2013 Vol. 34, No. 6

OE System and Engineering
Design of double visual field flexibility change-over imaging system
WANG Xu-an, HUANG Jun-tao
2013, 34(6): 889-893.
Aiming at the visual field change-over of electro-optical system, a flexibility change-over method was presented to improve the accuracy and speed of the visual field change-over. The double visual field integrated coaxial and total imaging surface optical system was designed to meet the requirements of miniaturization and light-weight for the electro-optical imaging system of a certain electro-optical tracing device. Using the polarization principle of polarizer, the electro-optical systems of these two large and small visual field were divided into two optical channels of pitching polarization and yawing polarization. Using the liquid crystal rotator (two positions of 0,90) and the polarize principle of polarizer, time-sharing (flexibility change-over) gating of these two optical channels of pitching polarize and yawing polarize was carried out. The test result shows that the (flexibility) change-over time of these two optical channel is milliseconds only, which is 1% of the mechanical change-over. The double visual field flexibility change-over imaging system technical solution is feasible, and can meet the requirement of the certain electro-optical tracing system.
Design of multi-optical-axis and multi-spectral collimation system
JI Xiao-hui, YANG Lu, JIANG Xu
2013, 34(6): 894-897.
To calibrate the optical axis consistence of airborne multi-spectral and multi-axial optoelectronic tracking device fast and accurately, a calibration system for the consistence of optical axis based on Cassegrain optical system was designed. This system used halogen lights as the visible light source, blackbody as the infrared light source, and ZnS reticle was adopted to provide infinite object. The aperture of the system was 200 mm, and the focal length was 1 500 mm. The emergent beam parallelism of points on the axis was better than 10, satisfying the demand of 1 in the test of consistence of multi-optical axis and multi-spectrum system.
Design and research of equal-thickness slab Fresnel lens
YANG Guang-hui, WEI Ming, CHEN Bing-zhen, DAI Ming-chong, GUO Li-min, WANG Zhi-yong
2013, 34(6): 898-902.
The curved Fresnel lenses are usually found problematic in application, such as high process complexity, difficulty in surface accuracy control, high production cost and so on. To avoid these problems, based on studies of unequal-thickness slab Fresnel lens design, we propose a slab Fresnel lens design method that employs spherical center lens, inclined outer ring and equal-thickness surface. Specific design examples, as well as their computer optical simulation are given in this paper. Simulation result shows the optical efficiency of the Fresnel lens design achieves 90.7%. This kind of design provides a reference for engineering applications of the Fresnel lens applied in high concentrating photovoltaic modules.
Optical system of collimator for ultra-short pulsed Laser
XIE Zheng-mao, HE Jun-hua, QI Wen-bo, WEI Ming-zhi
2013, 34(6): 903-908.
In order to improve the collimation precision of ultra-short pulsed laser, an optical system of collimator based on auto-collimation theory was proposed. Beam spread collimation optical system providing a parallel precision of 3.2, which is illuminated by fiber coupled laser with a wavelength of 670 nm, was designed. As well as, an off-axis parabolic mirror of principal laser with the focal length of 350 mm, relative aperture of 1/5, and off-axial distance of 50 mm, was designed, and the imaging quality could reach the diffraction limit. Based on the collimating optical system and off-axial parabolic mirror, the 20 and 100 imaging systems working at wavelength of 670 nm and 800 nm synchronously were designed. An installation and alignment method based on pinhole collimation was proposed. The results of experiment illuminated by indicated light show that the image spot is even, and its resolution can reach to 4.1 m in the object space.
Multi-caliber-launching and large-caliber-receiving techniques for field atmospheric laser communication
MENG Li-xin, , LIU Kun-ming, ZHANG Li-zhong, BI Lei, SUN Jian
2013, 34(6): 909-913.
Aiming at the problem of atmospheric attenuation and intensity fluctuation of the field operations wireless laser communication, the effect of atmosphere on laser communications was analyzed, the suppressing mechanism of the atmosphere adverse effects using multi-caliber-launching and large-caliberreceiving was explored on laser communication. A multi-caliber-launching and large-caliber-receiving test device was built. The number of emission caliber was adjustable on emission end, and the Cassegrain structure was used in optical antenna on receiving end. The antenna caliber could be changed by adding different calibers apertures in front of optical antenna. When the number of emission caliber was increased to 4 beams, the value of light intensity fluctuation variance was about 1/2 of the single beam. And with the receiving aperture diameter difference of 1.5 times, there was a 1.6 times difference between scintillation variance. The multi-caliber-launching and large-caliber-receiving inhibitory effect of atmospheric turbulence was validated by experiments. According to the test results, some parameters of laser communication terminal of were optimized.
Accurate star centroid extraction for shipboard star sensor
TONG Shuai, LI Hui, WANG An-guo
2013, 34(6): 914-919.
Star centroid extraction is an important basis of star sensor. As for the complicated noise condition of offshore star image, a new star extraction method based on gravity method was proposed, which included four steps: block scan threshold segmentation, noise rejection based on star continuity, star extraction considering gray information and gravity method for centroid coordinate calculation. The algorithm was proved in experiments using 30 offshore star images that it could extract at least 10 stars centroids correctly with a success rate of 100% and an accuracy of 1/20 pixel while achieving real-time processing for video. Application requirements of shipboard star sensor could be satisfied.
Design of small star simulator system
ZHANG Jie, ZHANG Tao, KUANG She-qing
2013, 34(6): 920-927.
Based on the working principle of the small P13XM015-TFT-LCD star simulator and its designing, manufacturing, processing, debugging and detection technology of the whole system during the engineering application, the detection method for the two parameters of the small star simulator such as intersatellite spacing and magnitude was studied. The inter-satellite spacing was corrected by software then measured respectively and recombined to be corrected, while the adapted instrument magnitude method was used for the magnitude testing. The optical system collimating lens, preparation of simulator star database, coordinate transformation, position calculating, and system control software of the small star simulation system were designed by using modularity method. The assembly of the entire system was implemented in the laboratory, the controlling and testing platform was set up, and then the experimental results were obtained. The results show that, this system has high reliability with star database precision and position calculating error of no more than 2and angular resolution error of no more than 3.43.
Dynamic MTF measurement method of electro-optical systems
YU Xun, SONG Wu-han, WANG Ying, MA Lin
2013, 34(6): 928-932.
Under moving condition, the imaging process of optoelectronic system is a dynamic process in a certain period of the integration time. Therefore it needs to invoke the concept of dynamic modulation transfer function (MTF) to evaluate the impact of motion on the imaging quality. By designing a dynamic MTF testing system, the data processing and theoretical analysis for variation of the dynamic MTF were carried out under the moving conditions. Experimental results show that when it is the high frequency vibration, with the increase of the amplitude, the impact of MTF is stronger and the MTF value of the difference is 0.01~0.1 compared with static conditions; when low-frequency vibration, with the reinforcement of vibration frequency as well as the increase of amplitude or integration time, the MTF decreases obviously and the MTF value of the difference is 0.01~0.5 compared with static conditions.
Surface defects of PVD modified RB-SiC
KANG Jian, XUAN Bin, XIE Jing-jiang
2013, 34(6): 933-937.
In order to obtain the high surface quality of physical vapor deposition (PVD) modified RB-SiC mirror and solve the problems of the surface defects in the practical processing, we conducted studies on the forming mechanism and the processing method of defects. According to Preston hypothesis, it was deduced that higher impact on the large rimes in PVD layer could be the main reason which may cause surface defects. The experiment proved that the defects would appear if the polishing speed or the polishing presure was too high. In order to reduce and avoid surface defects effectively, it was reasonable to control the relative polishing speed and polishing pressure, in the meanwhile, the polishing efficiency could be maintained. According to the analysis above, the surface defects could be renovated after 0.7 m~1 m of coating material was removed with the proper polishing speed and pressure, while new defects did not appeare any more.
Interferometer based on photoelastic modulator
ZHANG Rui, WANG Zhi-bin, LI Jin-hua, YANG Qiang, HUANG Yan-fei, WANG Yao-li, ZHANG Peng-fei
2013, 34(6): 938-942.
Single photoelastic modulation (PEM) interferometer has the limitation of thermal and mechanical in the material, so the modulated optical path difference is small, however, series PEMs are difficult to control, and the multiple reflections of various PEM interface make the energy of light lost. Therefore, a method of effectively improving optical path difference by multiple reflections was put forward, based on one single PEM posted on the total reflection film. By deducing and analyzing the influence of the different reflective situation on the optical path difference, the formula of the optical path difference was got after multiple reflections of incidence in arbitrary angle and position. The method was proved by COMSOL, MATLAB, ZEMAX simulations and experiments. The adopted photoelastic crystal was ZeSe and the piezoelectric crystal was quartz. Result shows that the relative error of experiment and theory is 0.21%, which provides the theoretical basis for the engineering application of this method.
Optical design of dual field-of-view imaging spectrometer with filters
FEI Xin-lin, FU Yue-gang, LIU Zhi-ying, WANG Yuan-peng
2013, 34(6): 943-946.
In order to meet the practical requirement of airborne searching and tracking systems, a dual field-of-view imaging spectrometer with filters was designed based on the theory of zoom system and imaging spectrometer.The CCD of 1/3 inches was used, and the size of the pixel was 6.0 m6.0 m .The initial structure was obtained by using the Gaussian method, the system was optimized by using Zemax software. Dual waveband (0.45 m~0.7 m/0.6 m~0.95 m) clear imaging was achieved, axial moving group could complete double field-of-view switch(139.75/32.25). In this process, F number was 5.6 and constant. The design results show that the distortion of the wide-FOV is less than 3.5%, the distortion of the narrow-FOV is less than 0.2%, The peak values of MTF are more than 0.5 at Nyquist 50 lp/mm and the minimum back intercept range of the system is greater than 35 mm to install filters, which meets the assembly requirements.
Two-mirror system design with afocal corrector placed on secondary mirror
TENG Guo-qi, JIAO Ming-yin, HU Bo, CHANG Wei-jun, WANG Ling
2013, 34(6): 947-950.
The design method of a two-sphere system with an afocal corrector which was on the secondary mirror was described. The basic theory for solving the initial structure by using PW method was analyzed. By changing the obstruction ratio K and the length from primary mirror to focus , the ray tracing was realized, the optimized combination of K and was obtained. An design example was given: the working band of the system was 450 nm~700 nm, focal length f was 1 600 mm, relative aperture A was 1/8, visual field angle was 0.5, obstruction ratio K was 0.35, and the length from primary mirror to focus was 0.1. After the optimization of the system, the coefficient of spherical aberration SⅠ-was -0.001 207, the coefficient of comatic aberration SⅡ was 0.000 192, and the wave-front aberration W was 0.043 27.
OE Information Acquisition and
MS-KF fusion algorithm for drogue tracking
WANG Xu-feng, DONG Xin-min, KONG Xing-wei, ZHI Jian-hui, WANG Long
2013, 34(6): 951-956.
A mean shift-Kalman filter (MS-KF) fusion algorithm for drogue tracking in unmanned aerial vehicle (UAV) autonomous aerial refueling (AAR) was proposed. The drogue tracking theory based on mean shift (MS) algorithm, including drogue aim model, similarity measurement and drogue positioning, were analyzed. By introducing Kalman filter (KF), the drogue moving information was predicted and merged in MS algorithm in order to ensure the stability and robustness of the drogue tracking algorithm. The flow block diagram of drogue tracking based on MS-KF fusion algorithm was provided and the semiphysical experimental system of drogue tracking was constructed. The semi-physical verification experiment and numerical simulation analysis of MS-KF algorithm for drogue tracking were respectively conducted. Experimental results demonstrate that the MS-KF fusion algorithm can position and track drogue precisely and the tracking errors of the UAV axes keep within the range of 0.3m, which ensures the success of the UAV-AAR.
Electronic image stabilization based on improved gray projection
GU Xue-hai, WANG Li-ping, GU Guo-hua
2013, 34(6): 957-963.
Gray projection method for electronic image stabilization has poor image stabilization effect and it may cause the error stability when there is a moving target in the image sequence. In order to solve the problem, we proposed an improved gray projection algorithm which referred to the position estimation method for partial moving target and the pixel alternative method, based on the analysis of the basic theory for gray projection. We estimated the position of the partial moving target using a change of gray value, and removed the partial moving target with the method of pixel alternative to stabilize image. Through analysis and verification, the conclusion is that this method can well process the image which has problems and improve the image stabilization effect. Using the improved method, the peak signal-to-noise ratio (PSNR) is increased by 1.35.
Camouflage assessment based on hyperspectral characteristics
HUA Wen-shen, YANG Jia, LIU Xun, MA Zuo-hong
2013, 34(6): 964-967.
Camouflage assessment is an essential part in camouflage design and identification. In order to make an effective camouflage evaluation under the hyperspectral detection, we presented a new method based on hyperspectral characteristics considering the characteristics of high spectral resolution of hyperspectral images. Firstly, the spectral information was extracted and analyzed in spectral dimension. Then, the multi-wavelet decomposition was used in spatial dimension of the first principal components to extract texture information such as the ratio of high frequency component and low frequency component, ratio of horizontal component and vertical component, contrast, correlation, energy and homogeneity of low frequency image. Finally, Euclidean distance was calculated to reflect the similarity of spectrum and texture. Experimental data demonstrates the objectivity of the approach. The comprehensive distance between camouflage raincoat and lawn background is 1.3225 that proves they fuse best.
Comparison experiment of color correction for color vision device
ZHU Zhen-min, ZHONG Lu-sheng, TU Hai-yan, JIN Xiao-long
2013, 34(6): 968-973.
Automatic vision measurement by color vision device is the development trend of color measurement for industrial application. The average color reproduction error of illumination and the spectral response functions of camera have a strong impact on the measurement accuracy. Therefore, the correction images were obtained by the same camera under the artificial D65 illuminator and the LED array illuminator, respectively, the color correction was performed by polynomial regression method in standard red green blue (sRGB) and CIEL*a*b* device-independent color space simultaneously. Results showed that before correction, the color differences of images were 27.68E and 16.09E, respectively, meaning illuminated by artificial D65 illumination was less than illuminated by LED array illumination; After correction, the color of images obtained by different illuminators was close to each other, the average color differences were 2.56E and 2.39E, respectively. Using sRGB as the device-independent color space was better than CIEL*a*b* color space due to the high accuracy, the simple correction process and the convenience of image display. Finally an actual picture captured by color measurement device was corrected in sRGB color space. The results showed the importance of correction for color vision device.
Image compression used improved error back-propagation neural network
2013, 34(6): 974-979.
To overcome the dramatically increasing data amount of space remote sensing image, an improved back-propagation(BP) neural network was put forward to compress it. The algorithm used the Levenberg-Marquart algorithm to improve the convergence speed of neural network and used algorithm to improve the generalization ability of neural network. We compared and analyzed the compression result and error performance function of the improved algorithm and the standard BP algorithm to the same image. The experimental results show that, when the image compression ratio is 1/2, the mean square error (MSE) of standard BP algorithm is 343.3750; for improved BP algorithm, the MSE is 69.5796 when the image compression ratio is 1/16, the MSE is 20.9561 when the image compression ratio is 1/8, and the MSE is 5.5123 when the ratio is 1/4. Moreover, the peak signal-to-noise ratio (PSNR) of the improved algorithm is always in the range from 30 dB to 40 dB. The improved algorithm has been applied in practical engineering, which meets the need of practical work.
Color image encryption technology based on asymmetric cryptosystem
WANG Hong-juan, ZHANG Ying-ying, HUANG Yi-ding, MA Mao-fen, QIN Yi
2013, 34(6): 980-984.
In order to encrypt color image, a method based on Fourier transform and asymmetric cryptosystem is proposed. Firstly, a color image is separated into three primary components: red, green, and blue. Then Fourier spectra of the three gray images are intercepted respectively and combined into a target image, and the target image contains most of the original color image information. The amplitude and phase of this target image are encrypted using asymmetric cryptosystem, which means the original color image is encrypted. In this paper, the theoretical analysis and computer simulation are proposed, and the experiment results verify the feasibility of this method.
Advanced EM algorithm based on Gaussian mixture model
SONG Lei, ZHENG Bao-zhong, ZHANG Ying, YAN Li WEI Hong, LIU Jian-peng, LI Tao, YANG Heng
2013, 34(6): 985-989.
In order to solve the disadvantages of traditional expectation maximization (EM) algorithm which lacks parameters optimization and needs human operation when estimating parameters, an improved EM algorithm based on Gaussian mixture model was proposed. The unsupervised theory was used to calculate optimal Gaussian mixture model parameters. The subjective and objective indices of experiments show that the algorithm can not only estimate parameters quickly but also figure out the optimal parameters, making the detail more obvious and the contrast more moderate in image enhancement application.
Optical Metrology and Measurement
Laser interference differential measurement of micro impulse based on torsion balance
YE Ji-fei, HONG Yan-ji
2013, 34(6): 990-994.
Based on the impulse measuring principle of torsion balance, a kind of laser interference differential method of micro impulse was advanced. The system setting and measurement procedure were introduced. The torsion balance structure design parameters were given. The calibration and verification were put forward. The system resolution, measurement range and precision were calculated. In the typical measurement condition, the micro impulse generated by the laser ablation was measured with the method, the typical result was given and analyzed. The results show that the system resolution of the method is competent for the 10-7 Ns magnitude, the measurement range covers five magnitudes, the maximum magnitude is 10-2 Ns with precision better than 95%.
Restoration of degraded edge in size measurement based on CCD image
LIU Bin, WANG Li-ming, ZHAO Xia
2013, 34(6): 995-999.
For image edge degradation problems caused by straight edge diffraction, an edge degradation model was established. Starting from Fresnel diffraction theory, reasons for image edge degradation were discussed based on mathematical description of image edge degradation of signal and system theory. By analyzing the characteristic of intensity distribution curve of straight edge diffraction in case of different wavelengths of light source and distances from image and object, a simple function was used to represent distribution of straight edge diffraction, and the transfer function of the degradation system was obtained. Then the transfer function of the degradation system was used to realize the restoration of the degraded edge. Experimental results indicate that the presented method has better effects on restoration of the degraded edge caused by straight edge diffraction. The measurement error based on corrected data is 0.02 mm, which reduces 0.04 mm comparing to the measurement error based on original data.
Measuring method of temperature coefficient of infrared optical material transmittance
XU Rong-guo, WANG Lei, YIN Wan-hong, YANG Zhao-jin
2013, 34(6): 1000-1004.
A new transmittance measurement and assessment method of the infrared optical material at diffident temperatures was proposed. A collimation reflect mirror was used to make the infrared light source into the parallel light, and then a chopper was used to make the continuous light into the pulse light, besides, a special wavelength was obtained by filter. A special data acquisition system that including a preamplifier circuit, a lock-in amplifier, a computer and a control software could calculate the value of infrared transmittance and give the temperature coefficient of the optical material by means of double light beam contrast measurement. The method resolved problems of infrared transmittance measurement of optical material in actual operational environment, like high temperature. Test result shows the transmittance of sapphire material is higher than 10% at the wavelength of 519 5 nm, and the repeatability is better that 0.2% from room temperature up to 700℃. The method has great economic and social utility.
Optical and digital holography for spray measurement
XU Qing, CAO Na, CAO Liang, LEI Lan, HAN Chang-cai
2013, 34(6): 1005-1009.
Aiming at the problems that the development of holographic plate is cumbersome and the acquisition of the reconstruction image is time-consuming during the spray measurement with optical holography, a method of simultaneously using optical holography and digital holography was proposed, and a system consisting of in-line optical holography, in-line digital holography and digital delay signal generator was established. Spray field produced by doublehole direct injection nozzle was measured by the system. The reconstructed images of optical holography and digital holography were obtained during a single measurement, and they were in good agreement with each other. The range of the field of view was 27.87 mm4.77 mm and 27.59 mm6.67 mm, corresponding to optical and digital image reconstruction, and the acquisition time of digital holographic image reconstruction was only 8 s. The results show that a real-time assessment for the experiment effect can be made by the digital holographic image reconstruction, during the joint measurement of optical holography and digital holography, so the efficiency of holographic measurement experiment for spray field is improved.
Detection method of random error for dynamic measurement accuracy of photoelectric theodolite
ZHAO Huai-xue, ZHAO Jian-ke, TIAN Liu-de, DUAN Jiong
2013, 34(6): 1010-1013.
To achieve measuring stochastic error for the dynamic measurement accuracy of the photoelectric theodolite and to improve detection ability of the photoelectric theodolite, a detection method of stochastic error was developed. Based on Burse-Wolf model, the theoretical equation for the angle of azimuth and elevation was developed. According to the theoretical equation and based on the azimuth angle, the elevation angle and the sampling time of the photoelectric theodolite, the theoretical truth-values of the azimuth angle and the elevation angle were obtained, and the random error was obtained from comparing the theoretical value and the measured value. A novel method for measuring stochastic error for the dynamic measurement accuracy of the photoelectric theodolite was presented.
Circular hole size measurement system based on computer vision
WU De-gang, ZHAO Li-ping
2013, 34(6): 1014-1018.
For detecting the common circle objects, a circular hole size detecting system based on computer vision was developed. Using mixed noise filtering,fuzzy and genetic algorithm, the edge of circular hole image was extracted from the collected parts image. The radius and area of circular hole were measured accurately by interpolation method for roundness measurement. The testing results show that the average error of the system is 0,010 5 mm. It is far less than 0,0273 mm, which is the average error of manual measurement system. It can meet the precise requirement in industrial applications.
Infrared Technology
Athermal design of two-color infrared common aperture optical system
GUO Sheng-nan, FU Yue-gang, LIU Zhi-ying, MA Chen-hao
2013, 34(6): 1019-1024.
Aiming at the needs of infrared (IR) searching and tracking system for target detection, a two-color infrared common aperture system was designed in order to improve the detection ability of optical system under complex environment. The working waveband of the system covered the medium-wave(3 m~5 m) and long-wave(8 m~12 m), the dual-band clear imaging was achieved by using dispersive Ritchey-Chrtien (RC) system, the overall focal length of the system was 400 mm, the relative aperture D/f was 1/2, and the full field of view was 2. In order to suppress the medium-wave thermal radiation stray light, the mid-wave infrared (MWIR) system achieved the secondary imaging, through rational calculation of IR material and focal power, the optical passive athermal design was achieved. The results indicate that the image quality is excellent under the working temperature of -40℃~+60℃, which can meet the using requirement of infrared searching and tracking system.
Small target detecting method using dual-craft IRST image matching and fusion
XU Qiang, WANG Hai-yan, YANG Hai-yan, CHEN Xin, WANG Fang
2013, 34(6): 1025-1029.
Aiming at the problem that the small target was hard to be detected from infrared image in single craft-s infrared search and track (IRST) system under disorder background and great yawp situation, due to the limit of detecting distance and precision, the dual-craft coordinated detecting of the same target area at the same time was used. Then the process of images matching and fusion was conducted, in which a multi-rule algorithm that the high frequency based on area and the low based on pixel was adopted, and a target detecting method based on wavelet transform and edge information token was proposed after the fusion. The emulation experiment shows that the multi-rule fusion algorithm can improve the evaluation index of images quality by from 30% to 50%, and the method can eliminate false targets from 7 to 3,filter disturbing waves, reduce the false alarm rate and detect small targets efficiently and accurately.
Laser Technology
Quantitative calculation of pump-light's influence degree on mode of oscillating laser
WANG Shi-yu, XU Ming-shun, LIU Guo-rong, LIN Lin, WEI Yong-hui
2013, 34(6): 1030-1035.
In laser rod, the unevenly distributed pump-light caused the gain function vary over the medium, which could bring changes on the mode of the oscillated laser. A method was developed to estimate the influence degree of the non-uniform pumping light on the laser mode, by which the deviation of the oscillating field from its origin form could be given in terms of percentage. Based on it, a quasi-continuous three directional side pumped laser was discussed, in order to find the feature of the affection that the varying pumping light acted on the oscillating laser. Result shows that the changes of the oscillating mode brought by the pumping light have monotonic relations with the pumping power and the cavity loss, and the influence of pumping light on oscillating field only depends on its variation over vertical section, and is free from the distribution along the propagation direction of the oscillating laser. The magnitude order of the effect is obtained through numerical calculation, which is less than 4% when the pumping power is 2 000 W and is larger than 20% when the pumping power is 6 000 W.
Influence of curvature variation on loss and performance of ring laser gyro
WANG Peng-guo, YE Ping, HU Qiang
2013, 34(6): 1036-1040.
In order to study the influence of different curvatures on the performance parameters of ring laser gyro (RLG), the diffractive loss calculation model was established in theory based on the cavity theory. The waist variation of RLG resulted from the curvature variation assembly was calculated by simulation, which could further cause diffraction loss variation. And starting from the effect of aperture diffractive loss on the backscattering of RLG,the influence of waist on the performance of RLG was analyzed. The calculated results indicates that the variation of diffractive loss is 3% when the variation of the curvature radius is less than 0.3 m, which would cause the bias varying 0.013 Hz; the variation of diffractive loss is 15% when the variation of the curvature radius is about 0.6 m, which would cause the bias varying 0.021 Hz; thus, the variation of diffractive exceeds to 30% when the variation of the curvature radius is more than 1.5 m, which would cause the resonator detuning, that is no laser comes into being. Both loss and bias were measured when the curvature was changed. The test results accords with the theory, the variation of curvature has obviously effect on diffractive loss and its performance.
Analysis system of Mie scattering parameter based on MATLAB and LabVIEW
ZHANG Nian-jun, GUO Feng, LI Heng, ZHONG Ying, YANG Kai
2013, 34(6): 1041-1046.
In view of process of measuring 0.1 m~10 m particles with laser scattering method, the parameters-analysis, calculation and optimization of its selection on Mie scattering theory are complicated and cumbersome. Through the comparison on convergence speed, refractive index, scale parameter measurement range and superposition times, we adopted an improved algorithm of Mie scattering parameter based on MATLAB. By combining with MATLAB-s strong computing power and LabVIEW-s graphical interface we did the mixed programming of LabVIEW and MATLAB, and designed a parametric analysis system on theory of Mie scattering which mainly calculated and analyzed the scattering coefficient, the relationship curve between scattering coefficient and particles diameter, the distribution curve of scattering intensity, the effect of incident light-s wavelength, particle-s diameter and polarization angle of incident light on the scattering intensity. The comparison between experimental results and conclusions shows that the system is feasible and the reckoning of scattering coefficient, extinction coefficient and the scattering intensity can be accurate to 17 decimal places, thus it achieves the purpose of reducing a large number of computation and programming work.
Implementation of pulse peak holding circuit based on laser spot tracker
MU Rang-xiu, NING Zi-li, BI Bo-rui, HOU Feng-qian, XUE Chang-jia
2013, 34(6): 1047-1050.
A kind of pulse peak holding circuit was designed to fulfill the technical demands of conventional A/D sampling circuit to capture peak voltage in the reception signal processing system of laser spot trackers. Firstly, several technical specifications of the holding circuit were analyzed theoretically and the MAX436, a high-speed and wideband trans-conductance amplifier, was effectively chosen to lay out the circuit. Following, the simulation analysis and experimental research were done to get experimental results that could meet the technical demands. For the laser pulse signal of 50ns pulse-width, the response speed of the peak holding circuit2 ns, the relative error1.1% and the droop speed rate6.0 mV/s, when the amplitude of input signal100 mV.
Fiber Sensing and Optical Communication
Polarization dependent loss in direct detection optical OFDM systems
HAO Yao-hong, LENG Dan
2013, 34(6): 1051-1056.
Polarization dependent loss (PDL) and polarization mode dispersion (PMD) in direct detection optical orthogonal frequency division multiplexing (DDO-OFDM) system influence performance seriously in high speed transmission. The mathematical model and mechanism of transmission were analyzed in DDO-OFDM systems. Analysis and simulation results show that, PDL and PMD may bring amplitude and phase noise which could be eliminated by signal equalization. Meanwhile, PMD may mitigate the effect of PDL because of the rotation of the state of polarization(SOP). The system Q value is improved by about 0.8 dB for 480 km distance and speed of 10 Gbit/s transmission through standard-single-mode fiber (SSMF) with the differential group delay (DGD) of 50 ps.
Validation of high-Q optical microsphere resonator angular velocity sensor
ZHANG Jian-hui, XU Peng-fei, LI Xiao-feng, XUE Chen-yang, LIU Jun, YAN Shu-bin
2013, 34(6): 1057-1061.
An angular velocity sensing experimental measurement system, with high-Q optical microsphere cavity as the core sensitive component, was set up based on the theory of angular velocity sensor. During the experiment, the resonance curve of optical microsphere cavity and the corresponding demodulation curve were obtained by the modulation and demodulation; the lock-tracking of resonance point by the proportional-integral-derivative (PID) feedback control circuit was achieved, and the locked accuracy of resonance point was about 10 kHz. The experiment for testing two different rotating angular velocities, low and high, was carried out, then the data was analyzed to obtain the result of the trend of the output signal amplitude corresponding to the change of the rotational angular velocity provided by the test table. The sensing effect of high-Q optical microsphere cavity angular velocity was proved preliminarily, which could provide the foundation for the further research of high-Q optical micro-resonator angular rate sensors.
Contour detection based on optical-fiber acousto-optic modulation
GAO Chuan-mei, WANG Hui-lin
2013, 34(6): 1062-`065.
In order to meet the requirements of component surface micro-topography measurement system for remote transmission and real-time online non-contact measurement, as well as high accuracy, high resolution and high signal-to-noise ratio measurement, we presented an optical-fiber heterodyne method of contour detection based on acousto-optic modulation. We established the mathematical model through the principle analysis, drew the suface roughness measurment block diagram and measured the suface roughness of the testing component with achieving the resolution of 1 nm. Moreover, we discussed the source of uncertainty and control method, the measurement accuracy was 1. Results show that the noise, resolution and measurement can be improved by the fiber-optic hererodyne contour detecting technique based on acoustooptic modulation.