2011 Vol. 32, No. 5

OE System and Engineering
Catadioptric omnidirectional system with undistorted imaging
FAN Zhi-Gang, WANG Fang-Bo, CHEN Shou-Qian, FENG Li-Tong
2011, 32(5): 817-821.
A catadioptric system uses a combination of lenses and mirrors placed in a carefully arranged configuration to capture a much wider field of view. However, images obtained by using a single-viewpoint catadioptric omnidirectional system have a large amount of visual distortion. To design a catadioptric omnidirectional system with undistorted imaging, appropriate surfaces were presented. The surfaces preserved a linear relationship between the angle of incidence of light onto the surface and the angle of reflection onto the imaging device, as does a normal mirror. The reflective mirror and the lens were designed for a catadioptric omnidirectional camera with the F number 3.3 and the field of view 138. The modulation transfer function is better than 0.6 at 66.7 lp/mm and the distortion is less than 4% over the whole active area of the image sensor. The deduction of the reflective surfaces offers an essential model and a computing method to design a catadioptric omnidirectional system with undistorted imaging.
High precision electro-optical ballistic measurement system
SHOU Shao-jun, LU Pei-guo, LIU Jing-li, LIU Xiao-qiang, XING Jun-zhi
2011, 32(5): 822-827.
Electro-optical tracking systems are widely used to make the real-time measurement of flying targets in test field due to their capabilities of tracking high speed targets precisely, as well as providing flight path data and flight attitude image in real time. A novel vehicle-borne electro-optical trajectory measurement system is presented. Rigid bearings were used to improve the stability of angular position output. Regenerative feedback technology was applied to suppress lagging error when a high-speed target was tracked. Measurement data with 20 ms update rate were normalized to rectangular coordinates to make data analysis conveniently. Besides, a simulated trajectory detection method to test system in the field is put forward. The system is flexible to be deployed and is able to measure trajectory of flying target promptly and precisely. The steady-state tracking accuracy can reach 0.21 mrad.
Low F# digital X-ray radiography system
CHEN Bao-ying, TANG Yong, CHAI Li-fei, SUN Hao, ZHANG Yuan-jian, LIN Sen
2011, 32(5): 827-830.
An optical system of digital X-ray radiography based on CsI scintillation screen with 60 mm45 mm dimension for dental diagnosis was designed. A CCD with a 4.8 mm3.6 mm image surface was selected. The lens system had a complicated double-Gauss configuration. The F# and full field of view were up to F/0.9 and 35 respectively, the focal length was 9mm. The results showed that the modulation transformation function of full field of view was greater than 0. 75 at the spatial frequency of 56 lp/mm, the distortion of full field of view was 1.8%, and the relative illumination reached 80%.The aberrations of the whole system were corrected, which met the requirements for the digital X-ray radiography system.
Influence of transducer bandwidth on photo-acoustic imaging resolution
TAN Yi, HUANG Xin-min, REN Ya-jie
2011, 32(5): 831-834.
In order to research the influence of different bandwidths of transducer on photo-acoustic imaging resolution, finite element simulation experiments were carried out. An empirical formula was obtained between transducer bandwidth and photo-acoustic imaging resolution. Experimental results showed that the reconstructed image resolution of absorbers was unchanged in the order of millimeters when the cut-off frequency of transducer was greater than 2 MHz; however, it was contrary for the frequency less than 2 MHz. The results are helpful for the choice of transducer and the evaluation of image reconstruction.
Airborne cube corner retro-reflector array
LI Jian-chao, GAO Ming, SU Jun-hong
2011, 32(5): 835-839.
Dome-like structure are extensively used in low-orbit target and it has the disadvantages of small remote angle and large blind zone. Based on the research of the cube corner prism and the allowable variation range of incident angle, we designed a airborne laser retro-reflector device with a dimension of -119 mm88.8 mm, composing of 15 cube corner prisms. The undersurface of the cube corner retro-reflector was cut into regular hexagon with 15.5 mm side length and 26.87 mm distance of opposite edges. The clear aperture and the height of the cube corner are 25 mm and 19 mm respectively. Considering the effect of speed difference and compensation requirements, the designed maximum angle error of cube corner retro-reflector was 5, and the maximum error of surface profile was 5. Compared with the single-layer corner reflectors, the allowable range of incident angles was increased and the blind zone of loworbit target was reduces significantly.
Folding dual-band imaging system with controllable exposure
CHENG Lei, HE Jun-hua, YAN Ya-dong, LU Wei-tao
2011, 32(5): 840-844.
A folding 1∶1 imaging system with switchable waveband and controllable exposure time of 0.1 s~99.9 s was designed. In this system, the front and rear lens groups were connected through a deflection prism, the color filter was changed to achieve dualband imaging, and the high resolution folding lens was coupled with electronic shutter to control the exposure time. The field of view of the optical system was 17 mm, the resolution was enhanced to 8 m,and the working distance reached 55 mm. The results showed that the exposure time and the direction of light could be accurately controlled. The optical system is flexible, costefficient and can be adapted to different lenses according to different requirements in chemiluminescence immunoassay, environmental science and photochemistry.
38× zoom ratio wideband TV lens optics
HU Ji-xian
2011, 32(5): 845-848.
According to the characteristics of large FOV high zoom ratio wideband optical system, a 38 zoom ratio was designed, the primary and advanced aberrations of large FOV wideband system were balanced by using the mechanical compensation technique of changing root, the h-hp diagram and the aperture diagram analysis. A method using the cam formula to calculate the displacement of compensation group with no parfocality by programming and modify the design value of cam curve in Code V was put forward. This method ensured the parfocality of the high zoom ratio optical system.
Design and implementation of north-finding commander sight for tank and armored vehicle
DENG Hong-lin, GUO Shuan-yun, HU Yu-shu, LI Zhang, LIANG Qing-qian, ZHOU Guo-liang
2011, 32(5): 849-853.
A north-finding commander sight for tank and armored vehicle was designed. It adopted two fiber optic gyros and two accelerometers to realize inertial measurement and gyro information was shared by both north finding and line of sight (LOS) stabilization. The control process and combined algorithms were designed. While ensuring a high accuracy of the commander sight LOS stabilization, it performed north finding in any position when the vehicle azimuth platform was unleveled. The north-finding method was that the commander sight rotated to four fixed positions and stopped for an interval at these positions, these intervals are used to sample and store data at the four positions. After the completion of four-position rotation, the recorded data were combined, filtered and calculated to obtain the north-finding result. The concept design, implementation approach and derivation approach were discussed. The demonstration test proves that the desired specifications are achieved.
Encoding multiple objects in computer-generated holograms with synthetic spectrum
GUO Rong-li, LU Shao-jun, HAN Jun, YU Xun, HOU Rui-ning
2011, 32(5): 854-859.
A method for encoding multiple objects by using the synthetic spectrum in Fourier transform computer generated holograms (CGH) of detour phase is proposed. The method allows multiple objects encoded in a CGH using synthesized spectrum instead of single spectrum used in conventional method. In reconstruction, multiple objects are reconstructed around the same diffraction order simultaneously, and various forms of reconstructed images are obtained easily. Optical reconstruction of the CGH was demonstrated with a liquid crystalspatial light modulator (LC-SLM). The experiment result verified the effectiveness of the method and it showed that the method could improve the information capacity of CGH.
Zoom lens system of stage lighting with LED array
WANG Hong-yin, ZHANG Jun, CHEN Zhe, ZHOU Dong-hua
2011, 32(5): 860-866.
Aiming at the problems of the unchangeable beam angle and the low light utilization efficiency of the domestic high-power LED array stage lighting, a zoom lens system with array source was designed. Firstly, a zoom lens group with single LED source was designed with 18.5~38.7beam angle (1/10 peak angle ) when the focal range was 0mm~10 mm, and the light utilization efficiency was more than 78% when focal length was 10 mm. Secondly, the zoom lens group with single LED source was extended to a zoom lens system with 36 LED sources (12 red LEDs, 12 green and 12 blue), the beam angle and the color blending effect were analyzed at different arrangements of LED array. The results show that with the same focal range as the single LED, the beam angle range (1/10 peak angle) is 21~38.6, and the more uniform the arrangement of different color LED is, the better the color blending effect is. Compared with the existing domestic highpower LED stage lighting, this new zoom lens system has improvements in both beam angle and light efficiency.
Resolution of micro-stereo-lithography system using high viscosity nanocomposites
ZHOU Geng-xia, BAN Shu-bao, SUN Tian-yu, GU Ji-hua, WU Dong-min
2011, 32(5): 867-871.
To fabricate microstructures using high viscosity composites, an integral stereo-lithography (SL) system adopting a digital micro-mirror device (DMD) as its dynamic mask was developed, which employed our novel resin vat and coating system. It shows that the lateral resolution of the SL system is determined by the optical resolution and the chemical response of the photo curable resin, the lateral resolution of the SL system is decreased as the curing depth goes beyond a critical value. The measured values of the optical system-s resolution and the resin-s working curve indicate that the maximum lateral resolution of the SL system is 14 m.
OE Information Acquisition and Processing
Scanning modulation transfer function analysis of push-broom linear TDI CCD
YANG Yong-ming, LI Xin-yang, ZHAO Jia-xin
2011, 32(5): 872-877.
Scanning modulation transfer function (MTF) for linear time-delay integration (TDI) charge coupled device (CCD) using push-broom imaging mode was established. The MTF which took the discrete sampling characteristics of linear TDI CCD into account, was based on the imaging modulation mean within sampling interval. The numerical analysis of the proposed MTF indicated that the value of MTF at Nyquist frequency for linear TDI CCD with 10 m pixel size was 0.363, 0.333 and 0.255 respectively, when the number of row transfer phase clocks was 4, 3 and 2. When the row frequency error was 1% or 3%,the changes of MTF curves with different integration numbers implied that increasing the row frequency error and the integration number could decrease the value of MTF and reduce the image resolution. The results of imaging experiment agree with the quantity analysis of the proposed MTF.
Phase error correction in Fourier transform spectrometer based on phase correlation
WANG Cai-ling, LI Yu-shan, LIU Xue-wu, HU Bing-liang
2011, 32(5): 878-882.
Phase error correction (PEC) is an important step during hyperspectral data processing of the Fourier transform spectrometer. We present a new method for phase correction of the Fourier transform data according to the symmetry of interference curve and the calculation of phase correlation method. The phase correlation is fitted to Sinc function, the sub-pixel offset is calculated, and the interference curve is converted into spectral domain through discrete cosine transform (DCT). The interference data simulated by DCT is compared with the data by Mertz method, and the results shows that the proposed method has higher correction accuracy than Mertz and simple calculation.
Comparison of algorithms for filtering speckle noise in digital holography
PAN Yun, PAN Wei-qing, CHAO Ming-ju
2011, 32(5): 883-887.
In the recording process of digital holographic measurement, the hologram is easily polluted by speckle noise, which may decrease the resolution of the hologram. In addition, the reconstructed effect is seriously affected by speckle noise in digital reconstruction. Thus it is important to study the filtering speckle algorithms for digital hologram. The median filtering algorithm, Lee filtering algorithm, Kuan filtering algorithm and SUSAN filtering algorithm were introduced to filter the speckle noise in hologram and reconstructed image. Then these algorithms were compared. The results showed that the SUSAN filtering algorithm was better in digital holographic technology. The speckle noises were suppressed significantly and the information of reconstructed images were well maintained.
Dwell time algorithm of synthesis for ion beam polishing
GUO Wei-yuan, CHENG Xian-kai, LIANG Bin
2011, 32(5): 888-893.
In the process of ion beam polishing, the determination of dwell time is very crucial. Usually the ideal Gauss function is used to approximate the practical processing function. If the practical processing function is used to simulate processing, the result of processing is not satis-facotry. A synthesis algorithm of coefficient method and elimination method is proposed to improve the accuracy of mirror face when the practical processing function is adopted to simulate processing. Firstly, it uses the coefficient method iteratively to get a smooth mirror face, and then uses the elimination method to improve the accuracy. This algorithm runs faster, and works out a smooth mirror face with high accuracy. The synthesis algorithm is simulated, the results between the ideal Gauss function and the practical processing function are compared, as well as the mirror faces obtained by elimination method and synthesis method. The simulation results show that, compared with the 83.36 nm PV value of the practical processing function without the synthesis algorithm, the one with the synthesis algorithm is decreased to 46.92 nm, and the accuracy of mirror face is improved.
Two analytical reconstruction algorithms for spiral cone-beam computerized tomography
WANG Bo, XUE Ying, YU Hui-tian
2011, 32(5): 894-898.
The Katsevich and FDK reconstruction algorithms for cone-beam spiral scan were studied and compared. The results showed that FDK algorithm and Katsevich algorithm obtained good results when the projection data did not contain noise; however, when the Katsevich algorithm was used to compute the derivative of the projection data containing noise for the reconstruction of actual object, the reconstruction quality declined because this algorithm was sensitive to the noise of projection data.
Transmission characteristics of high-birefringence Sagnac loop filter
LI Hai-lan, WANG Yan, ZHANG Xing-jiao, YE Zhi-qing
2011, 32(5): 899-903.
Transmission characteristics of a high-birefringence Sagnac loop was studied by using transfer matrix method, numerical simulation and experimental investigation. The Sagnac loop filter was composed of an optical coupler (OC), a polarization controller (PC) and polarization-maintaining fiber (PMF). The influence of PMF characteristics and PC state on transmission characteristics of Sagnac loop was theoretically analyzed. The transmission spectra of different PMFs, birefringences (n) and PCs state were obtained through numerical simulation. The experiment was done and the results indicated that the wavelength spacing was determined by PMF length and birefringence (n), the transitivity by PC state and transmission peak by PMF and PC state. The experimental results agreed with the theoretical analysis.
Human body limbs detection algorithm based on integral image
CHEN Hua, HU Chun-hai
2011, 32(5): 904-908.
The method based on the integral image and the haar-like feature for detecting body limbs is proposed for video images. Haar-like feature is suitable for detecting rectangular or rectangular-like image areas because of its inherent characteristics, and the integral image can quickly locate the body by the haarlike feature in the image. The integral image is the original image for video. After edge detection template is convoluted with each frame of the original video, they are added to obtain the integral image. The body physical location can be calculated by the integral image and using haar-like feature according to the set threshold. The experiment results show the algorithm is better than the background subtraction.
Optical Metrology and Measurement
Surface roughness measurement based on non-diffracting beamtriangulation and grey evaluation
WANG Zhong-yu, WANG Qian, MENG Hao, WANG Xue
2011, 32(5): 909-912.
Laser triangulation method is normally used in the non-contact precision measurement of surface topography due to its simplicity and robustness. In the traditional laser triangulation method, a Gaussian beam is used to scan the measured surface point-by-point. Since data collecting is completed with point scanning, a large number of measurements are needed to obtain the surface topography of the whole surface. Taking non-diffracting light as the incident light of the laser triangulation measurement system, the non-contact precision measurement for surface roughness is fulfilled with a higher speed and it solves the focal depth problem of the Gaussian beam. The evaluation method of the surface roughness based on the grey filtering overcomes the shortages of the existing evaluation methods and is complementary to Gaussian filtering method. The measurement results show that the system measures the surface roughness accurately and the proposed grey evaluation method is effective.
Measurement principle of six-light-screen vertical target based on sky screen
DONG Tao, NI Jin-ping
2011, 32(5): 913-916.
In order to measure the projectile velocity and the target coordinates in any incident direction simultaneously, a concept of six-light-screen vertical targets based on sky screen was presented. Six detection screens were formed in space by six sky screens. When the projectile passed through the six screens in turn at an angle, the time intervals of projectile passing through the six screens were measured by the signal acquisition and processing system. The projectile velocity,incident angle and target coordinates were calculated according to the intervals and structural parameters. The measurement principle and the formulas were given, and the measurement error was analyzed. The results show that the concept is precise and easy to be engineer implemented.
Multi-spectral axes parallelism calibration of electro-optical system
MA Shi-bang, YANG Hong, YANG Zhao-jin, GUO Yu, KANG Deng-kui
2011, 32(5): 917-921.
Several bore-sight methods for multi-spectral optical axes used nowadays were compared. Based on a large aperture collimator, a new bore-sight method for optical axes parallelism was put forward by using CCD technology. In this method, the ZYGO interferometer was used for accurately focusing. By comparing the center coordinates of the conjugated image on CCD of the target with the center coordinates of the laser spot of the system under test, the parallelism between the visible axis or infrared axis and the laser axis was calculated. The focal plane of large aperture off-axis paraboloid was determined and analyzed, and the center position of the laser spot was determined as well. The measurement uncertainty was analyzed and the uncertainty of 5 was obtained.
Impact of illumination on image detection accuracy
TIAN Yuan-yuan, TAN Qing-Chang
2011, 32(5): 922-925.
Light source is critical for photograph quality. Experiments with different illumination methods and light sources were conducted. Firstly, a photo of normal cube with CCD camera was taken. Secondly, iterative average filter method was used to deal with image collected to reduce interference caused by noise in detecting edge. Thirdly, 1D gray moment sub-pixel method was used to detect edge of normal cube. Finally, average algorithm was used to calculate thickness of every normal cube to test the impact of illumination system on image detection accuracy. The test shows that illumination error of apheliotropic light for medical observation is the minimum.
In-flight calibration of atmospheric wind and temperature measurement spectrometer
SHI Da-lian, BAI Qing-lan, FENG Yu-tao, WEN De-sheng
2011, 32(5): 926-930.
The atmospheric wind fields and temperature fields are important atmospherical parameters. The atmospheric wind and temperature measurement technology was already developed in many nations for years, and there is increasingly demanded in China now. Atmospheric wind and temperature are measured by the spectrometers of high spectral resolution, which detects the Doppler line shift and expanding of the special spectrum line in the atmosphere. The in-flight calibration technology is critical for high resolution measurement of the atmospheric wind. Several typical atmospheric wind measurement spectrometers are reviewed, analyzed and summarized. The in-flight calibration technology used in these spectrometers is given.
Angle measurement based on optical polarization beam imaging
JIANG Qi, XU Gui-li, LI Kai-yu, TIAN Yu-peng
2011, 32(5): 931-936.
In order to measure the rotation angle and the distribution of polarized light in optical rotation effect accurately, a new method based on polarization beam imaging is proposed. The theory of the rotation angle of field measurement is reviewed and the system of photoelectric detection is designed. With a polarized beam splitter, the light is split into S light and P light which are acquired by a high resolution CCD. The image is filtered by a median filter, the matching processing based on singular value is implemented, and signal processing is used to eliminate the source fluctuations. The results show that it can detect the two-dimensional distribution of rotation angle from the light source fluctuation rapidly and accurately, and the standard deviation is only 40% of the traditional measurement methods.
Real-time spectrum measurement in thin-film thickness wideband monitoring system
SHANG Xiao-yan, HAN Jun, LI Qi, WANG Song
2011, 32(5): 937-941.
In a thin-film thickness wideband monitoring system, a grating spectrometer is utilized to disperse spectrum and the linear CCD is used to quickly finish spectrum scanning to control the thin-film thickness, which satisfies the requirements of the real-time monitoring. However, the accuracy of spectrum scanning directly affects the availability of the thin-film thickness real-time monitoring. In order to obtain precise spectrum information, the corresponding relationship between CCD pixel and spectral wavelength was determined. Based on the discrete relationship between characteristic spectral lines and pixels, the spectrum calibration function was established using the least-square fitting method, and the root-mean-square error of calibrated wavelength was 0.037 nm by experiment. Then aiming at the spectral monitoring signal from CCD output in real-time, the wavelet threshold filtering optimization algorithm was applied to suppress the random noise and the spectrum signal details were well reserved, the maximums of peak error and peak location error were 1.0% and 0.3% respectively, which satisfied the spectral resolution requirements.
Uncertainty analysis of laser calorimetry
LIU Hao, MA Ping
2011, 32(5): 942-948.
Based on a laser calorimetry instrument, the error source of the measurement or uncertainty of weak absorption were analyzed with the exponential method, pulse method and gradient method given in ISO 11551. The uncertainties of the parameters such as mass and laser power were evaluated by B method, while the uncertainties of the parameters induced by fitting and residual errors were evaluated by regression analysis and calculated by MATLAB. A sample was picked up randomly to make measurement repetitively, proving the feasibility of the evaluation. It was revealed that the fitting error contributed notably to the uncertainty of absorption calculation. The relative uncertainty of exponential method was approximately 0.0129, and the uncertainty of the pulse method was 0.0029, proving that the pulse method was the best among the three. The gradient method adopted no more than 2 points in temperature data, and had a relative uncertainty about 0.0961. The promising way to increase the precision of calorimetry is to improve the data processing method and the laser power measurement.
Vision measurement for impact point
LIU Mei-lian, CAI Hui-min
2011, 32(5): 949-954.
Traditional vision measurement methods are not applicable for remote objects in large area. A simple vision measurement method is put forward to locate the remote objects in large area accurately. By using the simple calibration method, the transverse epipolar planes of the two cameras are horizontal and coplanar. On the basis of vision measurement principle, a simplified model of vision measurement for calculating the coordinates of impact point was built. And this model was used to locate the 44 object points in the whole field of view of the two cameras in 250 m350 m measurement area. Experiment data shows that the overall relative measurement error of this model is less than 0.3%,which is a good measurement accuracy.
Sub-pixel calibration of CCD in Moiré fringes measurement based on image processing
WU Ling-ling, WANG Xing, CHEN Jing, WU Ji-an, ZHANG Wei-guang
2011, 32(5): 955-959.
The measurement based on Talbot effect and Moir fringes is suitable for lens of long focal length. To get the focal length accurately, the width or slope coefficient of Moir fringes are essential parameters. The CCD calibration precision should be improved due to its significant impact on measurement accuracy. A CCD calibration is put forward. The grating is set as the self-reference to calibrate the equivalent length of CCD pixel. The calibration is presented based on image processing and Gauss curve fitting. The calibration accuracy is proved less than 0.1 pixel by calibrating the standard fringes generated by MATLAB. Finally, the CCD pixel is calibrated by grating and gauge block separately, the results show that the calibration method using grating is simple and precise.
LLL Night Vision Device and Imaging
Progress in Si-microchannel plates
HUANG Yong-gang, HUANG Ying, ZHANG Yang, LIU Hui, LI Guo-en
2011, 32(5): 960-966.
Based on the demands for high performance and green manufacture of microchannel plates (MCP), the development of alternative material to replace lead silicate glass MCP (LSG-MCP) has been intensively investigated. In the past 20 years, silicon MCP has achieved significant progress and become one of the most promising MCPs. The research progress on Si-MCP is summarized in substrate material, preparation, performance and application. The preparation of microporous array, the preparation principle and method of functional layer of microporous inner wall are discussed. Compared with the conventional LSG-MCP, the advantages and disadvantages of Si-MCP in preparation and performance were analyzed. Finally, the prospect of Si-MCP is presented for further development.
Optical Element and Fabrication
Analysis of impact factors on frequency distribution of optic surface
2011, 32(5): 967-970.
The precision optical system has increasingly tighter tolerance demand on optics for applications in science and industry. The detection and control of the frequency distribution of optical surface is a problem. Power spectral density (PSD) was used as a measure to characterize the frequency information about optical surface. The wavefront phase measurement data were transformed to the data in the system of polar coordinates by cubic spline interpolation, and the PSD-s ratio was calculated. The influence of the tool performance and its motion in computer controlled optical surfacing (CCOS) technique on the frequency distribution was analyzed. It was pointed out that the characteristics of frequency distribution could be efficiently controlled if the machining parameters were selected properly, which was validated by the manufacture process of a 670 mm diameter aspheric mirror.
Design and optimization of anti-reflection coating with the structure of one-dimensional rectangular groove phase grating
MA Zhi-bo, HU Man-li, LI Wen-hui, LIAO Chun-yan, ZHAO Pei
2011, 32(5): 971-975.
A kind of anti-reflection (AR) coating with simple structure applicable in visible bands was designed. The characteristics of the AR-coatings were investigated by using the effective medium theory (EMT). The antireflective characteristics of 4 different substrate materials were compared and the polymethylmethacrylate (PMMA) was chosen for substrate to analyze the influences of the duty cycle, etching depth, incident wavelength and incident angle on the reflectivity of the groove phase grating. A set of parameters in the visible waveband of light are given. The research results show that the reflectivity is less than 2% in the waveband from 0.4 m to 0.55 m at the incident angle less than 30; the reflectivity is less than 2% in the waveband from 0.4 m to 0.8 m at the incident angle less than 10.
Total-internal-reflection compound secondary optical lens design of LED illumination
2011, 32(5): 976-980.
Secondary optics are critical components of lighting emitting diode (LED) luminaries, which determine the optical efficiency and light distribution characteristics of luminaries. Based on Snell-s law, edge-ray principle, energy conservation principle and Etendue conservation principle, we investigated a design methodology using the numerical solutions of a set of first-order partial differential equations to obtain the X,Y coordinates of the total-internalreflection (TIR) compound surface. We established the corresponding relationship between the angle of LED emerging light and the coordinates of target points on the illumination plane. According to the corresponding relationship, we calculated the coordinates of the other points on the compound surface and fitted the points to the three-dimensional entity model by CAD. Then the three-dimensional entity model was imported into optical software to carry out the simulation. The results showed that a uniform rectangular facula on the road surface could be obtained by adopting TIR-compound secondary optical lens on LED.
Multi-variable gray spatial soliton in biased centrosymmetric two-photon photorefractive crystals
JI Xuan-mang, JIANG Qi-chang, LIU Jin-song
2011, 32(5): 981-986.
To study multi-variable gray spatial soliton in biased centrosymmetric two-photon photorefractive crystals based on the theory of gray soliton in centrosymmetric two-photon photorefractive crystals, we derived the expressions of the normalized envelope solution of the centrosymmetric two-photon multi-variable grey spatial soliton numerically and investigated the characteristics of soliton. The results show that the multi-variable gray soliton is obtained by the coupling of the multi-beams which share the same polarization, wavelength and independent of each other. When only one or two variables are involved, the multi-variable gray spatial soliton degenerates into centrosymmetric two-photon multi-variable grey spatial soliton or incoherently coupled soliton pairs. When the multi-variable gray spatial soliton propagates in biased centrosymmetric two-photon photorefractive crystals, all the components propagate stably.
Infrared Technology
Point target detection in infrared search system
CHEN Zhi-xue, LUO Bei-bei, KONG Peng, GONG Jing-zhu, WANG Qi
2011, 32(5): 987-991.
Aiming at the effective detection of low signal-to-noise ratio (SNR) point target and the analysis capabilities in clutter background, a template matching filtering method is proposed. The algorithm uses dynamic threshold processing of background gray values, suppresses the background adaptively. When the background is complex, the template matching filtering method for target detection is used to remove the large areas of residual clutter after background suppression, and the extraction of weak target is achieved. The experiment results show that the SNR can be better than 4 dB when the scene is complex,and the detection probability of point targets is increased.
Influence of laser parameters on jamming effectiveness of IR imaging system
CHE Jin-xi, WANG Dong, ZHANG Heng-wei, ZHANG Lei-lei, ZHANG Lei, DONG Ze-jun
2011, 32(5): 992-997.
Jamming effect of laser on IR imager is an interesting research subject in electro-optical countermeasure. Jamming experiment and analysis were conducted. A pulsed CO2 laser with the wavelength of 10.6 m was used, and the laser was reflected to a polysilicon 320240 uncooled focal plane array (UFPA) infrared thermal imager through a diffuse plate. By adjusting the laser energy density, frequency, wavelength and the size of laser spot, as well as analyzing the jamming image quality, the influence of laser parameters on jamming effect was studied. The results show that the jamming effect is improved with the increasing of energy, frequency, wavelength and size of laser spot. Moreover, the jamming effect proves the feasibility of the diffuseness jamming, which avoids the interference source becoming the bait of the laser anti-radiation missiles and provides a new tactical solution for laser jamming.
New MRTD model for range prediction of scanning thermal imager
ZHANG Peng, WU Ping, JIA Quan-tao, ZENG Hui
2011, 32(5): 998-1002.
This paper presents a method for predicting the minimum resolvable temperature difference (MRTD) of thermal imager based on the perceived threshold signal-to-noise ratio of the human visual system. According to the frequency spectrum theory and two-dimensional modulation transfer function of infrared thermal imaging system, combined with the concept of matched filter, the method describes the spatial frequency spectral function of 4 standard bars. After the 4 standard bars are modulated and transferred by the infrared thermal imaging system, the perceived signal-to-noise ratio of the human visual system can be researched by using the spatial frequency spectral function. A new MRTD model based on the perceived threshold signal-to-noise ratio of the human visual system was established. The visual range prediction of thermal imager was achieved based on the MRTD model and visual range model. Simulation results show that the predicted visual range agrees with the experimental data.
Laser Technology
Wave plate phase retardation measurement on contact block based on optical feedback
LI Hao-hao, ZHANG Shu-lian, TAN Yi-dong, LI Yan
2011, 32(5): 1003-1008.
A technique to measure the phase difference of wave plate in the process of wave-plate production is introduced. It is based on the laser feedback method and achieves the on contact block measurement, which means to measure the wave plate when it is bonded on the contact block. On the basis of achieving on contact block measurement, we studied the stabilization of laser cavity length, the influence of the radius of feedback mirror and the optical contact bonding layer. The system reaches the measurement uncertainty of 1 and the measurement precision of 0.5.
Nonhomogeneity of end-pumped slab pumping beam and its improvement
LEI Cheng-qiang, WANG Yue-feng, HUANG Feng, HOU Jun-yan, YIN Zhi-yong, DUAN Xin-tao
2011, 32(5): 1009-1015.
Based on the non-sequential mode ray tracing of Zemax, light intensity distributions of pumped face and end surface in composite slab were simulated respectively. The tracing results showed that the light intensity distribution was homogeneous when the pumping beam was on the pumped face, however, the light intensity distribution was non-homogeneous when it was on the end surface after transmitting through the undoped crystal. The investigation results indicated that the propagation of pumping beam in the undoped crystal caused total internal reflection, which induced the overlap of pumping beam in partial region of end surface, and then induced the non-homogeneity of pumping beam distribution on the end surface. Finally, according to the planar waveguide homogenization theory, we put forward feasible techniques based on changing the length of undoped crystal and the divergence of incident beam to improve the pumping beam homogeneity, and carried out the simulation validation.
Laser scribing system for a-Si thin film solar cell preparation
XIAO Guang-hui, QIN Hai, LAN He, YE Jian, YANG Ming-sheng, PAN Long-fa
2011, 32(5): 1016-1021.
The laser scribing process for a-Si (amorphous silicon) thin film solar cell preparation requires the line width of 30 m~50 m, the dead zone of less than 300 m in size, and the compliance of line depth with the process requirements. Thus, the high beam quality of the laser is required, as well as the high imaging quality and wide focal depth of the optical system. A laser scribing system with a single laser and fourway light splitters was designed. With the designed laser scriber, a laser scribing test was done on a 1 400 mm1 100 mm3.2 mm glass substrate. The widths of the scribing lines P1, P2 and P3 were 35 m, 50 m and 45 m, respectively, the dead zone (distance between P1 and P3) was 287 m, and their final depths were 0.98 m, 0.24 m and 0.58 m respectively. The results show that the widths and depths of the scribing lines meet the requirements of thin film solar cell preparation process.
High resolution signal processing of mechanically dithered ring laser gyro
SU Rong-tao, HU Shao-min, FAN Zhen-fang, ZHOU Tian-yu
2011, 32(5): 1022-1026.
Two beat frequency signals with /2 phase difference are generated in mechanically dithered ring laser gyro (MDRLG). Usually the fourfold frequency counting signals are acquired when demodulating the two output signals. Finite impulse response (FIR) filtering and dither stripping are used to eliminate dither signal from the counting signals and obtain the angular rate of MDRLG. The analog beat frequency signals of MDRLG are sampled at a high speed and then subdivided into 16 beat frequency signals with /16 phase difference alternately. The mean square deviation of the output angular rate is reduced and the high resolution signal processing is realized by increasing the counting pulses of MDRLG. Allan variance analysis of experiment results shows that the quantization error is reduced from 0.327 to 0.170 by increasing multiplication. Since the quantization error is the main error source when removing the dither signal of MDRLG, the accuracy of MDRLG is improved effectively by the high resolution signal processing.
Laser-induced plasma by high speed photography
ZHOU Jun, FENG Wei-li, LIU Yong, XU Zhen-hua
2011, 32(5): 1027-1031.
The important parameters and evolution rule of laser plasma can be obtained by diagnosing the laser plasma. Based on the photographs of plasma sparks shot by industrial high-speed CCD under different laser energy levels, the shape, size, color and variation characteristics of plasma were studied. The results showed that plasma plume looked like a liquid-droplet in space and expanded in the opposite direction of the laser beam. With the increase of laser energy, the size of plasma increased greatly in horizontal and vertical directions, and the expand rate slowed down.
Dependence of InGaN-based white LEDs spectral characteristics on junction temperature
CHEN Chao, XIA Ming-fei, YANG Hong-ru, ZHAN Chun-lian, LU Fei, LI Zheng-qi, LV Chun-li, WU Lei
2011, 32(5): 1032-1036.
Junction temperatures and spectral characteristics of InGaN+YAG white LEDs were measured at various driving currents and a constant environmental temperature, and the spectral curve under different junction temperatures was obtained, which indicated the dependence of InGaN+YAG white LEDs spectral characteristics on junction temperature. The experiment results show that the line width of blue spectrum is dependent on junction temperature, while the one of phosphor spectrum exhibits a weak dependence; the peak wavelengths of blue and phosphor spectrum have no dependence on junction temperature, while the peak intensity ratio of phosphor to blue spectrum has a good linearity.
Polarized laser backscattering of atmospheric clouds distribution
ZHAO Ji-zhi, JIANG Yue-song, LU Xiao-mei, YE Ji-hai
2011, 32(5): 1037-1043.
This paper presented a method of using backscatter vertical cross-section and depolarization ratio to analyze the backscatter data of polarization LIDAR of cloud aerosol lidar and infrared pathfinder satellite observations (CALIPSO) satellite. Taking the CALIPSO data on Nov. 23rd and 24th, 2008 for example, it studied the distribution of the cloud in atmosphere in the visible and infrared light in Beijing area. Backscatter vertical profiles and depolarization ratio were drawn by interactive data language (IDL). The vertical distribution directly described the distribution of each component in the atmosphere such as aerosols, low cloud and cirrus, and showed the height of atmospheric boundary layer. The depolarization ratio gave the height and thickness of cloud. Two observations showed that there existed clouds with the thickness of 2 km~2.5 km and the depolarization ratio of 0.2 at the altitude of 3 km~7 km, and the method could distinguish between cloud and aerosol and provide spatial distribution of them more conveniently.
Numerical calculation of transfer coupling equation of externalresonator Raman laser with 579 nm
GUO Jia-xi, LU Bao-le, ZHANG Ren-jian, HUI Dan, ZHANG Hao-lei, REN Zhao-yu, BAI Jin-tao
2011, 32(5): 1044-1048.
In order to increase output power and conversion efficiency of the external resonator Raman laser with KGd(WO4)2 crystal, the radiation transfer equations of the laser system were solved numerically with the method of area summation. The output intensity variation of the first order to the third order Stokes with time and the relaxation oscillation of the Raman laser were obtained. It was found that increasing the reflectivity of the output coupling mirror on the Raman cavity could increase the intracavity intensity of the first order Stokes, which made the energy conversion from the pump laser to the second order Stokes laser easier.
Dynamic characteristic analysis of high-g accelerometersbased on Hopkinson bar
WANG Hua-jun, WANG Yan, LI Xin-e
2011, 32(5): 1049-1052.
Based on Hopkinson bar laser interference shock test-beds, this paper analyzed the dynamic characteristics of high-g acceleration sensors, discussed the concept and feasibility to achieve the amplitude-frequency characteristics of a high-g accelerometer. This method adopted Hopkinson bar as the shock acceleration generator, applied a laser-grating interferometer to obtain the time history of the input acceleration with high accuracy, and processed the waveform combining with the output of accelerometer to obtain the dynamic calibration results. The dynamic calibration result of 988 piezoelectric sensors was given.