imaging devices based on focal shift
Zhang Yufa, Sun Xiaoquan, Lei Peng, Yu Dabin
2015, 44(8): 2268-2273.
[Abstract](395) [PDF 1625KB](279)
Electro-optical devices can easily be captured by active laser detection weapons according to the Cat-eye effect of optical windows. The focal shift method was proposed to decrease retroreflected wave power for Cat-eye target stealth when the image quality of these devices was under controlled. The principle of focal shift was analyzed and experimental validation was carried out respectively. Furthermore, digital image of focal shift device was evaluated based on gray gradient function, and the blurred images were restored. The results show that the divergent angle of reflected wave is enlarged and retroreflected wave power decreased when the focal shift distance increases. Meanwhile, high-frequency information of images captured by focal shift electro-optical devices decrease accordingly. However, the deteriorative range of image quality is acceptable. After restoration, the visual effects of the images are improved efficiently.
Study on compound technology of laser shock peening and aluminizing improve the mechanical properties of K417 alloy
Jiao Yang, He Weifeng, Sun Ling, Zhou Liucheng, Nie Xiangfan, Luo Sihai, Li Jing
2015, 44(8): 2274-2279.
[Abstract](492) [PDF 1586KB](375)
Vibration fatigue tests were performed on aluminizing, LSP after aluminizing、aluminizing after LSP K417 alloy specimen respectively. The results showed that, compared with that treated by aluminizing only, the fatigue strength of specimen treated by aluminizing after LSP was improved by 50%and that treated by LSP after aluminizing was improved by 30%. It showed that the composite technology of LSP and aluminizing can improve the fatigue performance, and the composite technology of aluminizing after LSP can improve more effectively. The influence of different technology order to mechanical properties were investigated by X-ray diffraction(XRD), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The improvement mechanism of the fatigue performance was discussed. The results indicate that the LSP can promote the process of aluminizing. The combination of aluminizing layer with matrix is more close and a large number of columnar crystals formed in the surface treated by aluminizing after LSP, which lead to the thickness of aluminizing layer increase, and then the fatigue performance improved. But the LSP after aluminizing only affects the surface strengthening, and the improvement of fatigue performance is limited.
Experimental researches on acousto-optic Q-switched CO2 laser
He Yang, Lu Jun, Chen Fei, Li Dianjun, Zheng Changbin, Xie Jijiang, Guo Jin
2015, 44(8): 2280-2285.
[Abstract](430) [PDF 1683KB](216)
In order to meet the demand of 13.5-nm extreme ultraviolet lithography (EUVL), an acousto-optically Q-switched CO2 laser was developed, which has high repetition rate and high stability. First, the operating principle of the acousto-optic Q-switch was analyzed and the relationship between the voltage of modulated signal and diffraction efficiency was researched experimentally. And then, by studying the influence of modulated signal duty cycle on pulse waveform, the appropriate duty cycle was chosen to eliminate the pulse tail. Under the conditions of different repetition rates, pulse duration, power and the pulse amplitude stability were measured and analyzed. Finally, the beam pointing stability of the laser was measured. Experimental results indicate that the range of pulse repetition rate can be adjusted from 1 kHz to 100 kHz. When the repetition rate is 1 kHz, the minimum pulse duration is 252 ns and the maximum peak power reaches 7 579 W. By designing the support frames mainly made of invar steel, the unstablity of pulse amplitude is less than 3% and the beam pointing stability is only 46.6 rad. This acousto-optic Q-switched CO2 laser is suitable for a seed source used in EUVL.
Estimation of far-field divergence of high power TEA CO2 laser
Zhang Kuo, Lu Jun, Yang Guilong, Chen Fei, Li Dianjun, Zheng Changbin, Guo Jin
2015, 44(8): 2286-2291.
[Abstract](556) [PDF 1322KB](133)
In the application of high-power laser long distance transmission, the far-field divergence is the one of important parameters to evaluate the laser performance. Conventional methods cannot be used to measure the far field divergence precisely because of the unique characteristics of TEA CO2 laser, such as high average power, high peak power and large beam size. In order to solve this problem, a fitting analysis method was proposed to estimate the far field divergence of high power TEA CO2 laser. Firstly, the far-field divergence of multimode Gaussian laser with large Fresnel number was calculated theoretically. Then, the near-field beam size(20 m) was measured experimentally using a spot ablated method, and the beam quality and waist radius were calculated based on the M2 factor, and furthermore the far-field divergence was deduced. Finally, the results of these two methods were compared, and the deviation between the results was also discussed. It is indicated that the fitting method based on the experimental data is available to accurately evaluate the far-field beam divergence of high power TEA CO2 laser.
Infrared technology and application
Analysis of the effects of fill factor on image quality of micro-scanning system
Shen Tongsheng, Shi Haoran, Lou Shuli, Li Zhaolong
2015, 44(8): 2292-2297.
[Abstract](365) [PDF 1359KB](209)
Fill factor is an important parameter for the design of detector arrays, and it's necessary to research fill factor influence on image quality of micro-scanning system. One model of micro-scanning (22) as an example, on the basis of the detailed analysis of micro-scanning can reduce aliasing which is created by detector due to under sampling, output images were simulated with the case of different fill factors. Quantitative analysis on the simulation images from the perspective of image quality assessment was based on structure similarity. The simulation results show that the increase of fill factor can reduce aliasing effect and improve the quality of imaging. Pointed out that fill factor of detector can improve the quality of the image, but the influence on image quality is limited and degree on the improvement of the image was not large, which provide the theoretical and applied research for the design of micro-scanning imaging system.
Preparation and characterization of water-based infrared camouflage coatings
Cheng Shengyue, Liu Zhaohui, Ye Shengtian, Wang fei, Jia Yifan, Ban Guodong
2015, 44(8): 2298-2304.
[Abstract](520) [PDF 1532KB](201)
In order to investigate the use of water-based infrared camouflage coatings on tarpaulin, coatings with different infrared emissivities(0.589, 0.761 and 0.953) and different colors(khaki, emerald and dark green) were developed from fillers and auxiliaries; UV-Vis-NIR spectrophotometer, infrared thermal imager, SEM, and TG-DTG were used to characterize the performances of infrared camouflage coatings such as visible light-near infrared stealth, infrared stealth, surface topography, heat stability etc. The research results show that the visible light-near infrared reflectance spectra of infrared camouflage tarpaulin are similar with the background, the partition effectiveness of infrared map is good, and the usage requirements are met by the performances of the surface topography, heat stability and flexibility.
Spectroscopic characteristics of GaAs/Al0.3Ga0.7As quantum well infrared photodetectors
Hu Xiaoying, Liu Weiguo, Duan Cunli, Cai Changlong, Guan Xiao
2015, 44(8): 2305-2308.
[Abstract](444) [PDF 1178KB](176)
The method of metal chemical vapor deposition(MOVCD) was used to grow the GaAs/Al0.3Ga0.7As quantum well infrared photodetectors(QWIPs). The two sample-devices had large surface area 300 m300 m. But its pressure welding area of electrode in was 20 m20 m while that of the one out was 80 m80 m. Their spectroscopic characteristics were measured at 77K by use of Fourier Transform Spectrometer. The results show that the peak wavelength of 1# and 2# are 8.43 m and 8.32 m respectively. While the theoretical one is 8.5m according to Schrodinger equation. Thus the error between the experimental value and theoretical one of 1# and 2# are 1% and 2.1% respectively. Simulations demonstrate that metal chemical vapor deposition can satisfy quantum well infrared photodetectors processing needs and the different pressure welding area and position of electrode may has no influence on peak wavelength but has some influence on peak photocurrent.
Middle infrared colorimetric temperature measurement method considered influence of atmosphere and ambient
Lv You, Yang Bo, Wei Zhonghui, He Xin, Chang Songtao, Sun Zhiyuan
2015, 44(8): 2309-2314.
[Abstract](383) [PDF 1250KB](176)
Traditional colorimetric temperature measurement method commonly used in visible and near infrared band, can only get high precisions when measuring near high temperature target, and can't get high precisions when measuring far low-middle temperature target. Aimed at the limitations of traditional method, infrared colorimetric temperature measurement method was put forward considering atmosphere and ambient radiance, an colorimetric temperature measurement system based on middle infrared camera was established. First, standard blackbody was used for calibration of middle infrared camera and single-band of colorimetric system; then colorimetric temperature measurement model with ambient radiance parameter was deduced, a new function between ratio of two radiances and temperature of target was established; finally, measurement temperature of home-made gray-body in the laboratory was made, the feasibility of proposed method was verified. Experiments show that: in the experimental temperature range, absolute error of temperature measurement is less than 4 ℃, the temperature relative error is less than 6.7%, the measurement accuracy of radiation intensity is higher than 10%. The colorimetric temperature measurement method considering atmosphere and ambient is greatly superior to traditional method.
Key subjects of UCIR guidance applied on air defence
Yin shengli, Pan Hongtao, Wang Zichen, Wu Zepeng
2015, 44(8): 2315-2320.
[Abstract](788) [PDF 1227KB](1187)
For the recent progress in semiconductor, and the development in sensitivity of uncooled infrared imaging device, uncooled IR seeker is applied on the air- to-surface missile, but none of surface-to-air. Because of its short flying time and a nearer distance, uncooled IR seeker is used on Terminal Defence Misslie. Also there are some practical points needing to be researched in deep. There are some key points on the air-to-surface like anti-aircraft. First of all, the different bands it works lead to a different target or background characteristics, affecting the acquired distance; There is a longer integration time constant of uncooled IR detector compared with the cooled, it is hard to track high maneuvering targets; Finally, the aerodynamic heating on the seeker dome will cause severe thermal radiation effect on the detection system in the aerodynamic thermal environment, because of the long-wave IR band and the long time flying. If such problem can be solved favorably, uncooled IR seeker will be applied quickly on Terminal Defence Misslie, and this research will provide a reference.
Analysis of the influence of infrared temperature measurement based on reflected temperature compensation and incidence temperature compensation
Shi Dongping, Wu Chao, Li Zijun, Pan Wei
2015, 44(8): 2321-2326.
[Abstract](414) [PDF 1893KB](470)
Based on the basic theory of infrared radiation and principles of temperature measurement using infrared imager, two methods of temperature compensation were proposed, reflected temperature compensation and incidence temperature compensation, in order to ensure environmental temperature object has less of an effect on infrared measurement. The theoretical analysis proved its feasibility and the operation program was put forward and used in production. The compensation measurements were demonstrated in a laboratory experiment with four sulfide ore samples. The results show that the fitting of compensation measurement with true temperature is better than that of common infrared measurement. The fractional error of reflected compensation measurement significantly is less than the incidence. The theoretical analysis and experiment result indicate the feasibility of the proposed methods. The compensation measurements ensure the measurement accuracy as well as expand the scope of common thermal infrared imager application and ensure the numerical accuracy of infrared prediction in the spontaneous combustion of sulfide ores.
Construction of Malkmus statistical narrow spectral band model parameters database based on HITEMP2010
Chen Shiguo, Chen Lihai, Mo Dongla, Shi Jingcheng, Mei Fei
2015, 44(8): 2327-2333.
[Abstract](520) [PDF 1376KB](152)
In order to make high accuracy predictions of high temperature combustion gases infrared radiation characteristics, the spectral band model parameters such as spectral absorption coefficient or spectral transmittance which changed with gases temperature and wave number must be invoked. A new construction method of spectral band model parameters database based on Malkmus statistical narrow band model was proposed. The HITRAN2008 and HITEMP2010 molecular spectroscopic databases were employed to meet the requirement of normal temperature and high temperature calculations in the mode, and a calculation program for the Malkmus statistical narrow band model with average transmittance had been developed. Then the program was employed to calculate the single component spectral radiation characteristics of CO2 and H2O in both homogeneous path and inhomogeneous path respectively, and the multi-component spectral radiation characteristics of CO2, H2O and N2 in inhomogeneous path. The result shows good agreement with the experimental data from the literature, and the proposed Malkmus statistical narrow band model is suitable for the high temperature gas radiation transfer characteristic calculation.
Efficiency of aero-engine infrared radiation computation by using BMC method
Huang Wei, Ji Honghu
2015, 44(8): 2334-2338.
[Abstract](430) [PDF 1175KB](155)
The Backward Monte Carlo (BMC) method is a common method for calculating the target's infrared radiation signature because of its high accuracy and strong adaptability. Based on general CFD/IR numerical calculation method, the impact of ray discrete step size, ray number, energy carrying method on aero-engine infrared radiation intensity computation efficiency was investigated by using BMC method. The results show that the computation efficiency is high when the ratio of ray discrete step size to equivalent diameter of nozzle exit is between 0.05 to 0.1 and ray's number is more than 105; the computation time can be shortened by dozens of times through ray carrying multiple bands energy method; the computation time of BMC method can be reduced further by parallel computation with MPI platform, but the parallel efficiently will be decreased with increasing the computation core number. In the premise of ensuring the accuracy of the results, the efficiency of infrared radiation computation was improved by reasonable selection of parameters, algorithm improvement and parallel computation.
A combined non-uniformity correction algorithm of IR staring imaging system
Nie Ruijie, Li Lijuan, Wang Chaolin, Xu Yanke
2015, 44(8): 2339-2346.
[Abstract](473) [PDF 1490KB](509)
With the development of IRFPA techniques, IR staring imaging system has been applied in more and more fields. In these applications, the residual non-uniformity and the non-uniformity correction(NUC) algorithms of the output IR images are of major concern. In order to resolve this problem, the non- uniformity sources and their characteristics in spatial frequency domain were studied firstly in this paper, and then the advantages and the disadvantages of both Calibration-based and Scene-based NUC algorithms were taken into account, and finally a combined non-uniformity correction algorithm including Blind-pixel Detection and Compensation was put forward to implement the non-uniformity correction, and the experiments results were given as well. The results shows that the combined non-uniformity correction algorithm can prevent the RNU to increase with the changes of time and working environments well, and has excellent performances in NUC technical applications.
Analysis and processing of infrared dual waveband radiation ratio based point target
Wang Wenbo, Wang Yingrui
2015, 44(8): 2347-2350.
[Abstract](322) [PDF 1805KB](163)
Infrared dual waveband radiation ratio can denote the blackbody's temperature information, and can be used for temperature measurement. When using infrared dual waveband radiation ratio to measure the temperature of point target, it is difficult to achieve high-accuracy because of various kinds of noises. The recurrence plot theory was used to analyze the non-station of infrared dual waveband radiation ratio. According to the non-station of infrared dual waveband radiation ratio, the target's response signal in IR single waveband was processed by moving average filter. The IR dual waveband radiation ratio was processed by wavelet soft-threshold filter. Experimental result indicate that, when the SNR12, 1 K temperature accuracy can be achieved with above processing method for static point target, and 2 K temperature accuracy can be achieved for slow moving point target.
Optoelectronic measurement
Robot kinematic parameters compensation by measuring distance error using laser tracker system
Du Liang, Zhang Tie, Dai Xiaoliang
2015, 44(8): 2351-2357.
[Abstract](410) [PDF 1274KB](181)
The robot position accuracy is measuring the robot pose error between the command distance and the actual distance. To improve the robot accuracy, it needs to compensate on robot kinematic parameters. Laser tracker was used to measure the robot distance error in this article. The mapping between the actual kinematic parameters and the robot distance error model was obtained. Some kinematic parameters in modified D-H kinematic model that Hayati proposed can not be identified, therefore, the condition number was introduced to identify the distance error matrix. Through computing the condition number, the unidentified kinematic parameters in distance error kinematic model was deleted. Ultimately, the robot kinematic model using the identified kinematic parameters was compensated. It improves the robot accuracy apparently.
Design of laser triangulation system based on synchronized scanners with LIDAR
Fei Kai, Zhang Lu, Zhu Feihu, Zhang Xu, Tu Dawei
2015, 44(8): 2358-2363.
[Abstract](400) [PDF 1577KB](154)
In order to realize the three-dimensional measurement of the objects regardless of far or near and expand the measurement range, a laser triangulation system based on synchronized scanners with LIDAR was established. Its principle, design and device selection were investigated. First, according to the synchronous scanning mechanism, the LIDAR technology was fused based on traditional three-dimensional measurement and the computational formula of the 3-D points was deduced. The selections of laser device, lens, and dichroscope, scanning servo motor, LIDAR acceptor and camera were analyzed based on system design requirement. After that the mechanical structure was designed and the light path of optical system was simulated by Zemax to prove the feasibility of principle. Finally, the back of light of APD was tested and the actual object was scanned to acquire 3-D point clouds. The experimental results show that the system is feasible.
Error analysis of space analytic geometry method for celestial position and orientation determination
Wang Haojing, Wang Jianli, Wu Liang, Yang Qingyun, Wang Minghao
2015, 44(8): 2364-2374.
[Abstract](380) [PDF 1904KB](352)
In order to determine the influence of each error source on position and orientation determination error for three-field position and orientation device, the error analysis model of system was established. Firstly, the principle of three-field position and orientation device using space analytic geometry method was proposed, and the various error sources which affected accuracy of position and orientation was pointed out. Secondly, the characteristic and the probability distribution of error source were summarized; and the impact of error sources on position and orientation information pair was assessed. Then, the position and orientation error analysis model was established by using the homogeneous coordinate transformation matrix and principle of navigation. Finally, the error simulation was analyzed by using Monte Carlo method. The simulation results show that mean of position fix error is 121.0 m, mean of orientation fix error is 7.4, and it is pointed out that dominant error source is horizontal measurement error, followed by data error of deviation of vertical. Field experiments show that the mean of position fix error is 182.12 m; mean of orientation fix error is 9.3, and it is demonstrated that horizontal measurement error has the main influence on the overall outcome.
Impact of dark current on SWIR polarimetry accuracy Hu Yadong, Hu Qiaoyun, Sun Bin, Wang Yi, Hong Jin
Hu Yadong, Hu Qiaoyun, Sun Bin, Wang Yi, Hong Jin
2015, 44(8): 2375-2381.
[Abstract](422) [PDF 1189KB](164)
The variation of dark current is the key factor influencing the accuracy of the signals of detectors in the short-wave infrared(SWIR) band. Firstly, based on the analysis of the working principle of infrared detector G5853-21, an experiment was designed aiming to find the relation between dark current, temperature and reverse bias of the detector. Also, an error model was given for the infrared polarimeter by considering the influences of dark currents. Error models for Stokes parameters and the degree of polarization have been built for the polarimeter. Allowing for the specific conditions in the space environment,an optimization was designed to reduce the impacts of dark currents and temperature requirement was also given for the infrared polarimeter. The results indicated that, with accurate control of the temperature, the error of the degree of polarization, involving the measurement uncertainity and other noises, could be below 0.42%(with =0.3).
Thermal effect model analysis and dynamic error compensation of industrial robot
Li Rui, Zhao Yang
2015, 44(8): 2382-2388.
[Abstract](510) [PDF 1535KB](428)
To advance the precision of the robot motion is one significant research goal of robot flexible processing issues. In the process, deformation mechanism of heat caused by temperature variation is found as one of the important reasons for affect the positioning error. The temperature compensation method suitable for the industry field was presented and testified through this paper. Effect of robot self-heating and scene environmental temperature factors on axial motion and the ending actuator positioning accuracy were analyzed. The thermal distribution and deformation models were built using finite element theory. Thermal compensation strategy was presented to accomplish the experimental and theoretical analysis of significant correlation between robot kinematics parameters and thermal models above, especially self-heating effect. It was convenient and suitable for industrial field environment. Thermal compensation is experimentally proved to carry the ability to adjust the position error of ending actuator to less than 0.1 mm.
High-speed focusing technique for lithography based on line scan CCD
Chen Changlong, Di Chengliang, Tang Xiaoping, Hu song
2015, 44(8): 2389-2394.
[Abstract](393) [PDF 1377KB](445)
With the improvement of lithograph resolution, the depth of focus (DOF) of lithographic projection objective is decreasing. In order to take full advantages of the restricted DOF, focusing is commonly used to adjust the wafer onto the ideal focal plane. As the key point of focusing, research on focus detection becomes very popular. The present focus method is based on four-quadrant detector or array CCD to grab light signal, which carries the defocusing amount information of the wafer, and then process image on computer. This method is slow and cannot satisfy the real-time requirement for focusing. Therefore, a focus detection method, which wass based on line scan CCD for image grabbing and FPGA for image processing, was provided. This method can detect the defocusing amount in high-speed by utilizing the high-speed of line scan CCD and FPGA's parallelism, combining with sub-pixel boundary detection algorithm based on polynomial interpolation. In order to compensate the defocusing amount, FPGA directly control the motor to drive the wafer stage up and down, making the focusing system a real-time closed loop. Due to reducing the computer links, this design has high-speed, high-resolution, low power consumption and low-cost characters.
Application of improved particle-swarm-optimization in stabilized platform based on multiple reference frame model
Fan Xinming, Cao Jianzhong, Yang Hongtao, Wang Huawei, Yang Lei, Liao Jiawen, Wang Hua, Lei Yangjie
2015, 44(8): 2395-2400.
[Abstract](451) [PDF 2385KB](134)
In the conventional servo system, model analysis according to motor axis and base space is used as a reference. However, when analyzing the stabilized platform, it is not compatible due to in which exists inertial space and base space. In order to solve this problem, the multiple reference frame model was proposed, where direct-current motor model was based on inertial space. On the basis of the multiple reference frame model, an improved Particle Swarm Optimization(PSO) algorithm was also proposed. As a kind of swarm intelligence algorithm, PSO was widely used in parameters optimization. The traditional PSO on inertial weight and slopping-over borders were improved, and then, it was adopted in tuning and optimization of PID parameters. The simulation and experiments results indicate that the improved PSO(IPSO) PID controller can obviously enhance the static precision and effectively isolate the vibration and disturbance of carrier.
Calibration method of on-orbit attitude systematic error for space-borne laser altimeter of earth observation
Ma Yue, Yang Fanlin, Yi Hong, Li Song
2015, 44(8): 2401-2405.
[Abstract](310) [PDF 1375KB](202)
The range between satellite and surface target was acquired by processing the weak received waveform which was transmitted from the space-borne laser altimeter and reflected by earth surface. Combined with the precise orbit and attitude data, the accurate location and elevation of laser footprint were calculated. As for the altimeter with elevation accuracy of 10 cm magnitude, the systematic error on attitude angles influencing the accuracy severely should be calibrated effectively. The analytic model of attitude angle error associated with priori knowledge of earth surface was deduced, and the calibration method used to eliminate the attitude error was designed, which utilized the ocean surface as calibration field, was by way of satellite attitude maneuver and based on least squares estimation algorithm. The results of simulation show that the designed method can estimate the systematic error precisely and effectively, even if the mass observed data were lost, the estimated bias is less than 5%. This on-orbit calibration method is beneficial to the systematic error correction for the space-borne laser altimeter, and is of reference significance.
Compensation and identification of non-common path error in lateral shearing interferometry
Liu Bingcai, Li Bing, Tian Ailing, Gao Fen
2015, 44(8): 2406-2410.
[Abstract](511) [PDF 1478KB](189)
Because standard reference wave-front is not needed in lateral shearing interferometry(LSI), interferometry cavity can be shorten, even absolute common path interferometry could be achieved, and it is immunity to air turbulence and vibration. Therefore, non-common path error between two shearing wave-fronts which come through different cubic prisms, shear plate and pentaprism is not avoided. In this paper, calculation method of non-common path error was proposed by contrast analysis between adjustment error and non-common path error in shearing interferometry, and non-common path error in surface measurement result was compensated. Lastly, experiment results demonstrate the surface result after compensation is in accordance with ZYGO interferometer.
Photoelectric device and material
Characteristics analysis and simulation of Fresnel concentrator in concentrated photovoltaic system
Zhang Mingjun, Gao Wenying, Niu Quanyun, Yuan Xingqi
2015, 44(8): 2411-2416.
[Abstract](497) [PDF 1366KB](136)
The concentrator in solar concentrated photovoltaic system was studied. The advantages of Fresnel lens for solar concentrator and its focusing characteristics and optical efficiency were analyzed, and the designing formula of point focus Fresnel lens with flat surface outward and Fresnel surface facing to the solar cell was obtained. Based on the theory of non-imaging optics, the ray trace simulation was realized in the non sequence model of ZEMAX software, and the solar energy distribution on focal plane of Fresnel lens for a certain size was analyzed and simulated. The simulation results show that, the solar energy of focused facula generated by usual Fresnel lens mainly focuses on the centre of the solar cell, and as the distance from the centre increases, the energy density of the concentric rings decreases. To make the solar energy distribution of the solar cell even, the second concentrator in concentrated Photovoltaic should be added.
Thermal performance testing for high power light-emitting diode based on voltage-current characteristics with pulse injection
Wang Xin, Xu Yingjie, Fan Xianguang, Wang Haitao, Wu Jinglin, Zuo Yong
2015, 44(8): 2417-2422.
[Abstract](296) [PDF 1400KB](158)
Thermal performance is one of the main factors which affect the optical and electrical performance of high power LED. The thermal performance testing system for high power LEDs based on voltage-current characteristics with pulse injection was designed in this paper, which can test the relationship between the operating current and forward voltage of LED under different junction temperatures, thereby obtaining LED thermal characteristics parameters. The system worked by generating a controlled narrow pulse current to drive the LED, and sampling the peaks of voltage and current of LEDs with LED heat sink temperature control and acquisition, thereby obtaining the voltage-current characteristic curve in different junction temperatures. Compared with other voltage-current testing systems, the designed system adapts the narrow pulse duty cycle(1 s), so the PN junction of LED devices is always in the process of alternately heating and cooling, which can avoid large heat accumulation and greatly improve the accuracy of measurement. In the experiment, a power LED device was tested by the system and the voltage-current-temperature curve was obtained. Then the B-spline based U-I-T model of the LED was established, so the real-time online detection of LED device was achieved.
Research of UWB multifunctional modulation based on phase modulator
Ma Xiaolu, Huang Shijie, Zhang Yi, Zhu Tianyang, Cao Fengjiao, Zhao Meng, Li Peili
2015, 44(8): 2423-2428.
[Abstract](348) [PDF 2656KB](139)
A UWB multi-functional modulator scheme based on cascade of phase modulation (PM) and filters was presented. This scheme was simple and could switch a variety of UWB modulation format flexibility by simple pre-coding to realize on-off keying(OOK), pulse bi-polar modulation(PBM), and pulse shape modulation(PSM). The generated three kinds of signal contained only a single wavelength, which can be transmitted over optical fiber without complex nonlinear control and dispersion management. By simulating through the software of Optisystem, the impact of light source power, modulation rate, and the system error of two PM modulators and filters on modulated signal was investigated. In addition, the transmission characteristics of modulated signals in single were also discussed. We found that the input power and modulation rate should between a certain range in order to get optimum UWB modulation signals.
Impact of dipole photoconductive antenna structure on the THz radiation characteristics
Xia Zuxue, Liu Falin, Chen Junxue, Shang Liping, Deng Hu, Xiong Liang
2015, 44(8): 2429-2434.
[Abstract](411) [PDF 1327KB](156)
Influence of the geometrical parameters of GaAs dipole photoconductive antenna(PCA) on the PCA's radiation characteristics was studied. At first, the analytical solution of PCA's current obtained by the Drude-Lorentz(DL) model was obtained as excitation, and the numerical finite-difference time-domain(FDTD) simulation was conducted. This had effectively solved the problem of analytical solution (where the relative intensity of THz radiation can be obtained by time derivative) which cannot simulate the influence of PCA structure parameters. Then, using the equivalent circuit model of dipole photoconductive antenna and the equivalent source resistance's expression, both the PCA's and the source's impedances were obtained for the practical PCAs. And it is demonstrated that the matching efficiency is not high because of the very low source impedance. Finally, by considering both the FDTD simulation results and theoretical calculation results, it can be proved that the dipole antenna's radiation efficiency will increase with the increase of its aspect ratio. This conclusion is found to be in accordance with the reported measured results. Thus the simulation results, the theoretical model and the calculation results are all verified.
Hot-pressed ZnS post-treatment modification and analysis of its high temperature properties
Gan Shuowen, Yang Yong, Lian Weiyan, Zhang Gaofeng, Shang Qinglin, Wang Yuezhong, Ma Jinpeng
2015, 44(8): 2435-2440.
[Abstract](426) [PDF 1429KB](188)
Zinc sulfide(ZnS) is an important infrared material because of its optical characters in 8-10 m. It is widely used in the area of missile dome, infrared astronomical satellite, infrared spectrometer, measure instrument and thermal imager. The high temperature treatment make hot-pressed ZnS crystal develop, therefore, hexagonal ZnS and crystal pores are eliminated in the polycrystal ZnS samples. The infrared transmittance is increased. The average transmittance of post-treatment ZnS sample is 73% in the range from 2 m to 10 m, and 60% at 1.064 m, with 5 mm in thickness. The thermal shock resistance test results that the post-treatment ZnS reserve mechanics characters of hot-pressed ZnS before, and it make optical-electro detecting system imaging clarity through post-treatment ZnS window at 400 ℃.
Structural design of 4 m telescope mount base based on topology optimization method
Fu Shixin, Zhou Chao, Cao Yuyan, Fan Lei, Han Xida
2015, 44(8): 2441-2447.
[Abstract](444) [PDF 1645KB](160)
To meet the requirement for high stiffness and lightweight, topology optimization method with constraints of static displacements and first resonance frequency was studied in 4 m telescope mount base design. Firstly, mathematical model of topology optimization was built subjected to minimum compliance, with pseudo density of the finite elements as design variables, static displacements, first resonance frequency and total mass as optimization constraints. Procedure of calculating sensitivities of optimization objective was presented in detail. Furthermore, topology optimization method was applied in mount base design, based on which shape and size design were carried out. Finally, the static stiffness and dynamic behavior of the optimized structure was analyzed and checked using the finite element method. The achieved results show that total mass of mount base reduces from 27.66 t to 22.15 t, while the maximum displacement decreases from 0.037 7 mm to 0.014 mm and first resonance frequency increases from 217.1 Hz to 247.45 Hz, ie, improving static and dynamic performances with lots of mass cut, which validate the presented topology optimization method. This topology optimization method will provide efficient help to other components' design of 4m telescope mount.
Effect of coupling strength on the phase locking performance of fiber lasers coupled with a common ring cavity
Lei Bing, Cao Jianqiu, Liu Wei, Hu Haojun, Feng Ying
2015, 44(8): 2448-2455.
[Abstract](404) [PDF 1510KB](140)
Passive phase locking of two fiber lasers which were coupled by a common ring cavity had been demonstrated, and the effect of coupling strength between them on the phase locking performance had been investigated in detail. The ring coupled cavity was chiefly composed of two 22 fiber couplers, which provided a common channel for mutual injection coupling and made the output phases of component lasers were primarily synchronized. The theoretical model of analyzing the effect of coupling strength was presented, which was based on the fact that the coupling strength between the fiber lasers was mainly determined by the coupling ratios of fiber couplers, and the effect of magnitude and difference of these coupling ratios on the circulating intensity in the common ring cavity and the output intensity of the phase locking array were investigated in theory. Moreover, efficient phase locking of two Erbium-doped fiber lasers with the common ring coupled cavity had been demonstrated, and the coherence of output lasers and their combining efficiency were also studied by analyzing the far-field interference pattern and output power of the array in experiment. The research results indicatd that adequate coupling strength was a necessary condition to achieve effective phase locking, and improving the coupling strength by increasing the coupling ratio can enhance the coherence of the phase locking array and decrease the combining efficiency slightly.
Advanced optics
Research of radiometric cross-calibration about GF-1 satellite sensors
Yang Lei, Fu Qiaoyan, Pan Zhiqiang, Zhang Xuewen, Han Qijin, Liu Li
2015, 44(8): 2456-2460.
[Abstract](351) [PDF 1722KB](169)
This paper is about the radiometric cross-calibration method of GF-1 image with landsat8-OLI data. First the cross-calibration was implemented using the night deep sea imaging to obtain the bias of GF-1 cross-calibration coefficient. Then eight times images of two sensors passing through the target place were selected to obtain the gains of the GF-1 cross-calibration coefficient. The correlation between the radiance value calculated by the cross-calibration coefficient and the synchronous observations of the Landsat8 radiance value is above 95%. The accuracy relative errors of the 4 bands are 4.25%, 6.21%, 5.83% and 5.66% respectively. The results show that the calibration coefficients obtained from the method have a similar precision as Landsat8-OLI. The calibration coefficients can satisfy the quantitative applications of GF-1 data.
Laser induced damage characteristics of nodules in thin-film polarizers
Tuniyazi Abudusalamu, Cheng Xinbin, Bao Ganghua, Jiao Hongfei, Wang Zhanshan
2015, 44(8): 2461-2466.
[Abstract](654) [PDF 1316KB](214)
In this paper the laser damage characteristics of nodule defects in 1 064 nm HfO2/SiO2 polarizers was discussed. To find the correlation between the seed diameter and the damage threshold of nodular defects in thin-film polarizers, monodisperse SiO2 microspheres were implanted on quartz substrates, and 1 064 nm HfO2/SiO2 polarizers were fabricated on quartz substrates by using electron beam evaporation deposition technique. The defect density of nodules that were created from SiO2 microspheres was purposely controlled to be around 20-40 mm2 and spin coating was taken to minimize clusters of SiO2 microspheres. To get the statistical value of ejection fluences of these engineered nodules, a raster scan damage test was used with a pulse width of 10 ns 1 064 nm laser. Laser damage test results showed that in thin-film polarizers the ejection fluences of nodules monotonically decrease with the increase of silica microsphere diameter.
Full parallax stereo holography research based on CGH
Yan Gaobin, Yu Jia, Liu Huiping, Kan Lingyan, Wang Jincheng
2015, 44(8): 2467-2471.
[Abstract](542) [PDF 1361KB](696)
A new method of making three-dimensional hologram by laser direct wrinting system was proposed, which was based on the principle of CGH and combined stereo holography. First, the experiment of fresnel computer generated hologram was conducted and the results demonstrated that it is feasible and rational to combine CGH with stereo holography. Then the three-dimensional model was sampled and the sampled image were processed by the principle of stereo holography and CGH. By digital holographic laser printing system, three-dimensional hologram was produced, which could be opticaly reproducted by laser, and the final results were analyzed and discussed.
Optical design of micro DLP projection based on novel light pipe
Wang Cheng, Hao Wenliang, Tian Liwei, Wang Ruofei, Zhu Xiangbing
2015, 44(8): 2472-2477.
[Abstract](616) [PDF 1673KB](226)
Traditional DLP technologies can not collect and utilize the light which is reflected by the micromirrors of DMD in the OFF state. Aiming at this defect, one design scheme of the micro DLP projection system based on a novel light pipe was presented. This system included LEDs, light pipe, color wheel, the collimation system and projection lens. A bending light pipe was added on the base of the tapered light pipe, and a compound parabolic concentrator(CPC) was used in the input end to collect the extra light reflected by the DMD. First, the related parameters of each part were analyzed and calculated according to the nonimaging optics theory. Second, the collimation system and projection lens were optimized by ZEMAX software. Finally, the model was built and simulated in TracePro software. The simulation results show that: with the number of micromirrors in the OFF state growing, the improving light efficiency ability of collecting light pipe first increases then decreases. Comparing with having no collecting light pipe, the light efficiency is increased by 5.33%; light pipe improves the most light efficiency, 5.91%, when half of the micromirrors are in the OFF state.
Analysis of attitude change impact on aerial push-broom imaging
Xian Guang, Yan Changxiang
2015, 44(8): 2478-2483.
[Abstract](357) [PDF 1579KB](146)
The shift generated from aircraft attitude change was one of the main factors affecting the optical imaging quality in aerial push-broom imaging,which could be compensated by stable platform. In this article,based on an particularly airborne imaging spectrometer system,firstly the precise image motion velocity model was established by the homogeneous coordinate transformation method, and the flight attitude accuracy required by the imaging quality was analyzed, thus the parameters of stable platform could be choosed correctly. Then the influence of the residual of compensation of attitude on the imaging quality was analyzed, obtaining the relative shift speed deviation was only 10-1, which providing references for the following spectral calibration and geometric correction. Again, to study the distribution of flight parameters of a given imaging requirement, the error analysis was carried out. Finally, the flight imaging test was carried out. The result showed that the selected PAV30 stable platform could ensure the demand of stability during imaging, which verifying the above analysis was correct and reasonable. The proposed method was simple and easy to implement, having a certain value in engineering.
Line-of-sight stabilization and modeling analysis of bias shafting mirror platform
Song Jiangpeng, Sun Guangli, Zhou Di, Li Dan
2015, 44(8): 2484-2490.
[Abstract](371) [PDF 1759KB](434)
The conventional mirror stabilized platform consists of two-axis azimuth-elevation gimbal axes and the sensor input Line-of-sight (LOS) is always oriented parallel to the outer gimbal axis. Compared with conventional mirror platform, the bias shafting mirror gimbal axis can have an arbitrary orientation with respect to the sensor LOS, and the resulting LOS kinematics are both axis-coupled and non-linear. The primary purpose of this paper is to study LOS kinematics and dynamic modeling of this bias shafting mirror. Firstly, the artificial mass stabilization platform method was proposed to derive LOS kinematics. Meanwhile, the artificial platform gimbal type was determined to derive equations of dynamics. And a complete dynamics model was presented based on LOS coordinate system. Then, the carrier motion coupling was analyzed and system control block diagrams were developed. Lastly, simulation results show that the characteristics of LOS pointing and torque coupling is different between the bias shafting and conventional mirror platform.
Design and fabrication of diamond/V2O5 films in continuous laser protection
Zuo Yangping, Lu Wenzhuang, Zhang Shengbin, Yu Yaping, Feng Sen, Zuo Dunwen
2015, 44(8): 2491-2495.
[Abstract](514) [PDF 1453KB](180)
In order to satisfy the requirements of infrared detector that can penetrate in visible and 3-5 m double wave bands, be reflected in 3 m wave band, optical diamond was selected as infrared window material to protect infrared detector from laser beams. V2O5 film with thermally induced phase transition properties was selected as anti-laser blinding coating. ZnS and YbF3 were chosen as high and low index of refraction materials respectively. Infrared anti-reflective coating applied on laser protection was designed based on design theory of films and optimized by TFCalc. Anti-reflective coatings were fabricated by ion assisted deposition and V2O5 coating was fabricated on anti-reflective coatings by using the method of magnetron sputtering. The surface topography and roughness of optical thin film were tested by scanning probe microscope and the infrared spectra was tested and analyzed. The results meet the requirements of design and application.
Optical communication and optical sensing
Simulation and analysis for indoor visible-light communication based on LED
Shen Zhenmin, Lan Tian, Wang Yun, Wang Longhui, Ni Guoqiang
2015, 44(8): 2496-2500.
[Abstract](436) [PDF 1617KB](225)
LED could be used for both the illumination and the wireless communication simultaneously that owns the modulation bandwidth from several MHz to several hundreds of MHz. The criterion of the minimum mean square deviation was used to design the layout of LED in the room. The indoor illumination distribution was analyzed in the two conditions which were respectively not included the wall reflection and included it. Then the illuminance, the received power for detector and the signal to noise ratio for the line of sight(not including the wall reflection) and the non line of sight(including the wall reflection) were analyzed, respectively. It is concluded that the illuminance and the received power are larger for the non line of sight than the line of sight, but the signal to noise ratio decreases. This is mainly caused by the inter symbol interference from the reflection of the wall of the non line of sight.
Design of off-axis optical antenna for space optical communications
Sun Quanshe, Zhao Facai, Chen Kunfeng, Han Zhong
2015, 44(8): 2501-2505.
[Abstract](340) [PDF 1922KB](272)
Space optical communications terminals frequently rely on optical telescopes to enhance the transmitted and received efficiency of the communication system. An optical design of a space laser communications optical antenna system was proposed to overcome the traditional on-axis Cassegrain optical antenna's disadvantages of small field of view and low emission efficiency. As an example, an optical antenna system operating at 0.85 m, 1.064 m and 1.55 m with aperture size 150 mm, magnification 15 was designed. The initial parameters were computed, and the ray tracing and optimization for the optical antenna system were performed with ZEMAX-EE software. The analysis results demonstrate that the Root Mean square(RMS) of a spot radius is less than 10 rad in the working wavelength(0.85 m, 1.064 m, 1.55 m), which implements astigmatism correction and obtains a good diffraction-limited quality in a wide spectral region and a high magnification. These results prove the feasibility of the optical design method proposed.
Performance evaluation of full-duplex free space laser communication system based on modulating retro-reflector
Zhang Peng, Wang Tianshu, Yang Guowei, Jia Qingsong, Ma Wanzhuo, Zhang Lizhong, Tong Shoufeng, Jiang Huilin
2015, 44(8): 2506-2510.
[Abstract](314) [PDF 1210KB](158)
Free space optical communication based on modulating retro-reflector(MRR) is research hotspots of future wireless optical communication because of less power, compact structure and without Acquisition, Pointing and Tracking (APT) requirement at system based on MRR. Full-duplex free space laser communication system based on MRR and double-wavelength laser is proposed. The link budget between small satellite under low orbit and ground station and bit error rate(BER) of optical communication are calculated when Communication distance and rate are 300 km and 1 GHz. It can be found that the link budge is more than 5 dB, and BER is less than 10-15. The results show that the budge and BER meet the communication requirement. Then limitation of the emulation is also analyzed. In conclusion, the proposed system can be used between light-weight full-duplex laser communication of small satellite under low orbit and ground station. It may be one of the future development trends of space optical communication system.
Theoretical and simulated research on bias points optimization of optical modulation of microwave signals on board satellite
Li Yongjun, Miao Xinping, Li Xuan, Zhao Shanghong, Li Ruixin, Liu Zhenxia
2015, 44(8): 2511-2516.
[Abstract](1207) [PDF 1538KB](14215)
Optical modulation theory of DE-MZM on board satellite was studied, output optics field expression of modulator with single input microwave signal was obtained. The analytical expression of four key parameters including carrier to noise ratio(CNR), RF gain, noise figure(NF), spurious-free dynamic range(SFDR) were deduced. The inter-satellite links transmission equation of microwave photonics was built. Using simulation software of OptiSystem, simulated model of microwave photonics links on board satellite was constructed and simulating research was performed. The simulated results show when the bias point is set to orthogonal bias point, RF gain is optimal. CNR, NF and SFDF are synchronously optimized when the modulator is low biased.
Spatially and spectrally resolved fiber mode measurement method
Hu Lili, Feng Guoying, Dong Zheliang
2015, 44(8): 2517-2522.
[Abstract](534) [PDF 1325KB](214)
A method of measuring excited modes in a fiber based on spatially and spectrally resolved measurement was adopted. According to the expression of the group delay of the fiber modes, the derivation processing of the group delay difference of transverse modes leading to the spectral interference was given as well as the corresponding simulation and analysis. The measurements for a standard communication single-mode fiber and a double-clad large-mode-area fiber were carried out. By using the single-mode fiber and optical spectrum analyzer to measure the spectral interference signal, the spectral interference signal by the Fourier transform was analyzed, and the distributions and power fractions of transverse modes were offered. The results show that the method of measuring the fiber modes based on spatially and spectrally resolved measurement can determine distributions and relative power levels of transverse modes in the fiber. When the high-order modes are weak compared with the fundamental mode, the interference between two different high-order modes can be ignored.
Influence of channel correlation on the signal scintillation with spatial diversity receiver
Shen Hong, Fan Chengyu
2015, 44(8): 2523-2527.
[Abstract](349) [PDF 1233KB](736)
In order to explore influence of channel correlation on the signal scintillation in free space communications system with spatial diversity receiver and provide references for design of the sub-aperture size and its distribution, the expression of channel correlation coefficient of spatial diversity receiver under weak fluctuation conditions was deduced in theory. The relationship between channel correlation coefficient and signal scintillation with spatial diversity receiver was obtained. Channel correlation coefficient under both horizontal uniform and whole layer download non-uniform turbulent propagation paths was numerically studied. For the plane wave, there is an obvious negative correlation property between sub-channels for aperture receiver under non-uniform turbulent propagation path. For the spherical wave, it is similar for both turbulent non-uniform path and uniform path for aperture receiver; the negative correlation properties are not obvious.
Blind equalization algorithm of wireless optical communication using subcarrier modulation based on subspace
Chen Dan, Ke Xizheng, Qiao Wei
2015, 44(8): 2528-2534.
[Abstract](403) [PDF 1760KB](144)
In this paper, subspace blind equalization algorithm of wireless optical communication using subcarrier modulation was studied based on Gamma-Gamma optical intensity scintillation distribution model. The constellations of the subcarrier multiple phase shift keying modulation signal through the atmospheric turbulence channel before and after the blind equalization was compared, and the bit-error-rate(BER) curves of the system under different scintillation distributions was given. When R=0.1 and SNB=20 dB,the BER was reduced from 4.710-1 to 1.5610-3. The BER performance was obviously improved. At the same time, measured data in two kinds of weather conditions(cloudy,rainy) which were described to atmospheric channel, was used in the experiment of subspace blind equalization. Clustering performance and phase identifiability of the constellation after equalization are obviously better than before equalization. The simulation results show that the subspace blind equalization algorithm has a good effects on equalization of subcarrier modulation signal under the atmospheric turbulence channel.