2013 Vol. 42, No. 4

Articles
Effect of composition ununiformity of LPE HgCdTe film on response spectral of device
Cui Baoshuang, Wei Yanfeng, Sun Quanzhi, Yang Jianrong
2013, 42(4): 845-849.
[Abstract](201) [PDF 271KB](172)
The effect of composition ununiformity of LPE HgCdTe film on spectral response of device was studied. A new method was proposed to calculate the spectral response of HgCdTe IR detector. This method considered longitudinal composition distribution and transverse composition ununiformity in LPE HgCdTe film. The coherent and incoherent light transmission among the device was also included. Using this method, the variation law of peak responsibility of spectral responseand and cutoff wavelength with compositional diffusion width z and transverse composition deviation of LPE HgCdTe film was calculated. The result indicates that for common LPE HgCdTe film, whose is less than 0.002, the influence of transverse composition ununiformity on spectral response can be neglected. The changes of peak responsibility and black body responsibility with thickness of LPE HgCdTe film were also calculated. The optimum thickness can be obtained.
Infrared radiation of plume in three typical flow state
Zhu Xijuan, Li Xia, Wang Jun, Liu Xingrun
2013, 42(4): 850-856.
[Abstract](238) [PDF 441KB](150)
The infrared radiation in 3-5 m band of axisymmetric Laval nozzle in underexpanding, designing and overexpanding conditions were simulated by a three-dimensional(3-D) exhaust system infrared radiation code. The 3-D flow field of the jet was simulated numerically by finite volume method(FVM), RNG k- turbulence model, and the infrared(IR) radiation code of the plume was developed by FVM coupled with narrow band model in non-gray absorbing-emitting media. The results indicate that the plume IR radiation intensities of underexpanding state are maximal, those of the designing and overexpanding decrease in turn, which related to flow characteristics, it illuminates that the IR radiation of plume canbe affected by the flow characteristics, that canbe controlled by controlling the flow.
Numerical analysis on the unsteady infrared radiation characteristics of terminal-sensitive submuniton
Liu Lianwei, Yang Miaomiao, Xu Zhenling, Fan Hongjie, Wang Min
2013, 42(4): 857-862.
[Abstract](270) [PDF 460KB](290)
To calculate the transient infrared radiation released from the terminal-sensitive submuniton,a numerical simulation of the unsteady temperature distribution for the terminal-sensitive submuniton performed by using the software Fluent, which taking into account three factors as follows, aerodynamic heating, irradiative heat transfer and structure heat conduction. Then, the infrared radiation characteristics of both submuniton body and parachute were obtained by calculation at 3-5 m and 8-12 m waveband, the changes of infrared radiation for the whole trajectory were also analyzed. Also, this paper calculated the infrared radiation of atmosphere in the gazing direction, which was compared with the infrared radiation of terminal-sensitive submuniton. The results show that the infrared radiance of parachute is a half of the infrared radiance of submuniton body at least, but the infrared radiation intensity of parachute is 21 times of the infrared radiation intensity of submuniton body at most, and it was preferable to take warning of terminal-sensitive submuniton at LWIR and the deceleration and dispinning stage of the trajectory.
Development and calibration of infrared standard radiometer
Xu Jun, Meng Binghuan, Zheng Xiaobing, Zhai Wenchao, Li Jianjun
2013, 42(4): 863-868.
[Abstract](332) [PDF 484KB](178)
Accuracy of blackbodies' reference source radiance is one of the crucial factors that determine the accuracy of infrared sensor's absolute radiometric calibration. To improve the measurement accuracy of blackbodies' radiance, a infrared standard radiometer was developed to calibrate blackbodies' radiance directly. The principle and the opto-mechanical design of the instrument were described in detail, and the radiometer was calibrated against a high accuracy water-bath blackbody. The experimental results demonstrate that radiometer's instability is less than 0.03% with in one hour and the uncertainty is less than 0.22%. This corresponds to a brightness temperature uncertainty of 73 mK at 308 K. The radiometer possesses the advantages of system-level measurement and high-precision tracing standard, and by which the blackbodies' radiance can be traced to the radiant standard in lab.
Preparation and characterization of silica composite aerogels with broadband IR absorption
Han Chaojiang, Ma Yongjun, Pei Chonghua, Zeng Min
2013, 42(4): 869-873.
[Abstract](391) [PDF 576KB](139)
The silicon aerogel substrate was prepared by a two-step base/acid catalyzed sol-gel process using tetraethoxysilane(TEOS) as silicon source and by freeze drying. By adding different content of triethylamine hydrochloride(TEAHCl) to the substrate during the aging process, composite aerogels with broadband absorption in mid-and far-infrared windows was prepared. The structure and property of composity aerogels were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), N2 physisorption at 77 K and Fourier-transform infrared spectroscopy(FT-IR). Results show that the triethylamine hydrochloride is crystallized adhering to the whole three-dimensional network of silicon aerogel. The silicon aerogel substrate has the specific surface area about 524.5 m2/g, total pore volume about 1.2 cm3/g and average pore diameter about 9.2 nm. The composite aerogels have the specific surface area about 37.93-138.7 m2/g, total pore volume about 0.08-0.28 cm3/g and average pore diameter about 7.1-8.8 nm. The apparent density of silicon aerogel substrate and composite aerogels are 0.25 g/cm3 and 0.35-0.51 g/cm3 respectively. The composite aerogels have the characteristic of broadband absorption in mid-and far-infrared windows. The relative absorption intensity in mid-infrared window increased in proportion with the increase of TEAHCl.
Numerical simulation of defects depth quantitative measurement in pulsed infrared nondestructive testing
Li Meihua, Zeng Zhi, Shen Jingling, Zhang Cunlin
2013, 42(4): 875-879.
[Abstract](394) [PDF 568KB](227)
Quantitative measurement of defect depth is an important application of pulsed infrared nondestructive testing. The calculation principle of peak second derivative of the temperature decay curve in the log scale was analyzed based on one-dimensional heat conduction model. The stainless steel sample which has six flat bottom holes with same diameters and various depths at the back surface was used. Ansys was used to simulate the process of pulsed infrared nondestructive testing. The depth of defects were calculated by method PSDT. The results of Ansys and pulsed infrared nondestructive testing were compared and analyzed, which indicate that the Ansys model in accordance with the experiment. This research provides theoretical basis for the quantitative study of infrared nondestructive testing.
Study on the infrared radiation characteristics of UAVS’skin
Xu Dingguo, Sang Jianhua, Luo Mingdong
2013, 42(4): 880-884.
[Abstract](346) [PDF 628KB](259)
In order to study the infrared radiation characteristics of BWB-UAV skin, infrared radiation intensity of typical stealth UAV of the 8-14 m band were calculated by the form of a combination of the flow field calculation commercial software and self-developed infrared computing software using the discrete transfer method. In the IR calculations, the emission and reflection of the solid wall of the engine, aircraft skin launch, gas, CO2, H2O and CO absorption and emission effects were talked into account. The results showed that: the Mach number is one of the impact factors that affecting infrared radiation characteristics on 8-14m band; The cooling, insulation measures that lowering the heat affected zone of the skin temperature fuselage engine or coating the infrared emissivity of materials on the fuselage skin can significantly reduce the infrared radiation characteristics of 8-14 m band. The conclusions provide a useful reference for the future aircraft infrared stealth design.
Design of infrared wide waveband double-layer harmonic diffractive optical system
Sun Ting, Zhang Xuanzhi, Chang Weijun, Li Yuan, Hu Bo, Guo Xiaogang, Yang Huamei, Chen Xiuping
2013, 42(4): 951-954.
[Abstract](259) [PDF 760KB](220)
Diffractive optical element(DOE) and harmonic diffractive optical element(HDOE) have overwhelming superiority on achromatisation and athermalisation over traditional refraction and reflection optical elements due to their unique dispersion and temperature effect, which may improve the performance of the optical system and simplify the system structure. But, the diffraction efficiency of both are dependent upon wavelength, that will reduce the imaging contrast in wide waveband. However, Double-layer HDOE could weak the dependence. So,they were used in this infrared wide waveband system, the materials were Ge and ZnSe respectively, the microstructure thickness of corresponding diffractive surface were 73.3 m and 149.3 m. The diffraction efficiency of the system over whole waveband was larger than 97.5%. The emulational result in Code V indicates that various aberrations in system is satisfactory. Especially, the chromatic aberration of wide waveband(8-14 m) is well corrected, secondary spectrum is controlled preferably, and MTF closes to the limit of diffraction. Finally,the measured result indicate that all performances meet optical system expectation.
Optical design of adaptive front lighting system based on digital micro mirror device
Wu Han, Zhu Xiangbing, Zhu Qian, Chen Chun, Wang Cheng
2013, 42(4): 955-959.
[Abstract](488) [PDF 797KB](132)
The road safety of vehicles in night depends on the street illumination directly. Adaptive Front lighting System(AFS) can automatically provide different illumination modes by adjusting the shape, distance and light distribution of illumination according to the surrounding environment to improve the driving security. Considering the problems that less light efficiency of present AFS, one solution of AFS using Digital Micro mirror Device(DMD) was presented. It consists of lamp, reflector, light pipe, DMD and lens. DMD is the core of this system. And the second light pipe was used to collect the unused light energy. The experimental results show that the light efficiency is improved largely by the using of the second light pipe. And it can achieve different beams easily by accuracy controlling the luminance of every pixel on the screen. Because of its flexibility and higher light efficiency, this scheme is expected to show on market.
Radiometric characteristics simulation of large aperture integrating sphere bosed on LightTools
Liu Hongxing, Ren Jianwei, Li Xiansheng, Wan Zhi, Liu Zexun, Li Baoyong, Sun Jingxu
2013, 42(4): 960-965.
[Abstract](419) [PDF 810KB](354)
In order to develop the large aperture integrating sphere with perfect radiometric characteristics, 15 integrating sphere models with 5 different lamp positions and 3 different illumination models were built and simulated by LightTools, and their irradiance plan uniformity and Lambert characteristic were analyzed. Compared with designing by experience, computer simulation has the advantage of short period, low cost and good repeatability. Simulation results indicate that lamp positions and illumination models have less effect on irradiance plan uniformity, however have more effect on Lambert characteristic. The Lambert characteristic of lamp direction is worse than other directions, symmetrical illumination model improves the Lambert characteristic, and the Lambert characteristic usually becomes better with the distance between the light source and the joint plan of both hemispheres increasing. The irradiance plan uniformity, the Lambert characteristic of light source's direction and the Lambert characteristic of light source's vertical direction of a 3 m integrating sphere were tested, with different illumination models, and the measured performance agreed well with simulation results.
Suppression of stray light in a catadioptric and re-imaging LWIR system
Meng Weihua, Xiang Jiansheng, Ni Guoqiang
2013, 42(4): 966-970.
[Abstract](370) [PDF 814KB](251)
Stray light suppression in a catadioptric and re-imaging LWIR system was discussed. The optical system which comprised a classical R-C reflective optics and a re-imaging refractive optics was designed for a compact and low-cost ⅡR seeker. The source and path of stray light in this system were investigated by simulating the optic-mechanical model with LightTools. According to the simulation, the mechanical light stops were built, and the performance of stray light suppression was analyzed. After assembled, the optical system and its anti-stray light effect were evaluated by testing the angle limit away from the sun. The results of simulation and test indicate that there is no influence of stray light on the LWIR system outside 7 from optical axis.
Preparation of diamond films as an infrared optical material by high power microwave plasma CVD
Yu Shengwang, An Kang, Li Xiaojing, Shen Yanyan, Ning Laiyuan, He Zhiyong, Tang Bin, Tang Weizhong
2013, 42(4): 971-974.
[Abstract](506) [PDF 816KB](275)
Polycrystalline diamond films were prepared by using H2-CH4 as the source gas in a newly developed ellipsoidal cavity type MPCVD reactor. The influence of CH4 concentration on the diamond growth and quality was studied in this paper. On the basis of the above research, large area optical grade free-standing diamond film was prepared. Surface and cross-sectional morphology as well as the quality of the diamond films were examined by scanning electronic microscopy and Raman spectroscopy. Furthermore, the infrared transmittance of the samples was measured by Fourier transform spectrometry. The results show that the growth rate of the diamond films increases with the increase of CH4 concentration. However, when the CH4 concentration is increased to certain level, the diamond growth rate will no longer increase. High quality diamond films can be prepared when the CH4 concentration is between 0.5%-2%. The results prove that high quality optical grade diamond films can be obtained by this newly developed ellipsoidal cavity type MPCVD reactor.
Performance analysis of a kind of moving reflector’s mechanism with small coupling displacement
Xiao Qianjin, Jia Hongguang, Han Xuefeng, Xi Rui
2013, 42(4): 975-981.
[Abstract](228) [PDF 967KB](265)
A kind of moving reflector's mechanism with small coupling displacement was studied to control the reflector's movement of Michelson interferometer in FTIR spectrometer. On the basis of a single and double parallel four-bars mechanisms, the moving reflector's mechanism was created by employing flexure hinges. And the static and dynamic characteristics of the mechanism system driven by piezoelectric ceramic(PZT) actuator were analyzed. The results reveal that there is no coupling displacement produced with the mechanism when force is symmetrical, while the coupling angle of the mechanism is small to 10-6(in degrees) when force is unsymmetrical, and that the maximum stress of the mechanism is about 0.5 times lower than that of double parallel four-bars mechanism at the same output displacement. Moreover, the natural frequency fn of the electromechanical system composed of PZT actuator and the mechanism is 4 times higher than the fundamental frequency f of the mechanism, which meets the requirement of dynamic performance. The study will provide a basis and some valuable theoretical guidance for future research.
Polishing of large-aperture mirror and analysis of power spectral density
Wang Wei, Xu Min, Li Hongyu, Yu Guoyu
2013, 42(4): 982-987.
[Abstract](357) [PDF 888KB](174)
As the development of modern optical technology, especially space optical science, more high precision mirrors with large apertures are needed. But it is difficult to manufacture high precision large aperture optical components of multi-scale processing. The method of optical polishing using an ultra-precise bonnet was based upon the technology of computer controlled optical surfacing. A bonnet filled with air was applied as a precise polishing tool which was flexible and able to adapt itself well to the shape of the part, which was superior than other polishing methods. A material removing model of bonnet processed polishing was established according to kinematic principle based on the Preston equation. The model was modified in terms of Hertz contact theory using the physical characteristics of polishing bonnet tools. A satisfactory result was obtained for one of the surfaces of a wedge mirror with a diameter of 570 mm. The result of P-V and RMS parameters are 1/8 and 1/75 respectively. The PSD curves of the part and the noise of the narrow band are analyzed, as well as the reasons.
Design of primary mirror cover for large aperture telescope
Chen Baogang, Wang Shuai, Yang Fei, Zhang Jingxu
2013, 42(4): 988-992.
[Abstract](307) [PDF 859KB](159)
In order to protect the primary mirror of a meter-class telescope, the petal-type cover was designed. The main structure form of lager aperture telescope which have completed at home and aboard were introduced briefly. On the basis of offset slider-crank mechanism which was evolved from four-bar linkage mechanism, a four bar structure which did not need brace existing was proposed. In addition, the kinematic model was created and the force analysis was carried out. The driving torque of motor, displacement of slider and operation time of cover were calculated. Practical application shows that the cover is reliable and effective to prevent the dust and dropped objects from polluting or damaging the primary mirror. The time to open or close the cover is about 62.5 s. The life of no fault is more than one year using in Changchun area. The operation number of no maintenance are more than 500. So the design satisfies system requirement and provides reference for the coming researchers. 
Application for transfer alignment of FOG SINS based on federated filter
He Xiaofei, Wang Wei, Huang Jixun
2013, 42(4): 993-997.
[Abstract](228) [PDF 837KB](113)
Researched on the moving base transfer alignment of the ship synthesize navigation information system on the shipborne weapons associating integrated navigation information system of the warship, put forward flexure and time delay as system state, and gave system state equation and measurement equation. This paper used federal filter as the information fusion algorithm for transfer alignment program, variable of system equation was analyzed by method of PWCS, the velocity and attitude matching sub-filters equation and major filter equation were deduced. At last, this method was simulated and the result of simulation showed azimuth misalignment used federated filter was better than traditional filter 20 percent; application for federated filter could resolve the problem of transfer alignment for FOG SINS about the ship is effectively.
Facility for calibration of ultraviolet and vacuum ultraviolet spectral irradiance
Chen Yinghang, Sui Zuoning, Sun Hongsheng, Wei Jianqiang, Li jingfeng, Li Shiwei, Sun Guangwei
2013, 42(4): 998-1002.
[Abstract](392) [PDF 822KB](258)
In order to adapt the fast development of ultraviolet detection and fitting the requirements for the calibration of ultraviolet optical sources and ultraviolet detectors, a facility for calibration of ultraviolet and vacuum ultraviolet spectral irradiance was set up. The facility was composed of standard optical source (deuterium lamp), standard detector(intensive silicon diode), ultraviolet monochromator, vacuum chamber and so on. The double standards and compared method were adopted in the facility to calibrate the equipments. As well as the value of the standard detector and source were transferred to the detector and the source which were calibrated. Spectral range is 110-400 nm.The maximum uncertainty for calibrating the detector is 12%(k=2), and for the optical source is 20%(k=2).
Parameter design and test of airborne all-day star sensor
Ren Bingwen, Jin Guang, Wang Tiancong, Zhong Xing, Zhang Peng
2013, 42(4): 1003-1010.
[Abstract](370) [PDF 939KB](210)
In order to provide parameters design method of airborne all-day star sensor, in this paper, the SNR(Signal to Noise Ratio) computation formula for star targets detection was derived according to the SNR formula of optical-electric detection system and sky radiance data from Modtran software. The relation between detection SNR and diameter, F number,exposure time was researched for the stars of visual magnitude of 3.5,4,4.5, and the corresponding parameters design method of airborne all-day star sensor was given. In order to verify the correctness of the design method, the ground-based observation test was carried out. Polaris(Mv2.02) was selected as target, and the all-day star sensor prototype with 83 mm diameter, 1 500 mm focal length was designed. Through the ground-based observation test, at the most powerful sky radiation moment the SNR for detection Polaris was 6.84 dB, met the minimum detection requirements 6 dB from the theoretical calculation. The correctness of the design method is verified.
Back-illuminated 283 nm AlGaN solar-blind ultraviolet p-i-n photodetector
Wang Xiaoyong, Chong Ming, Zhao Degang, Su Yanmei
2013, 42(4): 1011-1014.
[Abstract](370) [PDF 865KB](209)
By an optimized fabricating process, a kind of solar-blind ultraviolet photodetector was designed and fabricated used AlGaN material grown on sapphire substrate by metal organic chemical vapor deposition(MOCVD) method. The external quantum efficiency gets well improved. The structure of the device is back-illuminated p-i-n type. Al mole factor is 40% in both p and i type layers and it is 65% in the n type lawyer. The shape of the device is a circle and its diameter is 500 m. The spectral response of the device starts form 260-310 nm while its peak response occurs at 283 nm. Under zero bias, a dark current density of 2.710-10 Acm-2 and a responsivity of 13 mA/W are found which corresponds to a parameter R0A of 3.8108 cm2 and a detection rate of 1.971012 cmHz1/2W-1. Under -7 V bias, the responsivity reaches to 148 mA/W, corresponding to an external quantum efficiency of 63%.
Acetylene gas concentration on-line monitoring using TDLAS
Ding Zhiqun, Bao Jilong, Zhao Hongxia, Zhang Xueshou
2013, 42(4): 1015-1019.
[Abstract](497) [PDF 895KB](170)
A novel acetylene concentration on-line monitoring system using the tunable diode laser absorption spectroscopy(TDLAS) technology was introduced. Near infrared (NIR)distribute feedback laser diode(DFB LD) was used as light source, 0.5 m short path absorption cell, 16-bit analog-to-digital data-acquisition card obtains four channels data which should be processed by a personal computer, four channels obtain separately by varying the laser wavelength using different temperature and different light paths (signal light path and reference light path). Wavelength modulation spectroscopy(WMS) technique is slowly ramping the wavelength by scaning weak absorption lines of acetylene. Fast Fourier transform (FFT) analysis obtains the harmonic signal of absorption spectrum in the harmonic detection(HD). Because interfered by residual amplitude modulation and the laser small dc drift, some digital signal processing techniques such as mean value, digital filtering and background correction are implemented to improve the signal-to-noise ratio. Both theory analysis and experimental results show that the sensitivity of this system can meet the needs of transformer incipient fault diagnosis, which structure is compact and its calibration and adjustment of lightl path are easy.
Design of a miniature single-grating displacement measuring system with nanometer resolution
Yang Dongxing, Yan Shuhua, Du Liebo, Wang Guochao, Lin Cunbao, Zou Pengfei
2013, 42(4): 1020-1025.
[Abstract](264) [PDF 957KB](246)
As the extensive application of nanotechnology and the deepened cognition of nanometer measurement, the measuring technologies of displacement with nanometer resolution were paid extensively attention to. On the basis of researching in working principle of the reflex-grating measurement, a miniature single-grating displacement measuring system with nanometer resolution was designed as well as realized. The overall design, optical structure, and software algorithm of the system were elaborated. In the end, comparative experiments were done with the help of auxiliary instruments which mainly included a capacitive displacement sensor named ASP-10-ILA. Experimental results show that the system can measure accurately when the two signals are not absolutely orthogonal, and the resolution of the system is 1 nm theoretically; the mean values of the measuring system deviates from the reference values by a maximum of 118 nm, and deviates from the fitting-line by no more than 100 nm when the grating displacement experiments are done within the range of capacitive displacement sensor; the deviations of the results are less than 5 ppm when the grating has displacement larger than 10 mm.
Hybrid dual-cladding photonic crystal fiber with high birefringence
Li Zhiquan, Li Sha, Hao Rui, Li Xiaoyun, Zheng Wenying
2013, 42(4): 1044-1049.
[Abstract](279) [PDF 983KB](150)
In this paper, a kind of hybrid cladding photonic crystal fiber was proposed. The model field distribution, birefringence, confinement loss and chromatic dispersion of fiber fundamental mode were simulated by multipole method. It was found that the newly designed fiber shows relatively higher birefringence and lower confinement loss. Then the birefringence and confinement loss of the hybrid cladding photonic crystal fiber were dominated by cladding air holes in the fiber. Simulation results show that the dispersion and dispersion slope are both negative over C band and L band. The birefringence is higher than 10-2, and the confinement loss is lower than 10-5 dB/m under the condition of =1.0 m,d1=d2=d3=0.8 m at the wavelength of 1.55 m.
Numerical simulation of dual-wavelength-pumped supercontinuum generation in an all-fiber device
Wang Yanbin, Li Hua, Wang Min, Zou Qianjin, Qi Fengjie, Yuan Chun
2013, 42(4): 1050-1055.
[Abstract](413) [PDF 955KB](251)
Dual-wavelength-pumped supercontiuum generation in an all-fiber device has been theoretically investigated. Firstly, a theoretical model of dual-wavelength-pumped experimental scheme in an all-fiber device was given. Secondly, by solving the generalized nonlinear Schrdinger equation with the adaptive split-step Fourier method, formation of dual-wavelength pump source and supercontinuum generation one after another were realized. The simulation results agree with the experimental observations very well and reveal that the conjugate action of soliton self-frequency shift and soliton trapping through cross-phase modulation can effectively extend the spectral range to the visible wave band. The research can provide theoretical supports in the realization and construction of dual-wavelength-pumped supercontinuum all-fiber device.
Radiation-induced loss of pulsed γ-ray on optical fibers
Liu Fuhua, An Yuying, Wang Ping, Chen Shaowu, Xie Honggang, Liu Weiping, Shao Bibo
2013, 42(4): 1056-1062.
[Abstract](381) [PDF 987KB](155)
General mechanisms for effects of -ray radiation on optical fibers were studied. Absorption coefficient of -ray, cross sections of different effects, energy and flux and angle distributions of resulting Compton recoil electrons in optical fibers were calculated. An experimental method for transient radiation-induced loss measurement was presented. In order to measure transient radiation loss induced by pulsed -ray in optical fibers, it was developed that an experimental measurement system which applied analog broad bandwidth optical fiber links with five different wavelength lasers such as 405, 660, 850, 1 310 and 1 550 nm. Two different kinds of pulsed -ray devices with average photon energy of 0.3 MeV, dose rate of 2.03107 Gy/s and average photon energy of 1.0 MeV, dose rate of 5.32109 Gy/s were used to irradiate four types of optical fibers in experiments. The transient radiation-induced loss and its relationship with total doses of exposure were measured, and also the permanent radiation-induced losses with light spectrum, changes of refractive index. The experimental results show that: (1) The transient radiation-induced loss will increase as the detecting laser wavelength shifts from near-infrared to visible regions of optical spectrum.(2) Under the same experimental condition, the transient radiation-induced loss of multimode fibers is slightly larger than single-mode fibers.(3) The radiation of -ray will slightly decrease the refractive index of optical fibers.(4) Within a certain dose range transient radiation-induced loss in multi-mode fiber displays a nearly linear dependence upon total dose. The conclusion can be deduced that the generation of new color centers in fiber materials due to Compton electrons will increase the absorption loss and the changes of refractive index will lead to additional waveguide loss in optical fibers. Both radiation-induced loss mechanisms exist simultaneously; therefore, radiation-induced loss is the result of joint action of the two.
Simulation of optimum algorithms with wavefront sensorless in satellite-to-ground laser communication
Cai Yi, Wang Hongman, Qi Bo
2013, 42(4): 1063-1068.
[Abstract](235) [PDF 922KB](159)
In the system of satellite-to-ground laser communication, the atmosphere disturb reduces the quality of communication. Correcting disturb at the sink of the communication can improve the quality of communication. Sometimes, the sensor can't estimate the wave-front, so it needs to use wave-front sensor-less to correct the disturb. In order to compensate the disturb real-time, we simulated three improved optimum algorithms to correct the disturb, and compared the differences among Genetic algorithm(GA), sealing annealing algorithm(SA) and model-based approach algorithm in the convergence speed, precision, stability and the number of adding voltage to the deformed mirror. The simulation shows that: GA convergences very slowly, but can improve normalized intensity form 0.079 5 up to 0.99, It can be used in correcting the static aberration, the model-based approach algorithm only need two iterations to improve normalized intensity form 0.079 5 up to 0.862, It's proper for correcting the atmosphere disturb real-time.
Performance simulation and analysis of all-optical XOR gate at 40 Gbit/s
Deng Dapeng, Cao Dongdong, Zhu Feng, Huang Kai, Li Jiang
2013, 42(4): 1069-1073.
[Abstract](315) [PDF 954KB](150)
In order to improve the output extinction ratio of all-optical XOR gates based on SOA-MZI structure, and optimize the performance of system, the SOA was combined with the HNLF, and the all-optical XOR simulation experiment model based on SOA-MZI was built on the simulation platform of optical communication system designing software OptiSystem7.0, and the all-optical XOR simulation experiment was carried out to two RZ format data signals at 40 Gbit/s. In addition, the all-optical XOR out signals based on SOA-MZI was optimized by a kind of optimization structure which was designed by using the nonlinear effects of HNLF, and the signal waveform diagram of time domain and eye diagram of system before and after optimizing were analyzed and compared. Through a lot of repeated experiments, the optimal system parameters were obtained to make the extinction ratio of all-optical XOR gate based on SOA-MZI be improved from 10 dB to about 28 dB. The experiment results show that the output extinction ratio of conventional all-optical XOR gate based on SOA-MZI is lower because of the incomplete destructive interference, but this problem is solved perfectly by optimizing, the output extinction ratio is improved, and the system performance is optimized.
Experiment set up for RIM-FDS with single mode illumination
Peng Huan, Zheng Yongchao, Zhong Zhi, Shan Mingguang, Wu Xueying
2013, 42(4): 1074-1078.
[Abstract](283) [PDF 948KB](144)
To overcome the shortcoming of low sensitivity in RIM-FOS with LED illuminating, a theoretical model was introduced and an experiment system was designed using LD coupling with single mode fiber as illumination purpose. The system is made up with LD module, optic module, PIN detection module, signal collection module, FPGA module, up computer system and power module. The validation of model was proved by experiment results and the performance of RIM-FOS was presented. Experimental results indicate a sensitivity of 3.15 mV/m and linear region of 380 m for front slope, a sensitivity of 0.76 mV/m and linear region of 690 m for back slope of RIM-FOS. Good stability and repetition are proved for system, and the system will play a significant effect for the further study of RIM-FOS with single mode illumination.
Improved infrared image neural network non-uniformity correction algorithm
Zhao Chunhui, Liu Zhenlong
2013, 42(4): 1079-1083.
[Abstract](493) [PDF 942KB](170)
The responsive of infrared focal plane arrays(IRFPA) is different; it will affect the quality of imaging system seriously. Non-uniformity correction technology will need in practical application. The calibrated images have the problems of blurring and existing ghost artifacts when use the traditional neural network correction algorithm. And it is bad for the observation of the target. After analysis the reasons for the problems in the traditional neural network correction algorithm,proposed the improved algorithm. Replace the mean filter, which used in the traditional algorithm, by the nonlinear filter. The corrected image by the improved algorithm not only a marked improvement in clarity, but also effectively eliminate the problem of artifacts in traditional algorithms.
Realistic infrared image generation method of target
Huang Xi, Zhang Jianqi, Zhang Shaoze, Wu Xin
2013, 42(4): 1084-1088.
[Abstract](266) [PDF 976KB](254)
To meet the great demand of realistic infrared images of target for simulation experiments, a realistic infrared target image generation method was proposed, which based on the combination of measured data and three-dimensional simulation. The surface radiation distribution of target was measured, which was used as input data to a retrieval model for target temperature distribution. Then the infrared textures of target were created using the retrieved temperature distribution, and mapped to a three-dimensional geometry model. The realistic infrared image was generated by 3D rendering technique. The experiments demonstrate that the generation method is good flexibility, and the infrared images are accurate in infrared feature, rich in texture detail and strong in practicality.
Drogue detection algorithm in visual navigation system for autonomous aerial refueling
Song Chunhua, Gao Shibo, Cheng Yongmei
2013, 42(4): 1089-1094.
[Abstract](391) [PDF 1001KB](290)
Drogue detection is important for relative navigation system for probe-and-drogue autonomous aerial refueling. It is a challenging task to detect the drogue with random motion due to disturbances caused by both the tanker wake vortex and atmospheric turbulence. In this paper, the problem of drogue detection was considered as moving object detection. A method based on multi-scale low rank and sparse decomposition was proposed for drogue detection. Firstly, the image sequences were decomposed by stationary wavelet transform respectively. Then the object in the low frequency sub-band image sequences of coarse scale was used as object confidence map to feedback the low sub-band image sequences of next fine scale for low rank and sparse decomposition. The experimental results show that the proposed algorithm is effective for drogue detection in real autonomous aerial refueling data.
Visible and infrared image fusion based on multi-level method and image contrast improvement
Peng Yiyue, He Weiji, Gu Guohua, Tong Tao
2013, 42(4): 1095-1099.
[Abstract](263) [PDF 984KB](148)
An effective infrared and visible image fusion algorithm was propased. Based on Petrovi? multi-level image fusion system, firstly, it was enriched with the edge components from high-frequency information to get higher image quality. Secondly, a method to enhance the contrast of the fused image which make a further improvement in the image quality by analyzing characteristics and the physical characteristics of the targets in infrared and visible images was given. The subjective observation and comparison of objective indexes prove together that the proposed algorithm does a better job than other comparing methods and the contrast enhancement method can be widely used and improve the visible and infrared fused images' quality obviously.
Research on modeling and rendering of realistic infrared texture of grassland
Liu Qian, Zhu Feng, Hao Yingming, Jin Zenghui, Fu Shuangfei
2013, 42(4): 1100-1105.
[Abstract](231) [PDF 991KB](174)
Texture is one of the most important factors to create visual realism in images. Infrared texture generation plays an important role in the field of infrared imagery simulation, and provides an effective way to satisfy the urgent need of realistic scene simulation. In order to generate realistic infrared texrtures directly in image space, a novel method for modeling and rendering realistic infrared texture of grassland was proposed. It mainly researched modeling the temperature field and the structure mophology of grassland. Firstly, the radiation transfer process in soil-vegetaion-atmosphere system was analyzed, which was expressed in the coupled infrared radiation model. Secondly, the spatial distribution pattern of grassland were simulated. Finally, infrared radiation properties were mapped to image space to generate realistic texture images. The infrared textures of grassland under close or magnification observation state were simulated. Theoretical analysis and simulation results justify the effectiveness and resonableness of the proposed method.
Fast template matching algorithm based on AMSP and initial threshold estimation
Wang Lucai, Yi Xinian, Chen Xiaotian, Liu Xin
2013, 42(4): 1106-1111.
[Abstract](353) [PDF 955KB](193)
The Normalization Cross Correlation(NCC) measure is more stable than Sum of Absolute Differences(SAD) measure when the illumination changes. However, it needs large calculated amount, which is its disadvantage. Therefore, a fast template matching algorithm based on NCC combing Adaptive Multilevel Successive Partitioning (AMSP) with the initial threshold estimation was proposed in this paper. The template image was partitioned into different blocks steeply according to the gradient values of the different modules in the template image, the summation of cross correlation was partitioned into different levels with the partition order to get the upper bounds of each layer, and the Cauchy-Schwartz inequality was used to get the relation between different upper bounds, then the approach of adaptive multilevel successive partitioning elimination was formed. In order to further accelerate the matching speed, the initial threshold estimation was used to generate a large boundary threshold, which could eliminate lots of unmatched points as initial searching and reduce the number of search points. The experimental results demonstrate that the proposed algorithm has strong robustness, and the execution speed of the proposed approach is superior to traditional algorithms.
Laser and optoelectronic technology application
Modulation-free frequency stabilization system of external cavity diode laser based on Sagnac loop
Wei Fang, Sun Yanguang, Chen Dijun, Fang Zujie, Cai Haiwen, Qu Ronghui
2013, 42(4): 885-889.
[Abstract](264) [PDF 615KB](157)
A novel frequency stabilization method of ECDL using a phase difference biased Sagnac loop was proposed. This scheme uses polarization beam splitter (PBS) for input and output of Sagnac loop instead of the beam splitter, and a quarter waveplate to introduce a bias phase difference of /2 between the counterpropagating pump and probe beams with perpendicular polarization. A polarizer is inserted after the output of the Sagnac loop, so that the dispersion phase shift induced by Rb resonance can be obtained. By this method, an error signal with larger amplitude can be acquired, which provides an ideal error signal to stabilize the frequency of the laser. Compared with the previously proposed method, whose bias phase difference is introduced by polarization dependent phase shift in total-internal-reflection(sin=0.64), the amplification factors of dispersive signal sin can be achieved to theoretical maximum. This scheme is simple, robust, and has potential applications in atomic physics experiment and so on.
Experiment of large field laser active detection system
Shi Guang, Zhang Haiyang, Geng Zhongbo, Yang Suhui, Zhao Changming
2013, 42(4): 890-894.
[Abstract](314) [PDF 632KB](200)
In order to meet the need of the remote rapid search for enemy snipers on the battlefield, the maximum detection distance model based on the theory of cat eye effect was improved. The MATLAB software was used to generate the curves related to laser power, CCD sensitivity, and maximum detection distance. An active laser detection system which was capable to identify the cat eye target in large field of view and long distance quickly was built. The experiment result shows that the prototype system can realize identifying snipers with active laser detection in the distance of 1 200 m. A feature recognition algorithm for images captured under complex background was put forward, which greatly improved the visibility of the captured images in the experiment. Automatic feature recognition based on the cat eye target was realized. The research is very important to enhance and improve the effectiveness of the laser active detection system on the battlefield.
Optimization design on angle parameters of single-beam pulsed laser orientation recognition underwater system
Zha Bingting, Zhang He, Zhang Xiangjin, Xu Jing
2013, 42(4): 895-899.
[Abstract](489) [PDF 665KB](152)
Aiming at the necessity of fuze getting distance and azimuth information of the target in the short range(greater than 10 m) when underwater target warhead interaction, in order to take full advantage of transmission laser energy, increase the laser echo power, did optimization design on angle parameters of single-beam pulsed laser orientation recognition underwater system. The echo power equation of underwater target detected by pulsed laser orientation recognition system was derived, the relationship between the echo power and the angle parameters was built, the angle conditions and the expression of perfusion area's distance were got. Based on the multi-island genetic algorithm, the angle parameters were calculated by iSIGHT software. The results show that when the angle between the emitting beam center and the axis is 30, the angle between the receiving field of view center and the axis is 34.5, and the field angle take 10 can obtain the minimum perfusion area's distance in the case without consider other factors. Thus, this work can provide a theoretical basis for designing the angle parameters of single-beam pulsed laser orientation recognition underwater system.
Preliminary study on evaluation criterion to laser precision guided weapon by jamming
Zhang Wenpan, Liu Yanfang, Yin Ruiguang, Zhao Hongpeng, Wang Ya
2013, 42(4): 900-903.
[Abstract](252) [PDF 642KB](173)
A method of evaluation criterion was required to evaluate the jamming effects at laser precision guided weapon by hitpoints. The hitpoints of laser precision guided weapon was acquired from photoelectric hardware-in-the-loop simulation tests. With probability theory and mathematical statistics, the method of evaluation criterion was built. The distribution principle of a laser guided bomb was proved by Kolmogorov-Smirnov test, and an evaluation criterion to evaluate the angle deception jamming effects at a laser guided bomb was made by the method. The evaluation criterion was used to evaluate jamming effects of an angle deception equipment to the laser guided bomb. The method of evaluation criterion, which was a preliminary studies on evaluation criterion, was proved proper by the evaluation.
Error analysis and correction for hardware-in-the-loop simulation system of laser guidance weapon
Fan Shipeng, Lin Defu, Wang Jinran, Wang Wei
2013, 42(4): 904-908.
[Abstract](306) [PDF 697KB](163)
According to the characteristic of laser guided weapon, a hardware-in-the-loop simulation (HILS) model for guidance and control system was founded. Then, all kinds of errors impacting on simulation system, especially geometric error, were analyzed, and a guidance model with error was created. Through the mathematic simulation, the maximal angle error was given to limit miss distance within allowable range. In order to correct the geometric error, a model of HILS was developed for seeker to track a certain laser spot on curtain. Using the obtained results, nonlinear over determined equations of error parameters were established. With combination of Newton iteration method and weighted least square method, the error parameters were solved and geometric model was corrected accurately. The results indicate that this approach has achieved exceptional accuracy and reliability, which is significant for next phase of HILS.
Hydrostatic delay correction for satellite laser altimeter
Ma Yue, Li Song, Weng Yinkan, Zhou Hui
2013, 42(4): 909-914.
[Abstract](270) [PDF 722KB](154)
The laser pulse transmitted by satellite laser altimeter bends for atmospheric refraction and extends the ray paths, and it is necessary to correct the atmospheric delay to get accurate ranging results. The hydrostatic delay is the major component of total zenith delay, which is only decided by surface pressure. The hydrostatic equation of static atmosphere was deduced under the condition of non-ideal gas, and surface pressure model was established relevant to geopotential height. Combined with the meteorological data of NCEP and position and elevation data of GLAS, the surface pressure was calculated by numerical integration of 4 order Runge-Kutta algorithm, and then the hydrostatic delay was obtained. Through the respective comparisons between the hydrostatic delays got by this method and the NCEP estimated surface pressure with the GLAS official results, the trend and accuracy of this method are both better with the maximum error less than 2 cm. It is concluded that the hydrostatic delay of satellite laser altimeter can be corrected effectively and accurately by the method based on hydrostatic equation and numerical integration.
Laser aerosol-scatter signal interception based on correlation detecting technology
Wei Weidong, Hu Wei, Sun Xiaoquan
2013, 42(4): 915-920.
[Abstract](258) [PDF 752KB](273)
To keep a balance between the detection probability and the false alarm rate(FAR) in the design of a scattered laser warning receiver, both theoretical and experimental studies were conducted to investigate the correlation detecting technology suitable for the scattered laser warning. On the basis of the analysis of the irradiance distribution and characteristic in time domain of the 1.06 m aerosol scatter in the low atmosphere, the theoretical sensitivity of the laser warning receiver(LWR) based on the correlation detecting technology were educed according to the experiment results of the improvement of signal-to-noise ratio and the corresponding operating condition of a correlation element. Then a scattered laser pulse correlation detector was developed, and the off-axis interception of aerosol scatter was achieved in the outdoor experiment. The research work demonstrates that applying correlation detecting technology to the interception of the aerosol scatter is effective in improving the detection probability of a LWR without the rise of the FAR.
Laser Doppler velocimeter based on dual-longitudinal-mode He-Ne laser
Liu Changqing, Nie Xiaoming, Fu Yangying, Zhou Jian
2013, 42(4): 921-924.
[Abstract](376) [PDF 728KB](193)
In order to make the measurement for high speed and super speed, a novel structure of Doppler velocimeter based on the dual-longitudinal-mode He-Ne laser was proposed. The principle of the dual-longitudinal-mode laser Doppler velocimeter was expounded while the optical schematic of the system was designed. And the Doppler signal was processed using the digital filtering and autocorrelation. Results of the theory analysis and experiment show that the dual-longitudinal-mode laser Doppler velocimeter reduced the scale factor highly using the beat frequency of the adjacent two longitudinal-modes as the basic frequency and solved the problem of high speed and super speed measurement; basement and part of noise are get rid of with the help of the digital filter; noise is restrained further with the method of digital autocorrelation so that the signal-to-noise ratio is raised and the Doppler frequency is extracted easily. The tangential velocity of the measured point in the rotating disc was obtained and the repeatability of the results was good to 0.8%.
Influence of linear gain modulation lidar system parameters on range accuracy
Zhang Yong, Cao Xibin, Wu Long, Zhao Yuan
2013, 42(4): 925-929.
[Abstract](286) [PDF 709KB](246)
Range accuracy is one of the most important parameters in a radar system. Research on the influence of range accuracy has an important value to improve the laser performance of radar. As a novel lidar system, linear gain modulation scannerless lidar acquires range information from image intensity by using the technique of range-intensity mapping. The relationship between range resolution and lidar system parameters was under investigated, taking different factors into consideration, including the modulation error of ICCD, the photonic noise at low echo intensity, the detector noise, and the gain saturation of micro channel plate. This paper presents that, within a certain region of echo signal power, range resolution can be improved by over twice that of outside the region, leading to great improvements of lidar system performance.
Semi-physical simulation platform of filter bandwidth of modulated lidar on optical carrier
Zhou Bo, Liang Kun, Ma Yong, Li Shaohua, Li Jing
2013, 42(4): 930-934.
[Abstract](376) [PDF 706KB](153)
It has been proved that backscatter can be significantly reduced under water detection when laser source was modulated to be of narrower pulse at the emitter and echo was detected by narrow-band filter at the receiver. In practical applications, filter bandwidth is the key parameter for suppression of backscatter when modulation frequency has been determined. Based on previous study on seawater parameters and pulse frequency expanding characteristics, an ocean modulated lidar semi-physical simulation platform was established to study filter bandwidth. It is concluded that target contrast will firstly increase and then decline slowly with the increase of filter bandwidth. By comparing the experimental results, a method of filter bandwidth design was presented.
Optical design and enhanced output of a surface-emitted THz-wave parametric oscillator
Li Zhongyang, Li Jiwu, Bing Pibin, Xu Degang, Yao Jianquan
2013, 42(4): 935-939.
[Abstract](337) [PDF 641KB](143)
High-power tunable terahertz wave(THz-wave) radiation was parametrically generated via a surface-emitted THz-wave parametric oscillator(TPO) pumped by a multi-longitudinal-mode Q-switched Nd:YAG laser. The effective parametric gain length under the condition of noncollinear phase matching was calculated to optimize the parameters of TPO. The THz-wave radiation from 0.77 to 2.83 THz was obtained. The maximum THz-wave output is 347.8 nJ/pulse at 1.78 THz when the pump power density is 222.3 MW/cm2, corresponding to the energy conversion efficiency of 3.9110-6. The far-field divergence angle of THz-wave radiation is 0.020 4 rad at vertical direction and 0.006 8 rad at horizontal direction.
Dispersion and compensation of femtosecond laser pulses in the atmosphere
Shen Zhenmin, Liu Hongying, Lan Tian, Li Shaohui, Ni Guoqiang, Liu Haojie
2013, 42(4): 940-946.
[Abstract](367) [PDF 838KB](519)
Satellite femtosecond laser ranging can theoretically achieve the ranging accuracy in the order of submicron, but femtosecond laser pulse duration broadening caused by the dispersion when it propagates in the atmosphere significantly makes the ranging accuracy decreased. To compensate the dispersion, the dispersion amount of femtosecond laser was calculated in the atmosphere. The group velocity dispersion formula and pulse duration broadening formula of femtosecond laser pluses in the atmosphere were derived. The results show that laser pulse broadening is determined by the group velocity dispersion and the propagation distance. Also shows that the dispersion is much larger when the pulse duration is much smaller under the same center wavelength, and the dispersion is much larger when the center wavelength is much smaller under the same pulse duration. Calculate the group delay, the group velocity dispersion and the three order dispersion in the atmosphere and BK7. The satellite femtosecond laser ranging system should adopt femtosecond laser with a longer center wavelength of 1 550 nm, and the pulse duration should be properly selected. Because femtosecond laser pulses have large dispersion when it transfers in the atmosphere, the dispersion compensation method is given by using single mode fiber sequence for the coarse compensation and grating pairs for the fine compensation.
Determination of Cr and Pb in soil by laser-induced breakdown spectroscopy
Chen Jinzhong, Bai Jinning, Song Guangju, Sun Jiang, Wei Yanhong
2013, 42(4): 947-950.
[Abstract](329) [PDF 750KB](200)
To examine the capability of laser-induced breakdown spectroscopy on detection, soil plasma was deduced using Nd: YAG laser under optimal conditions, and then the content of element Cr and Pb in the national standard soil samples was analyzed by the method of plasma atomic emission spectrometry. The calibration curves were respectively drawn with Fe atomic spectral line, spectral lines background and nothing as internal standard. The precision and detection limit of the method were established. The results demonstrate that the values of relative standard deviation of element Cr are 5.85%, 26.48% and 33.10%, and the corresponding values of Pb are 5.42%, 22.78% and 38.66% respectively under these three conditions, which indicates that the internal standard method can improve the precision of the measurement. The detection limits by Fe atomic line as internal standard are 3.5010-3% for Cr and 57.9010-3% for Pb, which meets the requirements of trace element analysis.
Advanced optics
Anti-jamming design for multi-velocity imaging mode of multiple TDI CCDs mosaic remote camera
Qu Hongfeng, Wang Xiaodong, Xu Shuyan, Bao Haiming, Li Bingyu, Lv Baolin
2013, 42(4): 1026-1032.
[Abstract](318) [PDF 944KB](251)
TDI CCD imaging circuits had been interfered by each other in multi-velocity working mode. There were jamming inclined strips whose slopes varied with raw frequency on the image of that mode.The original circuit design system was detailedly analyzed and optimized to solve this problem.First, the phase difference in various line cycles had been analyzed. Since there were many differences in every line cycle of various CCD imaging timing, the interference was different between some pixels and other pixels of every line in multi-velocity working mode. The interference difference of some pixels was the reason that causes jamming inclined strips. Then, those problems were solved by these methods, such as the optimized routing of critical signals, adjustment of ground and power layout, and improvement that the decoupling capacitor connected into ground. Finally, imaging circuits were tested after improvement. The results indicated that jamming inclined strips were eliminated. Image RMS noise wasreduced from 21.5 mV to 4.2 mV. The experiment showed that the use of anti-jamming technology effectively reduced the channel interference and improved image quality.
CFRC outer baffle structure & modal analysis and test of space camera
Chu Changbo, Chai Wenyi, Zhang Haosu, He Tianbing, Wen Desheng
2013, 42(4): 1033-1037.
[Abstract](241) [PDF 923KB](285)
Outer baffle of space camera was designed and manufactured with more complicated shape and multilevel inclined vanes using high strengthened carbon fiber reinforced composite(CFRC) T300. Meanwhile the manufacturing process was introduced briefly. Modal analysis was finished with finite element method(FEM). Fixing the outer baffle on an existing fixture the modal test was finished and the radial modes and shapes were obtained, the test frequency response function map was also presented. Comparing the finite element analysis(FEA) and testing data it is indicated that the error of every mode is less than 2.3% between the FEA model the fact product. It can be seen that the structure of CFRC outer baffle is reasonable and the FEM is feasible. Used into the kinetic modeling process of the space camera, the FEM could have guidance significance to the design of the whole structure of camera.
Application of auto-focusing with margin field for airborne remote sensor
Zhang Jichao
2013, 42(4): 1038-1043.
[Abstract](214) [PDF 921KB](247)
To solve the problem of auto-focusing in large array airborne remote sensor, a method to search position of focal plane in center field through auto-focusing in margin field was presented. Combination of oblique assembling and fine setting were taken to improve precision of auto-focusing, which could settle the influence of field angle in margin field. Microscope adjustment, photographic adjustment and electric adjustment were used to realize coarse calibration, accurate calibration and fine calibration of focal plane position and the problem of difference between focal plane position in center and in margin field was resolved. In servocontrol of the auto-focusing system, coarse-to-fine and ergodic hunting method were taken to find the optimum position of focal plane. Minimum step length was 0.01mm, and repeatability precision was 0.03mm, which was within focal depth and met the requirement. After experiment and flight test, focal plane that was detected by this method was accurate and the photographs were in high quality.