2013 Vol. 34, No. 1

OE System and Engineering
Testing device for modulation transfer function of push-broomelectro-optical imaging system
HE Xu, WU Guo-dong
2013, 34(1): 1-8.
The optical remote sensing system obtains a high resolution imaging of ground targets by the imaging model of linear array CCD push-broom. And the modulation transfer function (MTF) is a key parameter to evaluate the imaging quality of push-broom system. Using the black and white stripe target as a square wave signal of Nyquist frequency to test the static MTF can evaluate the imaging quality of system quantitatively. However, an electrooptical imaging system with linear array CCD push-broom model has to test its dynamic MTF under the image motion compensation and drift angle control condition, and then the imaging quality of system in the real working condition can be evaluated. Based on the theory of dynamic and static MTF testing methods, we studied the constitution and the working principle of testing device, and gave a detail designing for collimator, static and dynamic target generator. The wavefront error of collimator was better than 25 nm (RMS). The focus length adjusting accuracy was better than 3 m. The output accuracy of image motion compensation was better than 5/1 000. And the illumination uniformity of system was better than 95%, which could realize a theoretic non-coherent illumination. The simulated designing above could satisfy the dynamic and static MTF testing requirement for the new optical remote sensing imaging system in laboratory.
Light-gathering ability of optic micro-lens molded on needing position
WU Jian, LIU Wen-cao, YU Kuan-xin, CHEN Tao, LI Ying-hui, WANG Chun-yan
2013, 34(1): 9-14.
In order to solve the difficulty for manufacture of micro-lens in micro-detector of fluorescent spectrum, a new manufacture technique of micro-lens, molded on needing position, was proposed. Light gathering ability of the optic micro-lens was researched. Using principles of traditional geometric optics, ray tracking equations of stimulating micro-lens and detecting micro-lens were derived. Distributed probabilities of illumination points for the two micro-lenses were calculated by using these equations. Some corresponding distributed curves were given. Influence of the micro-lens-s shape on the light gathering ability was discussed. Results indicate that the contact angle between optic glue and glass base can be decreased and the shape parameter of the microlens can be increased by adulteration in the optic glue and milling the glass. It can both strengthen adhesiveness between the glue and the glass, and increase light gathering ability of the micro-lens. A micro-detector for fluorescent spectrum with micro-lens molded on needing position was manufactured and the biological fluorescent reagent was measured. Experiment results indicate that the intensity of the biologic fluorescent spectrum can be increased more than 4 times by using micro-lens molded on needing position, the light gathering ability of the micro-lens can be increased 1.2 times though adulteration in the glue and milling the glass.
Performance comparison and analysis of coarse and fine combinedstabilization control system based on mirror compensation
XU Fei-fei, LIU Sha, YIN Ming-dong, JI Ming
2013, 34(1): 15-20.
The principle of coarse and fine combined stabilization control system for optoelectronic stabilization platform was introduced. Two assumptions of the systematic model were proposed according to the different structures of the fast steering mirror (FSM). Based on the two assumptions, the frequency character and stability of system were deeply analyzed. Results show that the performance of the combined stabilization control system is mostly depended on the bandwidth ratio of the major to the sub-system and the choice of the combined controller K.
Wide spectral SWIR star sensor optical system
ZHAO Kun, CHE Chi-cheng
2013, 34(1): 21-25.
Observing star in shortwave infrared (SWIR) spectrum has been considered as one of the important development directions of star sensor. According to the characteristic of wide waveband used in SWIR star sensor and the two feasible methods for correcting secondary spectrum in theory, an SWIR star sensor optical system with 900 nm~1 700 nm band, F number of 1.5 and the equivalent focal length (EFL) of 150 mm was designed based on the method of selecting the glass combination of the same or nearly relative dispersion coefficient and obviously different dispersion coefficient. Result shows that the secondary spectrum is corrected in broad band, the MTF in full field of view is more than 0.65 at 32 lp/mm.The system has excellent performance that can satisfy the requirement of observing star in near infrared band.
Optical design of visual simulation lens for dynamic target simulator
WEI Zhong-lun, LIU Wei-qi, LIU Hua
2013, 34(1): 26-31.
A kind of visual simulation lens for dynamic optical target simulator based on liquid crystal light valve was studied and designed. The dynamic optical target simulator was composed of LCD display system, visual simulation lens, external projector, computer, cable, and adjustable mechanism. According to the instruction from the testing equipment, the simulated image of earth was generated and the liquid crystal light valve was controlled to display the simulated image of earth by computer. The liquid crystal light valve was situated on the focal plane of the visual simulation lens. Light coming from the dynamic optical target simulator was parallel light, and infinite analogue observation effect could be generated in a finite distance. The optical sensor gathered the light coming from the visual simulation lens and finished imaging simulation. Inversed telephoto structure of secondary imagery method was adopted by visual simulation lens, and in order to match the emergent light of liquid crystal light valve, telecentric beam path structure was also adopted. The focal length of the visual simulation lens was -22.447 mm, the field angle was 45,and the effective field of view was 301.5301.5. The barrel distortion of the visual simulation lens was smaller than 1%, the modulation transfer function (MTF) was greater than 0.45 at Nyquist frequency, and the length of the visual simulation lens was 325 mm. Illumination uniformity of optical sensors was better than 95.4% under the coordination between the visual simulation lens and the optical sensor. Finally the test results of the visual simulation lens were listed.
Optical receiving antenna based onmovable transmitting antenna
LIU Feng, WANG Ji, DING Jie, XU Yuan-fei
2013, 34(1): 32-37.
A refractive optical receiving antenna that was used in the multi-transmitter multi-receiver free space laser communication system was designed. The focal length of the antenna was 120.02 mm and relative aperture was 1∶1.13. The antenna-s working wavelength was 850 nm and wavelength range was 820 nm ~880 nm. The MTF of 0 field of view was 0.5 at the spatial frequency 50 lp/mm. In the transmitting antenna movable range of 48 mm, the receiving antenna could receive the optical signal of 3 mrad divergence by using the avalanche photo-diode(APD) with 0.5 mm diameter of photosensitive surface. This refractive optical receiving antenna was composed of 4 spherical lenses, was simple in configuration, and could receive the optical signal from movable transmitting antenna.
Optical design of high-magnification zoom stereo microscope objective
XU Li-feng, ZHANG Xin, QU He-meng, HUANG Xin, WANG Chao
2013, 34(1): 38-44.
In order to achieve high-magnification in continuous zoom stereo microscope objective system and avoid using aspherical optics and diffractive elements, new methods of zoom compensation were adopted in zoom lens designing with double linkage moving lens groups. By choosing 6 zoom positions for designing and calculation, the zoom of 0.8~16(20∶1) stereo microscope objective system was achieved. The working distance of the system reached 91 mm, and the back focal length reached 200 mm. After analyzing modulation transfer function (MTF) and aberration of the optical system, the results show that this zoom stereo microscope objective system realizes high magnification and high imaging quality.
LED coupled device for fiber-optic illumination
FU Qian, SU Cheng-yue, ZHOU Zhen, HE Rong-li
2013, 34(1): 45-50.
Coupled device with LED light source for fiber-optic illumination is often composed of lens group. Though the convergence spot of this system is small, the light loss of lens group is big. Due to the characteristics of LED light source and the big aperture of polymer optical fiber, an side installation for LED lamp and an optimization method that reflector was cutted and shifted were put forward,and a kind of coupled device with LED light source based on elliptical reflector was designed. Using the approximation algorithm that had been proposed by John O-Farrell, the elliptical reflector-s structure parameters for different eccentricities were calculated. Through comparing the coupling efficiency by combining with the simulation of fiber-s optical parameters, a group of structural parameters of efficient coupled device that the eccentricity matched the fiber diameter were obtained. Using this method, a coupled device with LED light source was designed which had a fiber diameter of 10 mm and numerical aperture of 0.5.The ideal coupling efficiency was up to 93.35%.
Error reduction of optoelectronic tracking platform for switching fromcompound control to feedback control
LIU Xiao-qiang, LU Feng, LIANG Xiao-dong, XING Jun-zhi, SHOU Shao-jun
2013, 34(1): 51-55.
Control theory, simulation and experiment of EO system show that the tracking errors increase suddenly when the optoelectronic tracking platform switches the control mode from compound control to feedback control. To solve the problem, a constant compensation method was put forward. The method compensated the errors caused by the control mode switching and made the steady-state error state not increase after compensation, it decreased the tracking errors evidently. The simulation and experiment data prove the method is feasible.
Screening of LED for spectrum-tunable light source
LIU Hong-xing, REN Jian-wei, LI Xian-sheng, SUN Jing-xu, YE Zhao, ZHAO Wen-cai
2013, 34(1): 56-61.
In order to meet the requirements for lifetime and spectrum consistency of LED used in LED-based spectrum-tunable light source, 29 kinds of LEDs were seasoned for 200 hours separately under the accelerated current condition, and a spectral consistency screening algorithm was proposed. Results of ageing test indicate that the values of radiant flux attenuation of 3 kinds of LEDs, whose peak wavelengths are 385 nm, 400 nm and 420-1 nm, are 24.8%, 10.7% and 25.6%,respectively, so they are not suitable for LED-based spectrum-tunable light source. The values of radiant flux attenuation of the remaining 26 kinds of LEDs are all below 3.5%, and they are all suitable for LED-based spectrum-tunable light source. The spectral consistency screening algorithm is based on the LED-s spectroscopic data, and the relative spectral deviation among the same kinds of LEDs can be calculated. The relative spectral deviations of 26 kinds of LEDs are all below 4.5%, the spectral consistency of the screened LED can be ensured.
OE Information Acquisition and Processing
Automatic de-smearing algorithm for target in space observation image
ZHANG Jian, REN Jian-cun, ZHANG Chun-hua
2013, 34(1): 62-67.
In order to realize automatic correction for smear effect of high light target in space observation image, an automatic de-smear system was established, and its applied algorithms such as Gaussian noise distribution parameters estimation of image background, target smear detection and image gray-scale value correction were investigated. First, the Gaussian noise-s distribution parameter of star observation image was estimated with histogram least square curve fitting. Subsequently, utilizing the smear features in observation image, a smear detection algorithm based on statistical information was proposed. Then, after the smear position was determined, the contaminated pixel-s gray-scale value was corrected. Finally, a set of de-smearing system in star observation image was with Visual Studio 2005. Experimental results indicate that with the star observation image of 16 bit and 1 0241 024 pixel, the processing time of single frame image is about 300 ms. The smear effect is well corrected, and the useful information of stars and target is not destroyed. The processed image by our algorithm can satisfy the demands of stability, reliability and precision for dim target detection in space observation image.
Method of infrared target segmentation based on visual cognition
ZHANG Peng-hui, CUI Dong-xu, ZHANG Jun-ju, MIN Chao-bo, LI Ying-jie, SUN Bin
2013, 34(1): 68-73.
Based on the study of target segmentation in infrared image, a method of infrared target segmentation based on visual cognition was proposed, in order to solve some problems of over-segmentation or lack of segmentation, and insensitivity to the low gray target in gray-scale segmentation algorithm. Firstly, the gray information of infrared image was converted to image variance information; secondly, Chebyshev inequality and some other basic mathematical theories were used to calculate the variance threshold between the target and background, then complete the pre-segmentation of the target information; finally, the morphological filling operator was used to acquire the binary mask image of the target information in order to extract target in the source image successfully. The subjective and objective indices of experiments show that the algorithm of infrared target segmentation based on visual cognition can detect infrared targets in different gray levels effectively,and the misclassification rate of infrared target is very low.
Back analysis of aerosol optical thickness on Bohai Gulf based on MISR data
2013, 34(1): 74-78.
Based on the remote sensing data from multi-angle imaging spectroradiometer (MISR),the aerosol optical thickness was calculated. The traditional darkpixel atmospheric-correction algorithms considered that the aerosol optical thickness had homogeneous distribution above the study region. Taking into account the unreasonable traditional approach, Bohai Gulf was divided into 7 sub-regions. Using the traditional dark-pixel algorithm, the aerosol optical thickness of each sub-region was estimated. Then, space interpolation approach was adopted to calculate the aerosol optical thickness of the whole Bohai Gulf. The results show that, the aerosol optical thickness is lower on offshore area and higher on coastal zone. Comparing with the traditional darkpixel algorithm, the nonuniform distribution of aerosol optical thickness in space is fully considered by the sub-region dark algorithm, which is beneficial to improve the accuracy of atmospheric correction.
Filtering method for interferogram of spatial heterodyne spectrometer
WANG Xin-qiang, XIONG Wei, YE Song, ZHANG Li-juan
2013, 34(1): 79-84.
A denoising method for interferogram was proposed based on the improved spin filtering by analyzing the production and characteristics of the interferogram of spatial heterodyne spectrometer. Filtering was carried out on tangent fringe-pattern to reduce the influences of random and dark spot noises without changing the details of fringe-pattern. In addition, the background noise of average spectrum was effectively decreased, the ratio of characteristic spectrum to background noise was increased. Results show that by using the spin filter method, the SNR of the average spectrum of interferogram is improved by 47% without noise and 240% with noise, respectively, and the characteristic spectra with small peak values can be extracted from the background noise to improve the recognition rate of spatial heterodyne spectroscopy as far as weak characteristic spectrum is concerned.
Image SVD denoising based on PSNR and wavelet directional feature
WANG Min, ZHOU Lei, ZHOU Shu-dao, YE Song
2013, 34(1): 85-89.
An optimized image singular value decomposition (SVD) denoising algorithm based on wavelet transform directional information and peak signal to noise ratio (PSNR) was proposed. As most of the energy noises were concentrated in low-frequency sub-image after wavelet transform, the simple Wiener filtering was made; on the other hand, the image noises were mainly concentrated in the high-frequency sub-image with three different directions and the coefficient was smaller, so the larger singular values of SVD and their corresponding eigenvectors were used to reconstruct denoising image; however, because of the inherent directional feature of the SVD, the denoising result of image reconstructed from high-frequency diagonal sub-image was not satisfied, so the diagonal sub-image was rotated to the level (vertical) direction, then the SVD filtering was done; finally, the anti-wavelet transform was used to reconstruct the denoising image based on the low-frequency and high-frequency sub-images, and the required number of singular values was determined by PSNR of the image. Experimental results show that this method has effective denoising effect, while retaining the high-frequency original details.
Restoration of motion-blurred image by generalizedinverse method based on SVD
LU Xiao-dong
2013, 34(1): 90-94.
When a method based on linear model is applied for motion-blurred image restoration, its least square solution is the best linear unbiased estimator for the restoration. Because of the ill-conditioned degeneration of the image, this solution always diverges far from the original value in the case of noise jamming. In order to overcome the shortage, some subspaces not susceptible to noise were extracted by singular value decomposition (SVD) of degenerate matrix. A more robust inverse matrix was reconstructed on these spaces and it ensured the restored image had less distortion in a longer blurred length.
Optical Metrology and Measurement
Large convex mirror measurement by subaperture stitching interferometry
WANG Xiao-kun
2013, 34(1): 95-100.
On the basis of summing up conventional testing methods for convex mirror, a novel method for testing convex surfaces by subaperture stitching interferometry (SSI) was proposed. A sphere mirror is used as the reference surface, the phase distribution of each subaperture can be measured by the digital wavefront interferometer, and the full aperture surface map can be calculated by stitching several subapertures. The basic principle and theory of SSI were researched, and the stitching processing and prototype for testing convex spheres were devised and developed. A convex SiC sphere with the aperture of 300 mm was tested by SSI with 9 subapertures. For the validation, the sphere was also tested by large interferometer and beam expander, and the peakvalley(PV) and root-mean-square(RMS) residual errors between them were 0.102 and 0.009 , respectively(=632.8 nm).
High-precision measurement of turret dynamic angle based on capacitive encoder
YU Xun, MA Lin, LIU Xue-song, HAN Feng, XUE Xiao-le
2013, 34(1): 101-104.
Capacitive encoder is a novel sensing technology developed from the traditional capacitive technique. Aiming at the high-precision testing requirement of the relative angle between the turret and its chassis, a high-precision measurement method of turret dynamic angle based on capacitive encoder was proposed. In view of the turret environment, the installation method of the capacitive angle measurement was designed and the working principle was analyzed. With the design of the mechanical structure and the subsequent circuit, the system stability and reliability of the capacitive encoder were improved. Laboratory angle calibration and field range experiments for angle measuring device were carried out. Results show that the system which obtains the function of power protection, location identification and zero-memory can meet the actual demands and the measurement accuracy is up to 60.
Testing optical system with high NA based onphase retrieval
SHAO Jing, MA Dong-mei
2013, 34(1): 105-110.
The interferometric method has been widely used in wavefront sensing of optical systems, however, manufacturing a reference objective with high numerical aperture (NA) has high production costs and risks. The optical interferometric method used in wavefront sensing of the optical system with high NA meets trouble. Using the phase retrieval method, a wavefront testing for optical system with high NA was done and diffraction beam from a pinhole was used as an ideal testing wavefront. The point spread functions (PSF) of wavefront with different frequencies were simulated, and the actual condition need was analyzed. A novel way was introduced into the error analysis, due to the lack of high accurate contrast verification. Wavefront sensing of a microscope optical system has been completed. Through this confirmatory experiment, its results verify this method.
Improving data update speed of star sensor
LUO Chang-zhou, WANG Jie, SHAO Lei, YAN Jun, WANG Sheng-nan, ZHAO Guang-zhou
2013, 34(1): 111-116.
Star sensor is one of the key instruments in the celestial inertial navigation system (INS/CNS), and measuring period or update speed is one of the important specifications of it. To satisfy the practical requirements of INS/CNS, the main aspect influencing the data update speed was discussed. A new method was proposed, which made the data acquiring procedure and data processing procedure executed synchronously by arranging subtask reasonably to improve the data update speed of star sensor. The hardware and software of the electronic system which adopted the method were designed properly, and the data update speed of the star sensor was improved from 3.70 Hz to 6.40 Hz, which met the system demand.
Surface inspection and evaluation of ellipsoidal mirror using 3D scanning
LiuShao-bo, WANG Yin-he, LEI Peng, YAO Chun-long, GAO Peng, YIN Xiao-jun
2013, 34(1): 117-122.
By using 3D scanning detection method, we measured the surface of ellipsoidal reflector and performed the best fitting contrast with the standard ellipsoidal suface-taking E210 reflector as an example. The result shows that the 3D scan detection method is capable of ellipsoidal reflector inspection, and the E210 ellipsoidal reflector is processed excessively on the bottom and insufficiently on the top in an approximate shape like cross. The processing error is -0.06 mm~+0.08 mm, which meets the limited profile error range of -0.1 mm~+0.1 mm. We carried out the reverse calculation according to the scanned point cloud data and established an actual reflection surface model, moreover, further simulation of reflector parameters, such as reflecting spot shape and size, was accomplished. The simulation results correspond well to the test result.
Rock mechanical behaviors testing by digital speckle correlation method
MI Hong-lin
2013, 34(1): 123-127.
Rock subjected to external force can produce deformation. Discovery and knowledge of the deformation information and stress distributions of rock play important roles in warning and avoiding the catastrophic failure. Digital speckle correlation method (DSCM) was used to measure the deformation, stress and strain of rock material by non-contact mode. In order to verify the validity of the experimental results, electronic resistance gauge (ERG) was adhered to the near picking area and the experiment results and ERG results agreed well. Through studying the mechanical behaviors of rock by DSCM, it indicates that DSCM technique can be used to measure the deformation of rock and forecast deformation information. The results can be given by quantitative or qualitative method.
Optical Element and Fabrication
Influence of UV irradiation on optical property of TiO2 thin film
PAN Yong-qiang, BAI Tao, TIAN Yu-jun
2013, 34(1): 128-132.
The TiO2 thin films were prepared by electron beam evaporation with different craft parameters, and the optical property of thin film with ultraviolet (UV) irradiation were studied by using ellipsometer and spectrophotometer. The results show that the refractive index of TiO2 thin film decreases with different craft parameters after the same UV irradiation, and moreover, the variation of the index increases with the raise of the deposition rate and the substrate temperature, as well as the decline of working pressure. The transmittance of thin film declines after radiation. With the same craft parameter, the refractive index declines rapidly first and then increases along with the radiation time, however, it is always less than the initial refractive index.
Design and fabrication of eye-safe laser ranging andinfrared imaging filter film
WANG Li-rong, SHI Peng, LI Hua-jie
2013, 34(1): 133-137.
From the viewpoint of eye-safe, a filter film with 1 550 nm for laser ranging and 3 m~5 m spectral band for infrared imaging was designed and fabricated to inhibit 1 064 nm laser. In order to improve the mechanical strength of filter film, the thickness of every film layer was limited and the layers were reasonably arranged. ZnS and YbF3 were used as the materials and multi-spectral ZnS was used as the substrate. The filter film was fabricated by the electron beam deposition technique. Ion assisted deposition and vacuum annealing techniques were used to improve the stability of filter film. The result of spectrum measurement shows that the transmittance is only 0.5% for 1 064 nm laser and 99.3% for 1 550 nm laser, and the average transmittance is more than 99.6% for the range of 3.5 m~3.9 m. Although the refractive index of YbF3 increases in the process of deposition, the spectrum curve is not severely impacted. Environmental reliability tests were finished and results prove that the filter film is tolerant of harsh environment and can meet the requirement.
Application of novel film image reader
ZHANG Xiao-ling, KANG She-feng, ZHU Xin-hong, SONG zhe
2013, 34(1): 138-142.
Aiming at the low level automation and lots of human factors in the measurement and processing of slit film parameter, we introduced a novel film image reader. The light source irradiated the material to be scanned to complete the image acquisition and irradiated the CCD to achieve photoelectric conversion. The slit photographic film images were digitized and processed using software. The results show that the reader realizes large format (830 mm190 mm)color film image input. The platform structure and the precision of the transmission system ensure the all format precision of less than 0.1 mm, which is the measurement requirement, it can improve the automation of the film image reader, as well as the accurate measuring and processing of data.
Electro-optic characteristic of liquid crystal
JIN Peng-fei
2013, 34(1): 143-147.
With the wide application of liquid crystal display technique in most fields and the promotion of new technologies in recent years, much endeavor has been made to improve its performance. The photoelectric characteristic is an important parameter in the application of liquid crystal devices. The electro-optical properties, threshold voltage and viewing angle of liquid crystal were studied by using laser measurement, and the distortion characteristics of liquid crystal molecules affected by the alternating electric field after re-orientation were analyzed. The twist angle of liquid crystal molecules and transmittance under different voltage conditions were also tested. The results show that this method is feasible. The twisted nematic liquid crystal has 0.92 V lower threshold voltage and relatively steep electro-optical curve, and it possessed good view angle properties from -60 to +50 in the horizontal direction and from -40 to +20 in the vertical direction. The conclusion provides scientific basis for the design and manufacture of polarizer.
Laser Technology
High precision micro energy laser calibration technology
LI Gao-ping, LIU Guo-rong, LI Si-wei, YIN Wan-hong, YU Dong-yu
2013, 34(1): 148-151.
A chopper was used to change continuous laser into microsecond repetition-rate pulse width laser, then a single pulse chooser was used to make a single pulse laser from the repetition-rate laser. A trap detector was used to measure the output power of the continuous laser. Besides, the high-speed APD probe and high-gain PIN probe were used to detect the waveform of the pulse laser waveform, and the oscilloscope was used to measure the width of the pulse laser. Based on the measured power and waveform, the pulse laser-s energy could be obtained. Using this method, the 0.2 pJ micro energy laser measurement and calibration could be realized. Through analysis, the measurement uncertainty of the device reached 0.42%.
LD side-pumped Nd∶GdVO4 532 nm green laser
MAO Xin, SHEN Zhao-guo, FU Jie, TANG Gang-feng, YANG Yi, CHENG Jian-xin
2013, 34(1): 152-155.
To acquire high-power narrow-width 532 nm green laser,we used the acousto-optic driving Q-switched synchronization technology with high repetition rate and the laser diode (LD) side-pumped Nd∶GdVO4 laser to get high-power linearly polarized 1 064 nm laser output. We achieved high-power green laser output by intra-cavity frequency doubling and KTP non-linear frequency conversion. As the input current was 30 A and the Q-switched frequency was 10 kHz, we got the 1 064 nm polarized laser output with maximum power of 30 W and narrow width of 30 ns, and the 532 nm green laser output from KTP crystal with the maximum power of 23.4 W. Conversion efficiency of 1 064 nm to 532 nm was 78%. Experiment results indicate that the acousto-optic Q-switched technology and LD side-pumped Nd∶GdVO4 laser in tandem technology can be used to obtain high repetition frequency 1064nm polarized laser, and the high-power 532 nm green laser can be output by KTP non-linear frequency conversion.
High repetition rate PPLT eye-safe laser with 1.06 μm pumping
FU Jie, SHEN Zhao-guo, TANG Gang-feng, MAO Xin, CHENG Jian-xin, YANG Yi
2013, 34(1): 156-160.
A 1.54 m laser was obtained using periodically poled lithium tantalate (PPLT) crystal pumped by 1.06 m laser. Intracavity optical parametric oscillator(OPO) was adopted and parameters of resonant cavity were optimized by using V-type cavity. The change of the beam spot along with the thermal focus length of gain medium and the impact of the angle of V-type cavity on beam quality were analyzed. As the input electric power was about 100 W, the 1.54 m laser with the repetition rate of 10 kHz, pulsewidth of 125 ns and average power of 1.9 W was acquired, and the electro-optical efficiency of 1.9% was achieved.
Research and improvement of path length controlconfiguration for laser gyroscopes
LAN Pei-feng, LIU Yuan-zheng, WANG Ji-liang, ZHANG Ming-hui
2013, 34(1): 161-165.
Path length control configuration for ring laser gyroscopes (RLGs) maintains the stability of frequency of beams through controlling the path length, which is very important to improve the performance of RLG. Aiming at the deflection of beams in working RLG caused by the distorted control mirror in traditional path length control configuration, which leads to dispersion and changes of loss to affect the performance and precision of RLG, the path length control configuration for RLG was researched and a new path length control configuration which could reduce the effects of distorted control mirror on RLG was designed. Moreover, the simulation and optimization on the new path length control configuration were done with the direct coupled field analysis of the finite element (FE) method. Results show that the new path length control configuration reduces the distortion of the control mirror, improves the performance and precision of RLG, the zero-bias stability is increased from 0.7/h to 0.3/h.
Application of large-current constant-power dischargetechnology in high power DPL
QI Yuan, WANG Liang, LI Gang, ZHANG Biao, YANG Ai-fen
2013, 34(1): 166-169.
According to the special requirements of high-power diode pumped laser (DPL) for high-power driving power, we put forward a particular discharge and driving control circuit based on large current and constant power. We designed a suit of laser diode (LD) array driving power supply by combining the existing charging circuit with the over-current protection circuit, and applied it to DPL system which was based on high-power LD array. Through electrical properties and relevant experiment, it is proved that this power can provide a more than 200A driving current with the pulse width of 230s and the frequency of 20Hz for DPL.It has important value for kinds of DPL-based laser weapon systems in practice.
Operating range of laser unit for carrier landingbased on opto-electronic guidance
BAI Bin, WU Wen-hai, QU Zhi-gang, FAN Hai-zhen, WANG Qi
2013, 34(1): 170-175.
The working principle of laser ranging/tracking unit in opto-electronic landing guidance was expounded. The laser emitting waveband was discussed and determined from the two main factors, eye-safe and atmosphere-window. The 1.5x m laser-s atmosphere transmittance was studied by comparing the results of empirical formula calculation and MODTRAN experiment. Based on the outcome of the precise calculation of atmosphere transmittance, the operating ranges of the laser unit under different meteorological conditions were analyzed. Results show the maximum operating ranges of the laser unit are 10.8 km and 8.5 km respectively in clear and haze conditions, which meets the requirement of opto-electronic landing guidance system for the tracking distance of more than 6 km.
Fiber Sensing and Optical Communication
Factors affecting all-optical clock recovery performance based onfiber-optical parametric oscillators
WEN Feng, WU Bao-jian, LI Zhi, LUO Te, ZHOU Xing-yu
2013, 34(1): 176-181.
The factors influencing the phase jitter and amplitude noise of clock signal extracted by the fiberoptical parametric oscillator (FOPO), such as the modulation rate, pump power and polarization state of the input signal and the fiber length, polarization rotation in the FOPO cavity, were experimentally investigated. Experimental results show that, the all-optical clock recovery based on the FOPO can handle the variation of 8.2 kHz modulation rate, 5 dB pump power, 20 azimuth of pump signal, 2 mm cavity length and 14 signal azimuth in the cavity when the root-mean-square (RMS) phase jitter of clock signal is less than 0.025 UI. It helps to further improve the performance of all-optical clock recovery based on FOPOs.
Absorption efficiency of double-clad fiber based on Zemax
MA Hai-xia
2013, 34(1): 182-187.
In order to calculate the absorption efficiency of different doubleclad optical fibers, twodimensional analysis, threedimensional analysis and fiber optics wave coupling theory were adopted in the past. A 3-D method based on Zemax software was introduced in this paper, the absorption efficiency of circular, offset, rectangular, D-shape, octagonal double-clad fibers were investigated by writing ZPL macros, and the results were compared with the data obtained from the 2-D analysis. Data showed that two results were similar and the absorption efficiency trends of different inner-clad fibers were same. The solution based on Zemax had many advantages in comparison with the 2-D analysis. The simulation based on Zemax was more vivid because the relationship between the absorption efficiency and fiber length could be achieved, however, the relationship between the absorption efficiency and reflection times was obtained based on the 2-D analysis. The critical angle could be set in Zemax, rays with arbitrary angle were emitted from the arbitrary point in the inner-clad section in the 2-D analysis ignoring ray total reflection condition in the inner-clad, so the result based on Zemax was more accurate. It was easy to simulate the different inner-clad shapes and the non-sequential ray tracing velocity was very fast, the operation time based on Zemax was 373 seconds, and was 1 732 seconds based on 2-D analysis under the same condition for the same rectangular inner-clad fiber,so the calculate speed based on Zemax was more rapid. The absorption efficiency of a new structure double-clad fiber put forward by professor LOU Qi-hong was calculated finally.
Application of Kalman filter based fiber opticgyroscope in airborne electro-optical system
LEI Fei-lin, LIU Jian-wei, WU Yu-jing, ZHAO Chuang-she, SANG Wei, WANG Xin-wei
2013, 34(1): 188-192.
Due to the high output noise and the random drift of fiber optic gyroscope (FOG) which bring on low dynamic performance of airborne electro-optical (E-O) system, the mea-sured data of FOG output in system was analyzed. According to the noise feature, the AR2 model of FOG was established. And a method of the Kalman filter based FOG in airborne E-O system was studied. Compared with the traditional moving average filter, the results of experiment were displayed. The results show that the high frequency noise can be filtered, and the random drift is restrained. Also the dynamic performance of system is improved effectively. These results provide reference values for the applications of FOG in airborne E-O system.