2014 Vol. 43, No. 3

Laser and optoelectronic technology application
Characteristics of laser-induced bubbles in different surrounding pressures
Wang Xiaoyu, Wang Jiang'an, Zong Siguang, Liu Tao, Li Shengyong, Liang Shanyong
2014, 43(3): 671-675.
[Abstract](391) [PDF 1724KB](148)
The experimental system for research on laser-induced bubbles in different surrounding pressures was built. Bubbles were produced by pulsed laser focusing into water. A hydrophone was used to receive the acoustic signals produced by laser-induced bubble collapse. The pressure inside the tank was accurately controlled by an air pump. Characteristics of laser-induced bubbles and peak pressure of acoustic signals produced by laser-induced bubble collapse in different surrounding pressures were investigated through simulation and experiment. The results show that the movement period and maximum radius of laser-induced bubbles decrease as the surrounding pressure increases from 0.1 MPa to 0.7 MPa gradually. The peak pressure of acoustic signals produced by laser-induced bubble collapse increases as surrounding pressure increases between 0.1-0.4 MPa, and that decreases as surrounding pressure increases between 0.4-0.7MPa, the change speed of the former is larger than that of the latter.
Damage threshold research of monocrystalline silicon solar cells under femtosecond laser illumination
Tian Xiuqin, Xiao Si, Tao Shaohua, Yuan Zhanzhong, Zhou Yanqiang
2014, 43(3): 676-680.
[Abstract](372) [PDF 1259KB](189)
Femtosecond laser with ultrashort pulse (35 fs) was first applied to investigate damage threshold of a monocrystalline silicon solar cell. Compared with a continuous-wave laser of the same central wavelength, a femtosecond laser pulse was found to have a slightly higher damage threshold. Unlike nanosecond or picosecond lasers, the femtosecond laser has heating pulse time equal to or shorter than the electron- phonon coupling time. Thus, the thermal non-equilibrium effect becomes obvious, and the heat conduction phenomenon no longer meets the law of Fourier. In the damage threshold experiments, a beam shaping technique was applied for a femtosecond laser to generate uniform intensity distribution, which could prevent experimental deviation caused by great concentrated intensity distribution of a conventional laser pulse with the Gaussian profile.
Numerical simulation on attenuation of stress wave in copper target irradiated by intense laser
Zhang Xingquan, Zuo Lisheng, Yu Xiaoliu, Qi Xiaoli, Huang Zhilai, Wang Biao, Duan Shiwei
2014, 43(3): 681-686.
[Abstract](368) [PDF 1674KB](129)
The code Abaqus/Explicit was employed to simulate on propagation of stress wave in a copper foil target, which was induced by intense laser with ns level width. A model was developed to simulate one dimensional planar stress wave propagation and attenuation, and its simulated model consisted of two kinds of elements: finite elements and infinite elements. Fine finite elements were used in laser shocked zone, and coarse infinite elements were used in surrounding zone as no reflecting boundaries. The strain rate effects and ultrahigh pressure effects on material yield stress were also considered. Series of simulations were performed using two different peak values, 0.35 GPa and 3.5 GPa, which were exerted on the target surface by shock wave. The two-step stress wave profile was obtained in copper target under the pressure of 3.5 GPa. The numerical results suggest that shock velocity is 4 600 m/s under the pressure of 0.35 GPa, and 4 000 m/s under the pressure of 3.5 GPa. The value of peak stress attenuates with the propagated distance in form of an exponential function. Some numerical results are in good agreement with the experimental results.
High-frequency analysis on THz RCS of complex conductive targets in free space
Hua Houqiang, Jiang Yuesong, Su Lin, Wen Donghai, Yu Rong, Wu Xiaofang
2014, 43(3): 687-693.
[Abstract](313) [PDF 2182KB](132)
The high-frequency method for the prediction of radar cross section (RCS) of complex conductive targets in the terahertz (THz) band in free space was presented. In order to consider the scattering fields of the complex perfectly electric conducting (PEC) targets in free space, the Green's function was introduced into the conventional physical optics method. Combining the graphical electromagnetic computing (GRECO) method and using the partition display algorithm to improve, the shadow regions were eliminated by displaying lists technology of OpenGL to rebuild the complex targets, and the geometry information was attained by reading the color and depth of each pixel. The THz RCS of complex conductive targets can be exactly calculated in free space. The RCS comparison between GRECO prediction and simulation of FEKO software proves the validity and accuracy of the proposed method. The results provides an important basis and method for the application of THz radar in many fields such as military, astronomy and remote sensing in the future.
Optimization analysis of telescope aperture and truncation factor of coherent LIDAR
Bu Zhichao, Guo Pan, Chen Siying, Zhang Yinchao, Chen He, Chen Shengzhe, Ge Xianying
2014, 43(3): 694-699.
[Abstract](354) [PDF 1851KB](122)
Based on coherent Doppler LIDAR heterodyne detection theory, the heterodyne efficiency analytical expression under both free-space and fiber-coupled detect mode of the coaxial system were unified through the parameter substitution. Combined this formula with the signal-to-noise ratio under turbulent environment, the optimum values of the aperture and the truncation factor under different detection range were obtained for ground based and spaceborne system. The results show that the signal- to-noise ratio of the ground based LIDAR is relatively steep as the telescope aperture changes, the optimum truncation factor is 80% during the whole detect range, and if the aperture selected is not appropriate, it will cause losses of signal-to-noise huge in the system; For Spaceborne LIDAR the signal- to-noise ratio is first increased and then stable as the telescope aperture increased, the optimum telescope aperture can be balanced between the cost and signal-to-noise, and the optimum truncation factor is also 80%. The research has important theoretical significance and practical value both for the development of detection theory and optimal configuration of the coherent Doppler LIDAR.
Design and experiment of a laser ranging scheme for aerospace applications
Yang Ran, Zhang Gaofei, Zhang Zichen, You Zheng
2014, 43(3): 700-706.
[Abstract](369) [PDF 2486KB](166)
In response to the requirements of wide measurement range, high accuracy, real-time measurement to laser ranging system in aerospace applications, a laser ranging scheme was designed by using dispersed direct phase ranging method. The theoretical measurement range can reach 10 km and the degree of ranging accuracy is within 0.1 m. The laser system, narrow-band filter and the APD photodiode were particularly required by analyzing the space background noise (including space radiation, earth radiation and solar radiation) and range equation for non-cooperative space targets. The experimental results indicate that the maximum ranging error of the system is 8.71 cm, and the system has high dynamic performance with the ranging time less than 1 ms. Moreover, the power consumption and quality of the prototype is small(13.29W and 693 g respectively), which makes the system a suitable payload for space- based applications.
Laser spot welding of LF6 aluminum with double laser beams
Ma Yinan, Tao Wang, Chen Yanbin
2014, 43(3): 707-711.
[Abstract](368) [PDF 4881KB](187)
Experiment of laser spot welding of LF6 aluminum with double laser beams was carried. The cross-section of laser spot welding joints with single laser beam and double laser beams were compared, and the effects of laser power, pulse duration and power ratio on the weld joint dimension were investigated. The experimental results indicate that when the power is fixed, the double laser beams can increase the keyhole diameter and improve the stability of the keyhole, decreasing the number of pores, increasing the dimension of fusion area. It is discovered that the dimension of top sheet's change is small, when the laser power changes. And the area of weld joint in the bottom sheet is smaller than that in the top sheet when the laser power is low. At the same total input power, the crater depth with the laser power ratio 1:1 is much smaller than that of laser power ratio 1.5:1.
Picosecond mid-infrared parametric generator based on periodically poled stoichiometric LiTaO3
Zou Yue, Bi Guojiang, Pang Qingsheng, Mao Xiaojie, Wang Jianjun
2014, 43(3): 712-715.
[Abstract](459) [PDF 1140KB](212)
Mid-infrared laser at 3-5 m has very important application in opto-electrionic countermeasure. If the infrared laser is pico-second pulse, as it has much higher peak-power, it will be much more powerful in contermeasure filed. In this paper, tunable optical parametric generator (OPG) pumped by a 1.06 m picosecond laser based on periodically poled stoichiometric lithium tantalate (PPSLT) was reported to get pico-second mid-infrared laser. The periodically poled Lithium niobate crystal was a single structure (29.5 m). The pumping source was a home-made pico-second laser, which used a LD side- pumped regenerative amplifier. The maximum output power was 2.02 W at a frequency of 1 kHz, and pulse-wide was 13.6 ps. A continuous tunable middle-infrared (mid-IR) spectrum (idler wave) of 3.98- 3.68 m was obtained by changing the crystal temperature from 40 ℃ to 200 ℃. When the maximum available average pump power was 2.02 W, the idler output power of OPG was 190 mW at 120 ℃, the optical-optical efficiency was 9.4%. This experimental research shows the possibility to get a output of picosecond mid-infrared laser by OPG at several watts level.
Infrared technology and application
Calibration of common temperature blackbody based on thermal-infrared standard radiometer
Xu Jun, Meng Binghuan, Zhai Wenchao, Ding Lei, Zheng Xiaobing
2014, 43(3): 716-721.
[Abstract](404) [PDF 1813KB](241)
Radiance uncertainties of common temperature blackbodies determine the detection accuracy of infrared optoelectronic dectetor systems. To improve the on-site calibration accuracy of blackbodies'radiance, a standard radiometer was used to calibrate three blackbodies, including one cavity blackbody and two surface blackbodies. The standard radiometer was traced to a standard blackbody hold by National Institute of Metrology of China and obtain a uncertainty of less than 0.22%. Brightness temperatures and effective emissivities were acquired by measuring three blackbodies'radiance directly. The results show deviations of 0.6 K to 2.6 K between brightness temperatures and setting temperatures for all three blackbodies, which correspond to absolute radiance uncertainties from 1.4% to 5.5%. The direct calibration method based on standard radiometer avoids the uncertainties from measurements of temperature and emssivity, and can be used to realize on-site system-level calibrations of blackbodies and absolute radiance monitoring.
Flip chip bonding technology for IR detectors
Geng Hongyan, Zhou Zhou, Song Guofeng, Xu Yun
2014, 43(3): 722-726.
[Abstract](624) [PDF 1188KB](329)
Two-color and four-color detectors have been emerged as the development of Infrared Focal Plane Array technology. Millions of pixels have arisen on the chips and the spot pitch is even less than 13 micron. So high I/O density makes the fabrication more critical. This is beyond the ability of traditional micro-interconnection technology such as wire bonding (WB) technology and tape automated bonding (TAB) technology. Flip chip hybridization offers numbers of advantages over the widely used wire bonding technique such as small package size, high interconnect density and low cost. It consists of procedures: Under Bump Metallization deposition, indium deposition, reflowing, flip-chip bonding and inserting the underfill. Development of every procedure was performed. And the indium bumps were also emphasized for that indium bumping was a critical technology in the application of high-density interconnection between a focal plane array and a Si read-out integrated circuit (ROIC) by flip chip bonding.
IR radiation imaging test, process and evaluation of jet aeroengine
Chen Shiguo, Jiang Yong, Fang Haobai, Li Zu
2014, 43(3): 727-731.
[Abstract](374) [PDF 1645KB](165)
The infrared(IR) signature is the important basis for IR stealth design and anti-stealth detection of jet aero-engine. There were three major contributions in this paper. Firstly, the jet aero-engine had a wide temperature span to be measured, which was far too large for an IR camera to cover in one snapshot. This was accomplished by using multi-integral time combined measure method, each integral time was optimized to a definite range of temperature and to make sure that the combination of all integral times seamlessly covered the entire temperature range of target. Secondly, the measured temperature range of each integral time was defined by multi-frame image time-averaging method, then a per-pixel radiance replacement and images synthesization method was proposed to form an integrated IR image. Compared with IR image of single integral time, the integrated image shows abundant target details and signature information. Finally, the distribution of IR radiant intensity was calculated, compared with IR spectroradiometer measurement at the same test-point, and error was less than 10%. The result shows that proposed methods based on IR camera are all reasonable and efficient.
Modeling of global infrared background based on remote sensing inversion
Yang Fan, Xuan Yimin, Han Yuge
2014, 43(3): 732-736.
[Abstract](422) [PDF 2169KB](134)
The precondition for modeling the earth's infrared background is to derive reliable global surface temperature. The accurate surface temperature could be retrieved based on the data of remote sensing. Choosing the widely used split-window algorithm, the global distribution of the surface temperature was retrieved. Besides, the model of the earth infrared radiance was completely proposed, considering the atmospheric infrared radiance and the atmospheric transmittance in different modes of region, latitude and season. Through a combination of remote sensing technology and infrared radiation modeling technology, the global infrared background radiance was finally calculated and mapped in any band. It can be indicated that, the simulated images are detailed and accurate, and reflected the real infrared characteristics of the earth background. The results have an important application value in thermal environment analysis of space objects, research of space infrared detection and stealth technology.
Calculation and analysis of contrast for satellite-borne infrared detector
Tian Changhui, Cai Ming, Yang Baiyu, Fan Qi, Wang Binke, Wang Weiyu, Qu Shaobo
2014, 43(3): 737-741.
[Abstract](305) [PDF 1388KB](204)
The irradiance contrast formula of target and background for satellite-borne infrared detector under both ground and atmosphere background was derived. The absolute contrast and the relative contrast at various target altitude and temperature were calculated. The analysis conclusions show that the absolute contrast and the relative contrast increase with the target temperature and altitude for wavelength of larger than 2.5 m. The higher the target altitude is, the less the contrast changes per unit distance. The effect of the sun should be considered when the wavelength is less than 2.5 m. For target at 0 km altitude, 2.9-4.1 m is the optimum detective waveband. As the target altitude increases, the available detective waveband broadens and the peak wavelength moves to short wave direction slightly. When the target altitude is higher than 10 km, relative contrast peak value appears at 2.6-2.8 m. The nearer the target is from the ground, the higher the atmospheric attenuation is to infrared radiation.
Technologies of performance improvement for platinum silicide infrared focal plane array
Kang Bingxin, Cai Yi, Wang Lingxue, Xue Wei, Gao Yue
2014, 43(3): 742-748.
[Abstract](400) [PDF 1797KB](147)
Platinum silicide infrared focal plane array is characterized by several advantages such as wide spectral range, large array, good uniformity, high time stability and low cost. It shows application potential in multispectral/wide-spectrum imaging, laser detection, astronomical observation and medical monitor. However, 100mK's sensitivity(NETD) is the main limitation on wide application. The technologies of improving performance of platinum silicide infrared detector were summarized. Optical cavity structure, PtSi/porous Si schottky barrier, doping-spike P+ and suitable PtSi film thickness were effective measures to increase quantum efficiency. Porous silicon structure improved quantum efficiency as much as 27% at 4 m wavelength. Comparing with interline transfer CCD, the fill factor of the FPAs was raised up to 50%-80% using charge sweep device, meander channel CCD or hybrid schottky structure. In addition, microlens array was the most efficient method to augment the fill factor higher than 85%.
Infrared target simulator's polarizing beamsplitter system based on digital-micromirror device
Sun Yongxue, Long Funian, Meng Qingyu, Zhao Xiao, Wang Chao, Zhou Jun
2014, 43(3): 749-753.
[Abstract](387) [PDF 1161KB](161)
Digital-micromirror device has became the most popular device to create infrared image, because of its characteristics as high frame frequency, high spatial and temperature resolution and wide dynamic range. In order to avoid the occlusion and collision between the illumination system and the projection system in the infrared target simulator, a beam splitter prism need to be added, while the ordinary beam splitter prisms have the disadvantage of low light utilization. To solve this problem and improve the light energy efficiency of infrared target simulator, a new splitting method was given based on polarizing principle from physical optics basic theories, and a polarizing prism was designed. Light energy utilization was improved greatly, and satisfactory results were obtained.
A method to determine the domain of a rocket exhaust plume
Liu Zunyang, Sun Xiaoquan, Shao Li, Wang Yafu
2014, 43(3): 754-761.
[Abstract](293) [PDF 2140KB](178)
Aimed at calculating the infrared radiation of a rocket exhaust plume exactly and efficiently, a method for defining the domain of an exhaust plume was reported. As a basic work, the flow field was calculated by using the CFD software FLUENT, and the radiation was calculated by means of Finite Volume Method (FVM). Then, variables that might be able to be used to differentiate an exhaust plume from surrounding atmosphere such as temperature and species composition were studied and the mass fraction of CO was chosen. When calculating the infrared radiation of an exhaust plume, only the part where the CO mass fraction bigger than the threshold was taken into account, and the rest were neglected. The change law of size of calculation domain, calculation time and infrared radiation with thresholds were studied. The results show that, as the threshold decreases, the size of calculation domain and the calculation time increase monotonously and rapidly, while the infrared radiation changes a lot at first and becomes stable at last. Besides, it was indicated by simulation experiments that the CO mass fraction 0.000 5 as the threshold is acceptable to define the calculation domain of the exhaust plume.
Design of CMOS circuit for long wave infrared photoconductive detector
Yuan Honghui, Chen Yongping
2014, 43(3): 762-765.
[Abstract](347) [PDF 1851KB](165)
To design low-temperature CMOS circuit for low impedance infrared photoconductive detector and realizing high performance IR imaging, the use of differential amplifier with symmetrical positive and negative power is necessary. Thus, a kind of two grade CMOS circuit was designed. The first grade was adopted bridge circuit input, this structure was fit for low impedance detector. The positive magnifying method was introduced in second grade. The feedback resistance was designed 1 M, the circuit was supplied by 1.5 V and this circuit was attached to detector without capacitance. The testing results show that the amplifier can work well when it connects with low-impedance infrared photoconductive detector at the low temperature. The circuit total gain exceeds 10 000 times, the 3 dB bandwidth is more than 4 kHz, and the equivalent input noise is less than 1.5 V. The research has perfectly solved the matching problem between high impedance CMOS circuit and low impedance detector.
Stripe nonuniformity correction algorithm based on steering kernel fitting for single infrared images
Zhao Ming, An Bowen, Lin Changqing, Sun Shengli
2014, 43(3): 766-771.
[Abstract](267) [PDF 3548KB](154)
In order to correct the stripe nonuniformity for infrared images captured by infrared linear arrays and uncooled staring infrared focal plane arrays, a novel stripe nonuniformity correction algorithm based on steering kernel for single infrared image was proposed. Firstly, the principal directions and window sizes of steering kernels were determined by the gradient characteristics of infrared images. Then, the estimations of each column pixel were treated as expectations in least square fitting, which was in the constraint of vertical stripe models. The correction parameters in the iteration were obtained, and the image corrected was accepted with a certain probability. The iteration of nonuniformity correction should not be ended until the error function is below the threshold preset. Experimental results indicate that the proposed algorithm has stable and fast convergence. Compared with other three algorithms, the proposed algorithm has the advantage of reducing the stripe nonuniformity and preserving much more edge information.
Information quantity evaluation of thermal imaging systems based on nature background
Wang Jihui, Wang Xiaowei, Chen Songlin, Jin Weiqi
2014, 43(3): 772-778.
[Abstract](290) [PDF 2134KB](140)
In order to research the impact of nature environment on the synthesized performance of thermal imaging systems, a nature background noise factor was presented and introduced into MRTD-CW model comparing with Target Task Performance (TTP) model. An information quantity model based on MRTD-CW model with the nature background factor was proposed to evaluate the impact of nature environment on the synthesized performance of thermal imaging systems. The algorithm of the nature background noise factor was defined by experiments and the normalized form of the information quantity model with the nature noise factor was given. Taking typical scenes as examples, the impact of nature background noise on the synthesized performance of thermal imaging systems was analyzed by the information quantity model with nature background noise factor, and which was consistent with those of TTP model. Results show that the information quantity model with nature background noise factor can analyze the impact of nature background complexity on the synthesized performance of thermal imaging systems and can be applied to the evaluation of thermal imaging systems.
Setup of blackbody's temperature and area for simulating real target
Wang Yanbin, Wang Min, Zou Qianjin, Li Hua, Huang Chenggong, Qi Fengjie
2014, 43(3): 779-784.
[Abstract](315) [PDF 1601KB](199)
The temperature and area of blackbody were researched for simulating the real target in the experiments of infrared countermeasure. First of all, the two principles that should be observed were proposed to effectively simulate infrared radiation characteristic of real object: equality of irradiance and solid angle. The formula which calculates the temperature of blackbody was secondly deduced based on the infrared theories. At last, Jian-7 plane was taken as real target; its infrared radiation characteristic was computed in the different viewing angle, the influence of atmospheric transmittance and path radiation luminance were also taken into account. The temperature and area of blackbody were studied in different viewing angle and distance of the seeker and target. The results show that the variable trend of blackbody's temperature agrees with that of target's radiation luminance and the variable trend of blackbody's area agrees with that of target's projected area under the two principles. The research fruit can provide theoretical basis and data reference for carrying out the countermeasure experiment of infrared guided weapon.
Photoelectrical device and materials
Application of tracking differentiator in semi-strapdown seeker
Sun Gao, Zhu Mingchao, Liu Hui, Jia Hongguang
2014, 43(3): 785-789.
[Abstract](369) [PDF 2340KB](137)
The research of semi-strapdown seeker was carried out, the control principle of semi-strapdown seeker was showed and the integrated stabilization loop of semi-strapdown seeker was proposed. The theory of tracking differentiator was introduced and the simulation was carried out. The simulation study result shows excellent track and filter capability of tracking differentiator. In order to cut down the noise of velocity measurement in semi-strapdown seeker, the tracking differentiator was used. The simulation and hardware in loop result show that the velocity of platform frame is well estimated by tracking differentiator, the stabilization precision of semi-strapdown seeker improves 80% , which testifies the feasibility and validity of the tracking differentiator in semi-strapdown seeker.
Compensation for FOG temperature drift based on adaptive neuro-fuzzy inference
Zhao Xijing, Liu Guangbin, Wang Lixin, He Zhikun, Zhao Han
2014, 43(3): 790-794.
[Abstract](415) [PDF 1678KB](125)
The temperature drift is one of main factors influencing on the precision of a fiber optic gyroscope (FOG). The characteristic of FOG temperature drift was analyzed through temperature experiments. The zero bias temperature drift was compensated using the polynomial fitting method. To deal with the problem of poor compensation precision caused by the fact that the traditional surface fitting method can not describe the relationship between the scale factor temperature drift and the temperature or the angular rate accurately, a novel compensation approach for FOG temperature drift was proposed based on the adaptive neuro-fuzzy inference method. Based on the fuzzy logic, the approach combines the least square method with the back-propagation hybrid optimization algorithm to design an adaptive neuro-fuzzy inference system, so the compensation precision was improved effectively. The experiment results show that the training error root mean square and the predicted error root mean square of the new compensation approach are less than 0.003()/s and 0.005()/s respectively in the temperature range from -30℃ to -60℃ and the angular rate range from -165()/s to 165()/s
Microstructure and property of laser cladding TiC reinforced composition coating
Yang Guang, Wang Xiangming, Wang Wei, Qin Lanyun, Bian Hongyou
2014, 43(3): 795-799.
[Abstract](457) [PDF 3101KB](156)
Based on the optimum component design,wear resistant Ti-matrix functional gradient materials composite coating was fabricated on substrate of a titanium alloy TC4 by laser cladding process using TC4, Cr2C3 and Ti powder blends in order to enhance the tribological properties of TC4. Microstructure of the coating was characterized and the coating microhardness was tested. And its wear resistance was evaluated under room-temperature dry-sliding wear test conditions. The results show that the composite coating has fine microstructure consisting of in-situ TiC particles uniformly distributed in the matrix in the form of big dendrite and graininess structure along cladding direction and is metallurgically bonded to the titanium substrate. The coatings exhibit excellent wear resistance due to the rapidly solidified fine microstructure and the presence of a large amount of in-situ TiC.
Simulation of electric field modulated by silicon-microstructure during non-adiabatic near-field optical etching process
Sun Xiaoyan, Shen Zhengxiang, Tong Guangde, Zhang Jinlong, Wang Zhanshan
2014, 43(3): 800-805.
[Abstract](391) [PDF 1621KB](147)
How to reduce the micro-defects of supersmooth optical surface is one of the research hotspots of manufacturing technology of ultra-precision optical element. A kind of novel precision optical fabrication method called non-adiabatic near-field optical induced smoothing surface microstructure was introduced to remove the surface scratches and digs after conventional polishing process. After establishing the geometry models of microstructures on supersmooth surfaces of silicon, the electric field excited by microstructure under the irradiation of 532 nm laser was numerical simulated by finite difference time domain (FDTD). From the comparison of the maximum intensity of the electric field excited by the microstructure with different sizes, it can be seen that the maximum of local electric field intensity approximately increase linearly with the scale of the microstructure increase. It also shows an increasing trend with gradient of microstructure increase while the peak value is less than 25.5 nm. The physics map of the smoothing of microstructure on silicon surface is described by the numerical simulation of electric field modulated by microstructure under laser irradiation, which gives a way to explain the non-adiabatic near-field optical etching process.
Retardance characteristics analysis of lens in polarization remote sensors
Qiu Zhenwei, Hong Jin
2014, 43(3): 806-811.
[Abstract](521) [PDF 1656KB](115)
The polarimetric accuracy of existent polarization remote sensors is largely controlled by the polarization properties of those instruments themselves. The retardance of lens in the polarization remote sensors is a key part of the polarization characteristics whose stabilities are crucial for finally reliable polarimetric results. By analyzing the effect of the retardance of the lens in the polarimetric remote sensing measurement, it can show that the total retardance equals to the simple summing of each retardance from various optical interfaces with optical coatings, and the main part of total retardance is from optical coatings. The mathematical expression of retardance from single interface's broadband antireflection coatings is derived from thin film theoretical analysis. Typical examples of visible and near- infrared, infrared, ultra-broadband antireflection coatings in actual applications were studied with this expression, the result shows that retardance of general broadband antireflection coatings is monotone decreasing while wavelength increases. Furthermore, the lens in broadband polarization remote sensors can hardly achieve lower overall retardance by compensation between optical interfaces.
Study on 1×11 Dammann grating with sub-wavelength structure
Leng Yanbing, Dong Lianhe, Sun Yanjun
2014, 43(3): 812-817.
[Abstract](484) [PDF 1465KB](204)
In this paper, a high-diffraction efficiency Dammann grating with sub-wavelength structure was designed and prepared based on the Rigorous Coupled-Wave Analysis (RCWA) theory and optimized by the genetic algorithm. The array number of diffractive spots was 11 and the minimum feature size achieved 0.95 m. The design value of diffraction efficiency can achieves 95%, around 15% more than conventional Dammann grating while the uniformity can be less than 2%. By using Electron Beam Direct Writing and Reactive Ion Etching, the sub-wavelength structure was patterned on the silica basement. The experimental results show that the sub-wavelength structure with nanometer resolution can be patterned by electron beam scanning exposure. In reactive ion etching, the etching rate and the grating line-shape can be affected by radio frequency (RF) power, system pressure and gas flow, and the line-width error in Electron Beam Direct Writing was also analyzed.
Polarization properties of one-dimensional photonic crystal doped anisotropic material based on Berreman matrix
Lu Liping, Wei Liangshu, Luo Xiaosen, Ni Xiaowu, Lu Jian
2014, 43(3): 828-832.
[Abstract](376) [PDF 1762KB](163)
In order to study the band gap characteristics of photonic crystal doped anisotropic material, an (AB)10F(BA)10 symmetrically structured one-dimensional photonic crystal was designed and its transmission coefficient was numerical calculated by Berreman transmission matrix. It is found that the two defect modes in the 700-1 000 nm photonic band gap exhibits red shift and their transmission coefficient changes periodically with the increase of thickness of the defect layer F. When changing the azimuthal angle of the uniaxial crystal in F, the defect mode generated by X polarized light moves toward long-wavelength direction and its transmission coefficient changes regularly. But the one generated by Y polarized light has no change. When increasing the during 0-90, a new defect mode appears. These properties of defect modes are of significance in application of filter design.
Optoelectronic devices and materials
Modeling of ion migration depth in field-assisted ion-migration
Wang Guoqiang, Hao Yinlei, Li Yubo, Yang Jianyi, Jiang Xiaoqing, Zhou Qiang, Wang Minghua
2014, 43(3): 818-822.
[Abstract](284) [PDF 1544KB](122)
A model for calculation of time dependence of ion migration depth in glass substrate in the process of field-assisted ion-migration (FAIM) was presented, in which glass wafer temperature rise induced by Joule heating effect was taken into consideration. In this model, glass wafer temperature rise behavior was firstly obtained by solving its thermal balance equation; after that, time dependence of electric current density, and in turn charge flux density flowing through glass wafer was calculated; finally, ion migration depth was calculated by utilizing its universally linear dependence on charge flux density. It can be observed that there exists a reasonable agreement between simulated data and experimental results in the respect of ion migration depth, for experimental conditions conventionally applied for glass-based integrated optical device fabrication. Analysis shows that this model possess wider adaptability than the conventional model in the respect of ion migration depth calculation, due to its involving of glass wafer temperature rise effect induced by Joule heating.
Design of triple-cladding photonic crystal fiber with near-zero flattened dispersion
Song Zhaoyuan, Huang Jinhua, Zhang Leilei
2014, 43(3): 823-827.
[Abstract](343) [PDF 1356KB](140)
In order to obtain the near-zero flattened dispersion at the wavelengths of 0.80 m and 1.55 m, at which the Ti: Sapphire femtosecond laser working wavelength and the optical communication window center, respectively, for the photon crystal fiber (PCF), we used the structural design of a triple-cladding PCF with the hexangular air-hole loop arrangement instead of the general mono-cladding one. Using the improved effective refraction index method on this triple-cladding PCF to perform the numerical simulation, we achieved satisfying results. The numerical simulation shows that the dispersion of this type of PCF changes apparently with small variations of the structural parameters, and therefore the structural designing, that leads to a near-zero(the dispersion range of 0.5 ps/(kmnm) and flattened (the dispersion slope range of 0.02 ps/(kmnm2) dispersion property at the wavelength ranges of 0.80 0.02 m and 1.550.15 m, respectively, is actualized through adjusting reasonably the PCF structural parameters. This result may play an important role on studying the optical communication system and femtosecond laser transmission characteristics in the PCFs to extend its applications.
Modulation of medium refractive index on filter performance of photonic crystal quantum well
Pan Jihuan, Su An, Meng Chengju
2014, 43(3): 833-837.
[Abstract](361) [PDF 1140KB](123)
To design high-quality optical filter device, the modulation of medium refractive indexes in barrier and well layer on filter bandwidth of optical quantum well was studied with transfer matrix theory and computational simulation method. The results show that the filter bandwidth is responsive to the refractive indexes of both barrier layer and well layer; filter bandwidth narrows down as the refractive index of high-refractive medium in barrier layer increased; and the greater ratio between refractive index sums of barrier layer and well layer, the narrower filter bandwidth of optical crystal quantum well becomes. The response mechanism of optical crystal quantum well filter bandwidth to medium refractive index can provide theoretical basis to improve the quality and performance of optical filter device and also has positive effects on the theoretical study of optical quantum well.
Advanced optics
Image motion compensation of off-axis two-line camera based on earth ellipsoid
Wu Xingxing, Liu Jinguo, Kong Dezhu, Zhang Liping, Long Kehui
2014, 43(3): 838-844.
[Abstract](291) [PDF 1409KB](117)
As view axis and optical axis of reflective off-axis two-line stereo mapping camera are separate and the earth is in fact an ellipsoid, distances between objects on earth corresponding to view axis and optical axis vary with geocentric angle from substellar to ascend point. In addition imaging sensor is perpendicular to optical axis while imaging the objects on earth corresponding to view axis. All these factors lead to change of image motion speeds and drift angles along with off-axis angles. Equivalent simplified model of reflective off-axis space camera was established based on analysis of its imaging principle. Formulas of image motion speeds and drift angles of reflective off-axis two-line stereo mapping camera based on earth ellipsoid were deduced. Influence of adjusting row transfer periods and drift angles uniformly on imaging quality of a reflective off-axis two-line stereo mapping camera was analyzed. Results of analysis indicates that if no more than 5% drop of modulation transfer function is used as a constraint, row transfer periods of nadir-view camera and backward-view camera should be adjusted individually as TDI stages is greater than 4. When drift angles are adjusted uniformly, mean value of drift angles of nadir-view camera and backward-view camera should be used and TDI stages should not exceed 89.
Layout of thin catadioptric system and mounting impact analysis of its metal primary mirror
Long Bo, Xing Tingwen, Liao Sheng, Huang Zhiqiang
2014, 43(3): 845-850.
[Abstract](292) [PDF 3218KB](107)
The thin catadioptric system included a metal high-order aspherical primary mirror having an 80 mm aperture, and the distance between the optical vertex of primary mirror and the image interface was only 17.5 mm. To assure the layout of all components successfully and meanwhile thicken the mirror body effectively to enhance the stiffness, the primary mirror with 3 mounting ears was designed, and measures of components combination and crisscross mounting frontward in the same circumferential ring were implemented. Moreover, to evaluate the surface figure of metal mirror under mounting stress,bolt pretension was simulated by using the pretension element in ANSYS, and on the basis of modal check, primary mirror models including flexural supporting structure of different thickness were built and wavefront deformation at mounting state was analyzed. Meanwhile, the instance of flatness diversity of mounting interfaces was considered. The schemes of mirror assembly structure with restricted axial distance, the integrated analysis way of mounting stress simulation on wavefront deformation, and measures to decrease the distortion provide the reference on the optomechanical design to increase the mirror surface accuracy after assembling thus assuring the system image quality.
A novel compact large relative aperture visible optical system
Wang Hu, Luo Jianjun
2014, 43(3): 851-855.
[Abstract](368) [PDF 1236KB](170)
Based on the special chromatic aberration and thermal aberration of diffractive optical element, which are used in optical system of visible camera for space debris, a novel compact and good image quality large relative aperture space debris camera optical system was designed. The novel system solved the problem that the conventional system had small relative aperture and complex structure. The novel system had an effective focal length of 100 mm, a relative aperture of F/1.5, a field of view of 6. The system met the requirements of visible space debris camera in encirc energy, the dispersion spot diameter, lateral color, distortion, athermalization and so on. This novel system had light weight, compact structure and good image quality by using diffractive optical element, which provided a new idea for designing visible space debris camera optical system.
Simulation study of rotating double optical wedge vectoring optics path based on Matlab
Guo Yunzeng, Yang Xiaojun, Jia Haini, Wang Haitao, Liu Feng, Jiang Zhi
2014, 43(3): 856-860.
[Abstract](464) [PDF 1914KB](282)
The optical wedge plays a guiding and key role on the processing of high-precision micro-hole drilling by laser pulses. In order to improve the laser micro-hole processing quality, a method was presented to improve the analysis on the impact of the optical wedge on accuracy of laser micro- manufacturing. First the concept of the equivalent of a single wedge vector was proposed. The double wedge vector model was established and analyzed based on the definition of a single wedge vector, and the new method of the vector superposition of the multiple wedges was came up with. Secondly, the simulation software was programmed by using Matlab. The simulation results show the trail of the laser pulses through the double optical wedge. The effect of the quality of the micro-hole caused by the un- synchronization of the motion system is investigated. The deviation quantitative analysis is carried and the formula of calculation the deviation is given. The conclusion is of great value to the performance indicators of designing the controlling system in the high-precision micro-hole drilling by laser pulses.
Design of space optical system with double infrared waveband based on image space scanning
Li Gang, Fan Xuewu, Zou Gangyi, Wang Hongjuan
2014, 43(3): 861-866.
[Abstract](337) [PDF 1907KB](175)
The design of optical systems with wide ground coverage are restricted by the size of infrared detector. This problem can be solved by choosing the appropriate imaging mode. A kind of image space scanning method was given in the paper. It could satisfy the optical systems with general area infrared detectors. The picture was built by image mosaics technology. Because the image space scanning method needs to be done in the parallel light path, the design method of three-mirror afocal system was studied based on two-mirror afocal system and the formulas to compute the initial structure was given. The optical system consists of afocal system, scanning mirror and imaging part. The scanning mirror was placed at the exit pupil of the afoacl system. The MWIR and LWIR were separated by the field-bias method and imaged respectively. The simulation analysis shows that the Narcissus is under control and the MTF of the optical system is very close to the diffraction limit.
Optical design for an LED traffic signal light
Liu Xiaodong, Li Xiangning, Sun Hui
2014, 43(3): 867-870.
[Abstract](277) [PDF 1713KB](166)
An LED traffic signal light without obvious granular sensation was designed, which had a uniform distribution of luminous intensity in a certain angle range. The emergent rays of the highlighted LED were collimated by a Fresnel lens. A pillow lens was designed and arrayed to achieve the specified direction lighting and a uniform distribution of luminous intensity in a certain angle range by using the Snell's Law. The design was simulated by using the optical design software ZEMAX and the results that the luminous intensity was distributed uniformly were given in both horizontal and vertical angles. The design was proved to meet the design requirement by simulating the imaging of signal light in human eyes and showing the observing effect of eyes. The applications of the design in practical engineering were analyzed in the article.
Current progress in head-mounted display based on retinal scanning
Hu Xinrong, Liu Ying, Wang Jian, Li Chun, Sun Qiang, Li Jing, Liu Bing
2014, 43(3): 871-878.
[Abstract](415) [PDF 2005KB](771)
Recent years, along with the development of head mounted display (HMD) in lightweight and miniaturization, a new style of HMD which is based on retinal scanning is gradually becoming a research hotspot in both fields of virtual reality and helmet mounted display. With a unique scanning device to control the coherent beam generated by the laser diode (LD) and scan the beam in two dimensions to produce an image, retinal scanning display (RSD) can directly scan an image on the observer's retina, which has the advantages of large field of view, high brightness and compact structure. Based on the RSD's research reports and results of foreign countries, the basic principle and technological developments of RSD were briefly summarized. Meanwhile, the current progress and key technology in this field were emphasized. At last, a brief outlook about the future development trends and application prospect of RSD was discussed.
Design of a novel eyepiece for low-level-light night-vision system
Shen Mande, Jiang Qingxiu, Ren Huanhuan, Li Fei, Li Cheng
2014, 43(3): 879-883.
[Abstract](538) [PDF 1219KB](162)
To resolve the contradictions between high performance, low distortion and lightweight ,a novel eyepiece with freeform surface and diffractive surface was presented. Based on the conventional erfle eyepiece, a noel eyepiece with freeform surface and diffractive surface was designed by Zemax software. The noel eyepiece system consisted of three lenses. Only glass K9 was used in the noel eyepiece system. The optical performance of the noel eyepiece were compared with the erfle eyepiece. It is shown that the novel eyepiece not only has better performanc, as transverse aberration, lateral color, distortion and field curvature, but also has greatly improved in weight and total length, which can meet the demands of night vision eyepiece system. It also provide a new approach for lightweight and compact low-level-light night- vision eyepiece system system designs.
Photoelectric measurement
Research of atmospheric transfer correction in radiance measurement:atmospheric radiative transfer model and the analysis of key atmospheric parameters
Wei Heli, Dai Congming
2014, 43(3): 884-890.
[Abstract](291) [PDF 1765KB](209)
The signal of a target measured by electro-optics detector is attenuated by the atmosphere and affected by atmospheric background radiance. Atmospheric transfer correction is important to the measurement of target's radiation characteristic. The commonly-used atmospheric radiative transfer models and the detecting methods of important atmospheric optics parameters affecting atmospheric radiative transfer were introduced. The atmospheric parameters affecting infrared radiative transfer were analyzed, the analyzed results indict those key atmospheric optics parameters must be measured in the atmospheric transfer correction system.
In-pipe surface circular structured light 3D vision inspection system
Wang Ying, Zhang Rui
2014, 43(3): 891-896.
[Abstract](403) [PDF 3132KB](186)
The in-pipe surface defect inspection is very important for pipe maintenance and repair. An pipe inner surface 3D vision inspection system was proposed based on the vision principle by using circular laser projector. Firstly, the principle of the circular laser light vision was given, and the in-pipe 3D vision inspection system based on the axial pattern was proposed aiming to the restricted space of the inner pipe. According to the characteristics of the inner pipe inspection system the planar target was designed with which the calibration of this system was completed. Finally, the industrial pipe's inner surfaces were inspected based on the proposed circular structured light system, and the 3D shapes of in- pipe surfaces were reconstructed. Experimental results indicate that the system's calibration precision is 0.081 mm and the measurement system proposed in the paper is suitable for the industrial pipe inner surface inspection.
Concentration inversion algorithm in ammonia slip monitoring in situ based on laser technology in high temperature
He Ying, Zhang Yujun, Wang Liming, You Kun, Gao Yanwei
2014, 43(3): 897-901.
[Abstract](330) [PDF 1253KB](239)
Accurately, sensitively and rapidly monitoring of ammonia slip after the flue gas denitration to avoid ammonia secondary pollution of the environment is one of the focuses in industrial and environmental fields. This research chose the absorption line of ammonia molecules near 1.53 m as the goal line, studied the ammonia slip in situ monitoring method of high temperature flue gas through TDLAS technology and wavelength fast scanning technology, and designed the corresponding open-path measurement system. This research analyzed the temperature influence on measurement in the high temperature environment, studied the temperature correction method, designed an ammonia concentration accurate inversion algorithm which avoided calibration in flue-site and obtained the maximum relative detection error which is 1.5% by laboratory experiments. The engineering practicability and reliability of the algorithm of the system is proved by industrial field installation and operation. It will provide the effective technical support in industrial denitration process monitoring and the flue gas emissions in safety in our country.
Calibration and analysis of line-scan camera based on virtual stereo pattern
Wang Zichen, Dai Ming, Li Gang, Wang Yongyang, Song Yueming, Gao Yujun
2014, 43(3): 902-907.
[Abstract](331) [PDF 1380KB](150)
A novel method that can be used for improving line-scan camera calibration according to its features was proposed. Firstly, the designed planar pattern and multiple exposures of line-scan camera were used to produce a virtual stereo calibration pattern. Secondly, a mathematical model was analyzed and established to seize the relation between the coordinates of calibration points on the pattern and those of their images. Then, the technique of least mean square and iterative optimization were employed to solve both the over-determined equations for multiple feature pointsand nonlinear parameters of lens. The impact to the calibration result that was caused by the non-parallel nature between the camera and calibration pattern was also analyzed. Finally, both the analysis and experimental results reveal that this proposed calibration method is not only convenient and flexible, but the calibration points are also independent of calibration pattern and that the condition of parallelism is not required. All these features make the devised method accurate and practical.
Design of telescope servo system based on DSP and FPGA
Deng Yongting, Li Hongwen, Wang Jianli, Yin Yumei, Wu Qinglin
2014, 43(3): 908-914.
[Abstract](454) [PDF 1877KB](279)
A digital controller based on digital signal processor (DSP) and field programmable gate array (FPGA) was designed to solve the problem of high precision and low velocity of large telescope ac servo system drove by permanent magnet synchronous motor (PMSM). A DSP was used as primary controller to perform the function such as computing control algorithm and receiving instructions. A FPGA was used as secondary controller to achieve the function such as PWM generation, current sampling and speed acquisition. Mathematic model of PMSM was found based on vector control, and hardware of PMSM digital controller was designed. The large telescope table was tested at low speed through employing adaptive PI controller after completing the controller hardware design. The experiment results demonstrate that when the large telescope table run at 32.4 ()/s, the range of velocity fluctuation is 0.648 ()/s; when the large telescope run in the mode of sine guide, which is with the maximum velocity 1 ()/s and maximum acceleration 1 ()/s2. The maximum guide error is 9.72 , and the value of RMS error is 3.24. The drive control system can realize high precision control of large telescope and meet the need of system performance.
Laser ranging precision in sending and receiving coaxial optical system in indoor instance
Gao Po, Hu Yihua, Zhao Nanxiang, Wang Yong
2014, 43(3): 915-919.
[Abstract](271) [PDF 1502KB](193)
The precision of pulse laser ranging is the key factor of two-dimensional laser scanning imaging. It is very important to develop pulse laser ranging technology of sending and receiving coaxial optical system in indoor instance to improve the capability of two-dimensional laser scanning imaging. Relationship between the precision of pulse laser ranging and the laser echo energy was analyzed by simulation. The basic design scheme of optical system of the two-dimensional scanning imaging were proposed. In indoor instance, the nonlinear relationship between the laser echo energy and range of sending and receiving coaxial optical system was calculated and the nonlinear curve between the laser echo energy and range was delineated. Finally, the nonlinear relationship was verified by the actual test data and the effect of the nonlinear relationship on the precision of pulse laser ranging was analyzed. The study of thesis has important value in the design of system of laser ranging and the conclusion can be applied to perfect the design of optical system of pulse laser ranging in indoor instance.
Optical communication and optical sensing
Temperature control system for SLD optical source of FOCS
Cao Hui, Yang Yifeng, Liu Shangbo, Xu Jintao, Zhao Wei
2014, 43(3): 920-926.
[Abstract](560) [PDF 1554KB](174)
To lower the influence of optical source temperature property on the precision of fiber optic current sensor(FOCS) in high voltage grid, an analog temperature control system was proposed to control the optical source working temperature. According to the designed goal, design process of each key section was introduced. A proper temperature signal bridge was analyzed which could obtain a linear relationship between the output differential voltage and temperature. The mathematical model of the system was established in the frequency domain; the transfer function of the system was calculated; and the parameters of proportional-integral-derivative (PID) controller were analyzed in the time domain. A temperature controller used for FOCS super luminescent diode (SLD) optical source was designed, which was verified by fixed temperature test and temperature cycle test. The results show that by means of the real time temperature control, the accuracy of FOCS is up to 0.2 level which reaches industry requirements.
Long wave infrared transmission in atmospheric channel
Cong Rijin, Wang Jingyuan, Xu Zhiyong, Wang Rong, Wang Zhe
2014, 43(3): 927-932.
[Abstract](447) [PDF 1484KB](164)
A free space optical communication channel model including stochastic transfer distance and direction of photon after being scattered was developed using a Monte Carlo simulation method based on photon tracing. In this model, beam divergence and field of view(FOV) were introduced, the influence of scattering was also in consideration. Simulations using Monte Carlo method and Lambert-Beer Law were carried out under fog condition with long wave infrared. Compared with Lambert-Beer Law, the result shows that the received energy of scattering can't be ignored under the condition of short range and low visibility. The influence of different ranges, visibilities, beam divergences and field of views on pass loss were analysed respectively using Monte Carlo method. The contributions of different scattering orders to total received energy were also illustrated. The effects caused by the 4th or higher orders scattering can be overlooked under given conditions so as to improve the efficiency of calculation.
Experimental research on vibration influence and compensation of space light to fiber coupling efficiency
Han Qiqi, Wang Qiang, Ma Jing, Tan Liying
2014, 43(3): 933-939.
[Abstract](442) [PDF 1725KB](150)
Utilizing the existing mature technologies of fiber-optic communication is an important development direction of the present satellite optical communication technology, but the critical issue of how to couple the space light into the fiber must be resolved. A theoretical analysis of the influence caused by the vibration of satellites on the coupling efficiency of space light into fiber was conducted. On this basis, using CCD as a detector and fine steering mirror as a compensation facility, a vibration compensation system of satellite optical communication terminal was established and an experimental study was conducted. The experimental results show that the active compensation system based on the feedback control technology suppresses low frequency vibration efficiently. When the vibration frequency ranges from 1 to 50 Hz and the vibration amplitude ranges from 75 to 300 rad, the maximum improving of coupling efficiency brought by the compensation system is up to 54.73% . The results verify the feasibility and effectiveness of the compensation system established in this paper, and lay a foundation for the using of the various fiber components in the satellite optical communication system.
Advanced optical imaging technology
Study of Cs content on UV-visible rejection ratio of Cs2Te photocathode
Liu Hui, Zhang Liandong, Feng Liu, Cheng Hongchang, Gao Xiang, Miao Zhuang
2014, 43(3): 940-943.
[Abstract](473) [PDF 1159KB](160)
UV-visible rejection ratio is an important parameter for determining SNR of all-day ultraviolet detector system. In order to study the effect of Cs sensitization on UV-visible rejection ratio S280 nm/S320 nm of Cs2Te ultraviolet photocathode during the activation, many activation experiments by using three different groups of Cs content were carried out. Respective comparing the results of UV-visible rejection ratio and the spectral response curves of 200-400 nm, the rejection ratio values of Cs2Te photocathodes activated with different Cs content varied from 4.0 to 7.6. As Cs content grew, the integral sensitivity of photocathodes increased correspondingly between 260 nm and 320 nm, while the growth of the radiation sensitivity at the peak of 256 nm was not remarkable. So this paper focused on the influence of Cs content on the spectral response whose wavelength was more than 320 nm.
Leaf area index retrieval from remotely sensed hyperspectral data
Li Ziyang, Qian Yonggang, Shen Qingfeng, Wang Ning, Liu Yaokai, Ma Lingling, Kong Xiangsheng
2014, 43(3): 944-949.
[Abstract](332) [PDF 2377KB](157)
An experimental leaf area index (LAI) retrieval model was proposed with the aid of a leaf- radiative transfer model (PROSPECT) and a canopy bidirectional reflectance model (SAILH) to simulate the canopy reflectance in this paper. Then, the vegetation indices (VIs) were introduced, and the sensitivities were analyzed between LAI and VIs, soil background. Based on the sensitivity analysis, a modified chlorophyll ratio index II (MCARI2) was proposed by Haboudane et al. (2004) was used to build the LAI retrieval model, because it is rather sensitive to the LAI and insensitive to soil background. Finally, the retrieval model proposed was performed to estimate LAI from the hyperspectral data. Compared with the ground-measured LAI, the LAI retrieved from hyperspectral data underestimate approximately 0.42.
Optical design of spectrally tunable source for hyperspectral calibration
Zhai Wenchao, Xu Jun, Zheng Xiaobing, Ding Lei, Lu Junhua
2014, 43(3): 950-955.
[Abstract](274) [PDF 1724KB](148)
The fine structures of traditional calibration sources and target spectra may have differences, which could hinder the calibration accuracy of hyperspectral remote sensors. Furthermore, traditional sources are difficult to be measured accurately. To solve such problems, a novel spectrally tunable source based on digital micromirror device (DMD) and spectroradiometer structure was introduced. The optical system of the new source was designed. The principles of the system, structural parameter calculation of the system and the process of optical design were described in detail. The results indicate that the optical system's performances are near-diffractive-limit in the whole band from 0.4 m to 1.0m. The RMS spot radii are less than 3.5 m and the MTFs at 37 lp/mm are near 0.8 for all the design wavelengths, which meet the requirements of the source.The novel source is promising to improve the imitation accuracy of target spectra, and it could also be measured accurately by detector-based calibration method. With these features, the new source is helpful to reduce the calibration uncertainties of remote sensors.
Application of calibration-free wavelength-modulation spectroscopy in measurements of gas temperature and concentration
Pan Hu, Wang Guangyu, Song Junling, Yu Xiaohong
2014, 43(3): 956-960.
[Abstract](321) [PDF 1291KB](242)
Tunable diode laser absorption spectroscopy is widely used in many applications,with difficulty of abstracting baseline,it is hard to be used in high-pressure and high-disturbing conditions. It's indicated in theory of wavelength-modulation spectroscopy that the first and second order harmonic signals contain tow common terms: incident intensity and gain of detector. By normalizing 2f signal with 1f signal (2f/1f), dependency of 2f/1f signal on incident intensity was eliminated, absolute strength of a spectra can be obtained subsequently. With measured laser parameter and known spectral parameters, theoretical 2f/1f signal was simulated by numerical calculation. Calibration-free wavelength-modulation spectroscopy was built based on frequency demultiplexing method, by numeric lock-in code. When a temperature stabilized cell was set at 600 K, 700 K, 800 K, precision of 2% is achieved compared with thermocouple measurement, which indicates that the method is much more reliable and adaptable.
Information processing
Fusion of infrared and visible images based on NSUDCT
Yang Yang, Dai Ming, Zhou Luoyu
2014, 43(3): 961-966.
[Abstract](260) [PDF 2576KB](138)
Aiming at the infrared and visible images in a same scene, a novel fusion algorithm based on the nonsubsampled uniform discrete curvelet transform (NSUDCT) was proposed. First, the source images were segmented using the marker controlled watershed segmentation (MCWS), and the joint region graph was obtained by superimposing the segmented results. Then, the nonsubsampled uniform discrete Curvelet transform was applied to the source images, the low-frequency coefficients were fused with the measurement of ratio of region contrast and region standard deviation, the high-frequency directional coefficients were fused with the local energy fusion rule, and the consistency of the fused coefficients was examined. Finally, the fused image was reconstructed from the subband fused coefficients. The experiment results indicate that the proposed method could provide better fusion quality in terms of both visual and quantified measure. Compared with the pixel fusion method based on NSUDCT, the Entropy of fused images increased by 9.87% , the Cross Entropy decreased by 68.04% and the Mutual Information increased by 80%.
Infrared moving object detection under the condition of rotating scan
Li Lin, Lu Huanzhang, Xiao Shanzhu, Liao Bin
2014, 43(3): 967-972.
[Abstract](284) [PDF 2454KB](119)
Aiming at the problems of infrared moving object detection under the condition of rotating scan system, several methods were presented, and an optimal solution was selected. Firstly, according to the characteristics of infrared image, a projection matching method was used for the image registration. Aiming at the faults of traditional moving object detection methods, combining the advantage of frame difference and the classic self-adaptive background difference algorithm, a new approach was presented based on differentiated self-adaptive background difference algorithm, which made the pseudo moving object decreased obviously. At last, learning from the image registration, a method based on the least subtraction of mean gray value was proposed to remove the pseudo moving object effectively. Experimental results show that the presented algorithms can resolve the problems brought by the rotating scan mode quickly and effectively.
Best slant-plane estimation based stereo matching algorithm
Cao Xiaoqian, Ma Caiwen
2014, 43(3): 973-978.
[Abstract](303) [PDF 2213KB](226)
A novel stereo matching algorithm based on best slant-plane estimation was proposed in this paper in the purpose of eliminating stair-casing which showed up frequently in the slant scene matching process where the window-based matching algorithm was used. In this procedure, a slant parameter vector was randomly attributed to every pixel in the reference image firstly, then, those vectors were iteratively propagated between neighbor pixels followed by a recursively slant-plane parameter refinement process for each pixels in the principle of whether a lower cost could be got under the new slant-plane parameter vectors, until the parameter vectors were converged to the best slant-plane parameter vectors while a sub-pixel disparity was got for each pixel in the reference image. Experiment results indicate the effectiveness of the algorithm, the performance of the algorithm on the slant scene is ranked on top of those state-of-art algorithm which is relatively close to the algorithm proposed here, while the performance on the normal scene is comparable with the state-of-art algorithm.
Minimum error thresholding for infrared image under constraint of cross entropy
Liu Songlin, Niu Zhaodong, Chen Zengping
2014, 43(3): 979-984.
[Abstract](412) [PDF 1905KB](138)
Focusing on the infrared images which have similar statistical distributions between object and background, conventional thresholding methods only take variance or entropy by someway as criterions for thresholding selection and they don't consider actual characteristics of infrared images, so the segmentation results are unsatisfactory. In order to solve this problem, a novel method of cross entropy constrained minimum error thresholding of infrared image was proposed. Firstly, cross entropy was called to measure the similarity between object and background's statistical distributions. The smaller the cross entropy was, the more similar the distributions were. After that, classification error was minimized when the cross entropy was below a certain value. Constraint of cross entropy guaranteed the segmentation process fits actual characteristics of images. Meanwhile, minimum of classification error ensured the effectiveness of segmentation results. The principles of proposed method are clear and the parameter setting is simple. Experimental results on real images show that compared with several classic thresholding methods, the proposed method can improve thresholding segmentation accuracy of infrared image with similar statistical distributions between object and background effectively.
Optimized design of automatic panoramic images mosaic
Yang Lei, Cao Jianzhong, Tang Linao, Gao Bo, Wang Hua, Guo Huinan
2014, 43(3): 985-990.
[Abstract](479) [PDF 4848KB](218)
An optimized algorithm of automatic panoramic image mosaic was presented based on time and frequency domains. Firstly, the improved phase correlation method was used to sort the panoramic image sequence automatically and then determine the overlap region. In order to reduce the false match rate of the corner, the brightness of the overall image was adjusted automatically according to the overlap region's pixel mean. Then, an improved Harris operator was adopted to extract corners (with no need to set threshold value manually), the initial feature points pairs were obtained by the bidirectional greatest correlative coefficient and the false feature point pairs were rejected by RANSAC algorithm. Finally, the nonlinear smoothing algorithm was adopted to fuse the overlap regions of the image. The experimental results show that optimization algorithm is simple and effective in the sorting process. Compared with the existing algorithm, the optimization algorithm proposed at present makes a great progress in the success rate and the efficiency in the matching and extracting process of feature points. The stitched image is with great clarity, soundness and stitching accuracy.
Preprocessing of infrared star map and position accuracy analysis of star point
Wei Wei, Liu Enhai
2014, 43(3): 991-996.
[Abstract](419) [PDF 2123KB](150)
As the raw data of daytime star gazing, there are single-point-noise, stripe noise and some other noise in infrared star map, which severely affect the sequential star-point extraction and centroid localization. According to the star map of field star gazing, methods of star map denoising and star-point position accuracy analysis were studied in the paper. An algorithm for single-point-noise detecting and compensating and a colum mean offset correction (CMOC) algorithm for stripe denoising were proposed. Then, a complex filtering method of Wiener 2 and Top-hat was used to denoise the star map furtherly. At last, a method of adding ideal simulated star-point to observation star map was used to calculate the starpoint centroid position accuracy. Experimental results indicate that the preprocessing method could denoise various kinds of noise in infrared star map, and the peak signal-to-noise ratio of star point target could be raised from 4.7 to 31.3, and the standard error of star-point localization of simulated 2 Mv star could achieve 1/30 pixel, which satisfies the accuracy of engineering application.
A simple method for removing accumulative error in subaperture stitching
Feng Xiaoyu, Zong Xiaoying
2014, 43(3): 997-1001.
[Abstract](295) [PDF 3729KB](135)
Subaperture stitching interferometry is an effective means for measuring optical surfaces and systems. But the more subapertures are used, the more serious effect the accumulative error in stitching has on the accuracy. So finding a simple and fast way to remove the accumulative error is the key for improving subaperture stitching. An effective and quick method to eliminate the accumulative error in stitching was proposed in this paper. The plane mirror which was 180 mm 80 mm was tested by six subapertures stitching in the experiment. And the method which was proposed in this paper could get rid of the accumulative error in stitching very well.
A fast test and recognition method for object character
Wang Huanhuan, Yang Qingping, Wang Xiangjun
2014, 43(3): 1002-1008.
[Abstract](281) [PDF 2641KB](146)
A new method of fast test and recognition of moving object was presented in the article, that is suitable for fast inspection and recognition of object with complex texture and moving state in unceasing changing view angle. A new coding method based on Multilevel Orientation Run Length Coding (MORLC) was developed, and the two new templet models with MORLC coordinate and length coding were developed in the research. Systemic theory process and criterion were given in the the article, and experiment data of object character inspection and recognition by MORLC coordinates and length coding and templets were given. The MORLC coding and templets shows benefits with small data anount, small storage addresses, easy constructing, high processing speed, flexible coding form with different multilevels resting with different application situation, high robusticity, low mistakes, etc. The method can be used for fast inspection and recognition of moving objects at moving state in unceasing changing view angle, especially character test and recognition of a great lot products.
Application of cusp catastrophic theory in image segmentation of infrared thermal waving inspection
Wang Dongdong, Zhang Wei, Jin Guofeng, Yang Zhangwei, Tian Gan
2014, 43(3): 1009-1015.
[Abstract](503) [PDF 3765KB](176)
Image segmentation is the key technique to achieve the quantitative identification in the thermal waving inspection. An image segmentation method was advanced based on the cusp catastrophic theory according to the characteristics of discontinuous change between the region with defect and without defect in thermal images. The amplitude and phase of the image were computed at first, then the model of the cusp catastrophic was established and the corresponding transform of coordinate was studied, the variable of the system was dealt with unitarity. The salutatory dots were signed based on the judicative formula of the cusp catastrophic model after the unitariness, the framework of the salutatory dots was picked up to realize the segmentation of the thermal waving images through the operation of the expansion and fill. At last the experiments were carried out to prove the feasibility of this method.