2014 Vol. 43, No. 9
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2014, 43(9): 2787-2792.
A new design of optical switch composed of a vanadium dioxide(VO2) thin film and embedded sub-wavelength metallic gratings was proposed. The numerical calculations of the device performance were carried out using the Finite Element Method (FEM). This design exhibited broadband and polarization selective all-optical switching effects in the near-infrared spectrum. The embedded gratings enhanced the extinction ratio of the VO2 film, and achieved high extinction ratio in sub-wavelength device size. The optical properties of the proposed design depended little on the incident angle. In addition, the transmittance and absorbance can be tuned by the geometric parameters. The device has great potential usages as the infrared spectrum is of great important both in optical communication and computering, and optical imaging in military reconnaissance and industrial non-destructive detecting.
2014, 43(9): 2793-2797.
Resistance selection of blind element used in linear photoconductive (PC) PbS detector for counteracting background current was analyzed. It was found that the blind element resistance can be chosen to be same as, or to be a fixed ratio to that of relevant sensitive element. And the ratio should be equal with ratio of biases applied to blind element and relevant detector. Two linear PC 1 128 PbS infrared focal plane array (IRFPA) detectors, with sensitive element size of 100 m 100 m, and blind element size of 100 m 100 m and 200 m 50 m, were fabricated and their performance were tested by IRFPA test system. Results show that when the working condition satisfied average responsivity and average detectivety are same for using different blind elements. Results validate the feasibility that background output uniformity improvement of IRFPAs by tuning the resistance of blind element.
2014, 43(9): 2798-2804.
HgCdTe electron injection avalanche photodiodes(e-APDs) work in linear mode. A weak optical current signal is amplified orders of magnitude due to the internal avalanche mechanism. The design of digital ROIC with a column-shared ADC for cooled (77 K) hybrid e-APDs FPA was presented in this paper. Sigma-delta conversion was a promising solution for high-performance and medium size FPA as 128 128. A multistage noise shaping (MASH) 2 -1 single bit architecture sigma-delta ADC with switched-capacitor circuits was designed for column-shared ADC. A cascaded integrator-comb (CIC) filter was designed as the digital decimator filter. The circuit was implemented in the GLOBALFOUNDRIES 0.35 m CMOS process on the basis of a 100 m pixel pitch. A quantization noise subtraction circuit in modulator was designed to subtract the quantization noise of first-stage modulator. The register word length of the filter in each stage was carefully dimensioned in order to minimize the required hardware. Furthermore, the digital filters operate with a reduced supply voltage to 1.5 V. Simulation results showed that the sigma-delta conversion achieved the resolution higher than 13 bits and 2.4 mW power consumption per ADC at 7.7 k Samples/s rate.
2014, 43(9): 2805-2809.
With the development of InSb large-scale Infrared Focal Plane Arrays (IRFPA), wet etching process has not met the new technological requirement of IRFPA. A novel wet etching process was expatiated with suitable ratio citric acid/H2O2 as etchant instead of lactic acid/nitric acid in being and assistant etching facility using N2 agitation. The results from comparison and analysis of the experiment clearly indicate that the surface morphology etched by new process, compared with the conventional process, has less lateral etching and mesa trench, more surface uniformity and lower roughness. Otherwise, the electrical properties is improved with lower leak current.
2014, 43(9): 2810-2814.
The research of the infrared stereo feature of ground target is useful for describing the detail of infrared feature, and it plays an important role in the field of infrared image simulation,infrared target recognition and controlling the target infrared radiation to realize infrared camouflage and so on. In this paper, the various factors that influence the target surface temperature were analyzed, then the model for the calculation of target surface temperature was introduced. The relation between temperature and time for some building wall outside surface by daylight was calculated using one dimension heat conduction differential equation. It proves that the calculation method is correct according to the comparison between the result value and the measured value. On the basis of the calculation of temperature, the infrared radiation was calculated and discussed. The result shows that the infrared stereo feature of ground target is more obvious in day than in night.
2014, 43(9): 2815-2818.
Because of the limits of illumination in the cars, the drivers can't observe clearly at night, which greatly increases the driving dangers. Car night vision system is a novel technology that helps to increase the driver's observation distance and is not subjected to the adverse conditions such as snow and rain. Novel car night vision system has has been widespread concerned. However, the change of temperature has a great impact on night vision system. Chalcogenide glass has a high-transmittance rate in infrared spectrum regions, and also has the advantages of small temperature coefficient of refractive index and modling which is suitable to car night vision systems. The features of chalcogenide glass were analyzed, the advantages of chalcogenide glass in night vision system were summarized. Car night vision systems using chalcogenide glass were presented.
2014, 43(9): 2819-2826.
When to detect an air target in infrared, bird is a potential source of false alarms, its IR characteristics are similar to the target's. The way to calculate the signal of the bird and target on the detector was firstly discussed, and the effects of the IR system's focus position were specially considered. Secondly, the influences that the flight altitude, area and focus position of system have on the bird's signal on the detector were analyzed according to the obtained formula. The signal of the target was also analyzed through the same way. The results show that the bird and the target can not be discriminated by the signal characteristics. Lastly, the way to discriminate the bird and the target was proposed based on the velocity, and the formula of probability that the bird would be treated as a false alarm was deduced and the calculation examples were done. From the results, it can be seen that the bird can be eliminated largely by the differences in velocity.
2014, 43(9): 2827-2831.
Dim target fusion detection in dual-band IR image is one of the key technology and research hotspot of infrared homing system. In order to establish an effective fusion-detection structure, the Boolean logic rules based fusion algorithm was analyzed. According to the principle of dim infrared target imaging, a hybrid fusion detection algorithm with AND logic and local gray was proposed based on the full use of local gray feature of dim target. First of all, infrared image of each band was segmented. Secondly, the detection results of two bands were fused using AND logic. Thirdly, to improve the probability of detection, the point beyond AND logic was determined using local gray feature. Finally, in order to optimize the local detector, the segmentation threshold in the first step was adjusted based on the fusion results. Simulation results show that the algorithm can improve the dual-band infrared detection capabilities effectively. Further, the algorithm features simple architecture and high computation speed, which makes it highly practical.
The molten pool convection has a great impact on elements and pores distribution during the laser cladding process. In this paper, the form of molten pool convection was investigate in terms of laser cladding NiCuFeBSi alloys on the substrate of gray cast iron and 45 steel. Results indicated that the distribution forms of pores and elements in the clad layer are uniform and dispersive due to the molten pool convection. Moreover, element distribution is also uniform without any slow transition from the bottom of clad layers to the top by means of electron probe microanalysis (EPMA). And according to the Gaussian distribution of energy in the YAG laser beams, it can be concluded that the driving force of convection is the surface tension gradient due to the non-uniform distribution of molten pool temperatures. Those of the laser thermal density, the molten pool temperature, the convective speed and the surface tension gradient are closely related with each other. It indicates that the temperature increases as the laser thermal density rising. The higher temperature is, the larger surface tension gradient will be as well as the convective speeds.
2014, 43(9): 2840-2843.
An all -fiber high power supercontinuum laser source was experimentally reported. An ytterbium-doped ring fiber oscillator was established as the seed source. By utilizing a three-stage master oscillator power amplifier (MOPA), the signal light average power was amplified to 62 W with a central wavelength of 1 065 nm, the 3 dB spectral bandwidth was 15 nm, and the repetition rate was 118 MHz. By coupling the amplified pulsed laser into a piece of photonic crystal fiber(PCF) with a 1 040 nm zerodispersion wavelength, supercontinuum with 28W output average power was obtained, the spectrum range was covering from 600 nm to 1 700 nm, and the optical conversion efficiency is 45%. In this experiment, the coupling problem between large core doped fiber and photonic crystal fiber at high output power was also solved.
2014, 43(9): 2844-2848.
The experimental system for laser -induced acoustic signals had been built for research on characteristic of laser-induced plasma acoustic signals. Acoustic signals were produced by pulsed laser focusing into water. A hydrophone was used to receive the acoustic signals. A high speed camera was used to record the breakdown procession. Time and frequency domain of laser-induced plasma acoustic signals were studied. Its directivity and transmission characteristic were analyzed theoretically, and proven by experiment. The results are as follows: The pulse width of laser-induced plasma acoustic signals is about 20 s, its frequency width is 500 kHz and main frequency is 70 kHz. It transmits in all directions and decreases proportionally to 1/r, main frequency decreases as distance increases.
2014, 43(9): 2849-2853.
An experimental research on self-phase modulation (SPM) of high power picosecond pulse amplifier was conducted by high-power all-fiber picosecond pulse fiber laser with an MOPA configuration. The seed source is a self-built fiber laser passively mode-locked by semiconductor saturable absorber mirror (SESAM). To avoid nonlinear effect, the repetition rate of the seed pulse should be increased to 328 MHz through a self-made repetition multiplier before amplification. The amplifier employed a three-level amplifying structure and finally received a stable picosecond pulse laser output with a center wavelength of 1 066.5 nm, a 3 dB spectrum width of 2.5 nm, and an average power of 91W. In the experiment, there was research on change of spectrum caused by SPM in the process of amplification. An analysis of the output spectrum of the laser demonstrates that with the increase of power, the influence of the initial chirp and the shape of the pulse on the SPM effect of high power fiber laser becomes deepens. In the mean time, it is also influenced by self-steepening effect.
2014, 43(9): 2854-2859.
Low contrast target detection is important in the applications of evidence gathering, protection from terrorists, remote surveillance, search and rescue, but it is difficult to detect by traditional imaging techniques. 2D/3D range-gated imaging(RGI) was proposed to detect low contrast targets. In our method, 2D range-gated imaging can output two-dimensional gate images of targets with background filtered or partly filtered to silhouette targets and simplify image processing of target extraction. If background is complex in gate images, 3D range-gated imaging can further reconstruct the spatial depth information collapsed in two-dimensional gate images, and then target can be easily distinguished from background by the depth map of target in a scene. Note that 3DRGI is realized by supperresolution depth mapping only based on the data of 2DRGI and there is no need to take time to get new data like depth scanning. Therefore, real-time performance is improved, and data volume is also reduced. Our research and experiments demonstrate that 2D/3D range-gated imaging is effective for low contrast target detection, even under low light or bad weather conditions.
2014, 43(9): 2860-2866.
The SAR/GMTI in wide-swath can be obtained by reconstructing virtual space samplings of MIMO-SAR into equivalent observation channels. Based on the properties of the configuration of wide- swath MIMO-SAR, the echo signal of moving target was firstly studied to reveal the distinctness with the echo signal of traditional SAR system. The effect of the echo signal of moving target in MIMO-SAR was also studied using paired echo principle (PEP). This analysis decomposed the echo signal into equivalent micro-motion phenomenon, which had a similar characteristic with micromotion target. Then, the expected time-frequency spectrum of MIMO -SAR in wide-swath was discussed in detail. Finally, numerical simulations give the validity of conclusions.
2014, 43(9): 2867-2872.
By right of its non-diffracting and self-constructing property, Bessel beam has gained growing attentions from scholars since its naissance. Based on the generalized Lorenz-Mie theory (GLMT), the incident on-axis Bessel beam and scattered fields of the chiral sphere were expressed in terms of the spherical vector wave functions (SVWFs). The analytical solution to the scattering of chiral sphere illuminated by an on-axis zero-order Bessel beam was investigated by utilizing the SVWFs and continuous boundary conditions. The on-axis Bessel beam was degenerated to a plane wave incident on a chiral sphere, and the results were found to be in good agreement with the literature available. The effects of beam, particle parameters, and on-axis beam waist center shift z0 on the scattered intensity were numerically analyzed. The theory present here may play an important role in the fields of the applications of chiral material and chiral-coated target in microwave engineering and shielding targets.
2014, 43(9): 2873-2877.
The power of the 13.5 nm (2% bandwidth) emission is one of the key parameter for the EUV source. It's important to study the temporary of the plasma in the capillary, which is useful to optimize the discharge structure and the EUV source power. In this paper, the pinch process of the plasma and the collection efficiency under different inner radiuses of the capillary were calculated theoretically. And the influence of the inner radius of the capillary on the dynamic condition of the 13.5 nm (2% bandwidth) emission was detected by a EUV monitor, which was used to analyze the influence of the inner radius of the capillary on the pinch process of the plasma. By combing the theoretical and experimental results with the design of collectors in this system, the 13.5 nm (2% bandwidth) emissions at the IF point were calculated under different inner radius of the capillary. The results show that the optimal of the power at the IF point has been got with the inner radius of the capillary 7 mm, the Xe gas pressure 7 Pa and discharge current 28 kA.
2014, 43(9): 2878-2882.
Camera sorters are used both for food and non-food applications like french fries, shrimps, vegetables, snacks, raw cotton, plastics, etc. But invisible foreign bodies, such as glass, or defects with exactly the same color as the product may not be detected. So the laser scanning system is used for detecting defects when the products and the defects have the same color. A laser sorting system is designed and improved based on the selective absorption principle. And a high-speed signal sampling experiment and a imaging experiment for the system were tested. By the selective absorption sorting technology, both products and foreign bodies were identified efficiently in the signal sampling experiment. The headline in the newspaper was selected as the imaging experimental sample and the diameter of scanning spot was adjusted close to 0.35 mm. The scanning data recorded through computer program was imaged by software. The resolution of the experimental result is 180*43 pixel. Imaging results illustrate that defects (1.5 mm) can be recognized accurately. Finally, after optical scanning system was analyzed, the phenomenon was found that most of the flux was lost due to the non-perpendicular illumination of the sample. A curve scanning sorting structure was proposed for improving traditional sorting system.
2014, 43(9): 2883-2888.
Taking ground-based laser irradiating flying target as the background, the encounter scenes were established which included head on irradiating scene and transverse irradiating scene. Considering the varying of irradiating area and power destiny distributing, the laser irradiating parameters were solved, and the heat conduction model was established. The numerical simulation of three-dimensional temperature field of flying target was calculated by the finite volume method. The influence of target moving on temperature field was analyzed. Different from laser irradiating stationary target, the varying of irradiating parameters has a great influence on temperature field distribution. As the target moving, the values of irradiating area decrease gradually, and the values of average power density and the rate of temperature rising increase gradually. The spacial profile of laser beam and temperature rising area are different because of the difference of angle between laser beam and target.
2014, 43(9): 2889-2895.
The microstructure and mechanical properties of TC17 titanium alloy with and without laser shock peening (LSP) were examined and compared. The titanium alloy samples were laser shock peened with different impacts at the same power density. Microstructure, microhardness and residual stress of TC17 titanium alloy introduced by LSP with different impacts were discussed by scanning electron microscopy(SEM), transmission electron microscope(TEM), X-ray diffraction(XRD), residual stress tester and sclerometer. The results indicate that a great deal of high-density dislocations and grain refinement are generated in the material surface layer. After 3 impacts LSP, there are nanocrystals in the LSP zone. The microhardness and residual stress value increase with greater impacts, and the variational trend with the depth is the same. Compared with the unsettled samples, the microhardness of TC17 titanium alloy treated by 5 impacts LSP has been increased by 20.7% at the surface, with a 300 m depth affected layer. A high compressive residual stress about 644.3 MPa is introduced with an increasing plastically affected layer by 5 impacts, and the affected depth increases to 1.9 mm.
2014, 43(9): 2896-2900.
To study the reflectivity character of alloy steel under CW-laser irradiation, the integrating sphere reflectometer was setup to measure the reflectance and temperature of 45# steel in -situ. Experimental results show that the reflectance dropped dramatically first, and then fluctuate periodically. The amplitude decreases and the period increases with time. With the increase of laser power, the temperature correspond to the begin point of decline and minimum point increases too. The number of maximum value is increased, the maximum value is increased one by one instead of decreased. A multilayer oxide films affection theory model was built. Combining with the model and oxide film growth mechanism of 45# steel, the reflectance was calculated at different oxide film structure and thickness ratio. The comparison between simulation and experimental results shows that the theory is reasonable. The study indicates that the multi-beam interference effects and absorb effects induced by oxide film growth are main reason of the reflectance evolution. In three layers of FeO-Fe3O4-Fe2O3, the absorbing Fe3O4 film is the dominant layer, the outer film Fe2O3 can cause multi-beam interference, and the inner FeO film hardly has contribution to reflectance.
The folded waveguide structure which has enormous advantages can been applied into THz TWT. In the article, a simple theory and equivalent circuit theory were used to analyze high frequency performance of 0.85 THz FW -TWT, and the CST MWS and HFSS codes validate these equivalent theories. The results of simulation and theoretical calculation were coincident. Because FW is a special slow-wave structure, the highest DC voltage was got. In deviation of fabrication dimensions, optimization structure parameters which make 0.85 THz FW-TWT to have wide band and high impedance were got. The results show the limited DC voltage is 26 kV and r0/a(r0represents beam hole radius and a is the width of FW) is about 0.1. The largest cold band width is about 400 GHz and the band width in flat dispersion region is about 275 GHz (825-1 100 GHz) and the change between the lowest and the highest phase velocity is below 1%. The design approach can been used to guide the design of slow-wave structure of THz FW-TWT.
2014, 43(9): 2907-2911.
A design new method about 0.14 THz power divider based on 3 dB directional coupler was presented. As THz device's dimension is micro -miniature, especially the key structure such as power divider's, it is extraordinary difficult to fabricate by precise machining. Traditional 3 dB directional coupler has 90 electric bridge structure, whose length between coupler slots is only less than 0.5 mm. This size nearly cannot bear the machining stress in processing. By means of analyzing the phase relationship between the direction coupler's branches, it is known that if the length between coupler slots increases only half-wave length's integer-multiple, the phase contrast between branches is still 90. As a result, the bandwidth is sacrificed. Since the dimension of coupling slot increases, this structure makes precise machining easy, and it has a band width about 10% at least yet. Analysis of simulation result provides the verification. The measured insert loss from 0.133 THz to 0.147 THz is less than 1 dB, and the return loss is less than -20 dB.
2014, 43(9): 2912-2918.
Terahertz (THz) frequency range provides information which are generally absent in microwave and optical images, so there are unique advantages with THz imaging for applications, both in science and beyond, such as military, security and safety screening, biological and medical analysis, non-contact materials testing, etc. However, compared with visible light, X-ray, infrared, laser, ultrasonic, etc, THz imaging is the latest development in the imaging field. Moreover, the terahertz electromagnetic scattering model and terahertz inverse scattering imaging method are mostly from well-studied fields: the Geometrical Theory of Diffraction (GTD) and Inverse Synthesis Aperture Radar (ISAR), Born/Rytov Approximation and Computer Tomography (CT), for example. Recent studies show that the mechanism of THz inverse scattering imaging cannot be accurately described by radar or tomography respectively. It may be said that there is a terahertz gap in inverse scattering imaging. In this paper, the relationship between radar imaging and tomography are briefly presented. The radar images have a response in which a few bright points dominate the image, because of isotropic point scattering mechanism. In contrast, tomography contains significant diffuse scattering components, providing fill to the images. In order to get more of a diffuse-like image that is more readily recognized and interpreted by humans, the improved method based on Range-Doppler(RD) algorithm is investigated. Finally, the 0.14 THz radar initial results are presented.
2014, 43(9): 2919-2924.
Sulfamethoxazole (SMX), one of the well-known effective and tolerable antibacterial agents, is widely used to treat urinary tract infections. Due to the variations in crystallinity structure, SMX exist in two different polymorphic forms I and II. These polymorphs have the same chemical composition but unique physio-chemical properties which will influence the corresponding different stability, solubility, dissolution rate and also other performance characteristics. Terahertz time-domain spectroscopy(THz-TDS) becomes a promising analytical technique relevant to the pharmaceutical and biological fields. THz-TDS measurement is able to characterize and distinguish the different polymorphs according to the rich information yielded, due to the sensitivity of THz absorption in this low-frequency region to the structures over length scales greater than intramolecular bond distances. In this study, absorption spectra in the terahertz region between 6 and 50 cm-1 (0.2-1.5 THz) were measured for SMX pharmaceutical molecule with different polymorphic forms (forms Ⅰ and Ⅱ, and also raw material) using THz -TDS technique at room temperature. The temperature-dependent THz-TDS of the raw SMX material was also investigated between 95 K and 296 K. Different absorption features were observed for these two model polymorphs. The observed THz absorption bands are strikingly sensitive to the change of subtle conformational structures existed within such crystal molecules with different polymorphism. The results show that the THz -TDS technique is a promising method in solid-state analytical tools to distinguish or differentiate such compounds with different polymorphs in pharmaceutical and biological fields.
2014, 43(9): 2925-2928.
The polarization characters of terahertz emission from air plasma produced by few cycle circularly polarized laser pulses were studied. Terahertz waves were generated from the air plasma produced by focusing the 8.6 fs circularly polarized laser pulses into the air. By measuring the polarization of terahertz waves and the relationship between the polarization and the carrier-envelope phase of driving laser, new methods for terahertz polarization control were developed. The terahertz emission was measured to be elliptically polarized, and its polarization rotated with the carrier-envelope phase of driving laser. This is useful for terahertz polarization control and provides a way to measure the carrier-envelope phase of few-cycle laser pulses in the air.
2014, 43(9): 2929-2934.
To meet the requirement of Nano-scale dimensional metrology, length standards with features below 100 nanometers were indispensible instruments. The length standards with periodic length of 213 0.1 nm were successfully fabricated through atom lithography, which was connected to atomic transition frequency and thus retraceable to a constant measured with highly accuracy. For further improvement of the quality of these standards, the evaluation and optimization of collimating the atomic beam were described in this article. A knife-edge was settled to cut the atomic beam collimated by the laser Doppler cooling. The fluorescence of the beam was collected to calculate its angular distribution and equilibrium transverse temperature. The stimulated absorption rate was considered and discussed. Full angular width at half maximum as small as 0.544 mrad was observed, corresponding to temperature of 343.8 K. Several angular distributions were measured by changing the laser characteristics to optimize the collimation.
2014, 43(9): 2935-2940.
Based on the angular spectrum theory, an parameter optimization method of optical analog was deduced, which focused on the restrictive relationship between calculation parameters and the actual optical system, and it was validated by numerical calculation. By controlling the variables, the impact of sampling number and interval to detail error and contour error was studied, as well as the sampling parameters' near-field and far-field change of an optical system. The results shows that the parameters calculated from the sampling restriction obtain a more accurate simulation result, and the calculation error can be better explained; the selection of sampling number and interval is mutually conditioned, which also depends on the actual optical system.
2014, 43(9): 2941-2946.
Infrared imaging spectrometers are applied to volcano behavior detection, forest fire survey, urbanization effect analysis, terrestrial composition and change monitoring, and camouflage recognition. In this paper, based on Dyson relay, a long wave infrared imaging spectrometer with wavelength range of 7.5 to 10 m was designed, which used a concave diffraction grating as its dispersive element. Its F number reached 1.2, field angle of view was 18 and spatial pixel resolution was 1 mrad, spectral resolution was 50 nm and noise equivalent temperature difference (NETD) was less than 0.3 K. The size of this designed optical system was about 72 mm39 mm39 mm, and its modulation transfer function approached to diffraction limitation. It has advantages of high throughput, low inherent aberration, and compactness. Analysis of its stray thermal radiation shows that its own thermal radiation of optical- mechanical system can be effectively suppressed by use of real entrance pupil as cool stop and of cryogenic optics.
2014, 43(9): 2947-2953.
A novel method for light distribution based on the substrate with freeform surface is proposed. The freeform surface substrate is designed and stimulated by using the TracePro software. The stimulation results show that a large luminous intensity angle can be achieved by adjusting the LED chips directly onto the substrate with freeform surface. The half-intensity angle is 60, 25 bigger than using the tradition reflection cup. Furthermore, a lighting with high light efficiency and uniform illumination can be achieved by using this method. When a same average horizontal illuminance is created, it costs 25% less luminous flux and avoids 60% less luminous decay than using the traditional method. By adjusting the shape of the freeform surface to distribute the LEDs' light, not only the other patterns of luminous effects are conveniently get, but also a high quality of LED lighting can be achieved.
2014, 43(9): 2954-2958.
The aberration characteristics of refractive optical system with large relative aperture and long focal length were analyzed. And a lens with 300 mm diameter, 540 mm focal length, 500 -850 nm operating wavelength range, and 2field of view was designed. First, as the secondary spectrum was the most prominent aberration, the Petzval form was chose as the initial configuration, and after complication, the configuration with three components with large air space was used, which was good for aberration correction and element size reduction. Then the partial dispersion and abbe number of typical glasses were recalculated and modified for the used wavelength, and P-V map is draw, then the glasses with some secondary spectrum correction ability and fine optical performance were chose. Finally the secondary spectrum of the system is reduced to 0.06 mm, which show that the system is apochromat. The design results demonstrate that the MTF of all field of view at Nyquist frequency 39 lp/mm is higher than 0.8, and 80% energy of the system encircled in 8um, which is less than a pixel size, and the distortion is less than 0.1%. All indexes satisfy the commands of system.
2014, 43(9): 2959-2963.
In order to overcome the difficulty of manufacturing off -axis aspheric surface, the key technologies of fabricating and testing SiC aspheric mirror especially for off-axis asphere with abnormal shape were studied. The off -axis SiC aspheric surface was grinded and polished by DMG, FSGJ -2 numerical control machine and IBF, the contour and optical parameters were measured and controlled by the coordinate measuring machine and laser tracker. Finally, an example for fabricating and measuring a similar eight-square off-axis aspheric mirror with the aperture of 600 mm270 mm was given. For the purpose of testing the aspheric mirror by interferometry, a null lens compensator was specifically designed and developed. As results, the peak-to-valley (PV) and root mean square (RMS) values of the surface error are 0.219 and 0.018 (is 632.8 nm), respectively.
2014, 43(9): 2964-2969.
Ultraviolet (UV) warning technology is playing a very important roll in the field of military application. Based on the optimal working waveband of solar-blind UV optical system from 240 nm to 280 nm, an optical system was designed for missile approach warning. To enhance the received light energy, expand the detection range and simplify the system structure, aspheric surfaces and binary elements were adopted in the system. Only five elements were used to realize the focal length 50 mm and field of view (FOV) 43 degrees. iKon-L 936 from ANDOR company was selected as the UV detector, which has pixel size 13.5 m13.5 m and active image area 27.6 mm27.6 mm. After optimization, the maximum RMS radius is only about 11 microns, which is much less than pixel size of the detector and more than 86% of the light energy from each FOV is converged within the circle of radius 6.75 microns. The image quality shows the designed system can meet the working requirements of solar-blind UV optical system. If the focal length can be decreased, the FOV of the system can be enlarged further.
2014, 43(9): 2970-2980.
Time lens is based upon space -time duality and has been contributed much attention during the last decade as a widely used optical instrumentation. Improvement of time lens is always enhanced by development of photonics as both engineering requirements and theoretical driving. A historical overview of how this powerful framework had been exploited to develop ultra -fast optical instruments was presented. Current state of implementing time lens by phase modulator (PM), sum-frequency generation (SFG), cross-phase modulation (XPM) and four-wave mixing (FWM) were summarized and analyzed by mathematic description. Then, limitations of different implementations of time lens for applications above were analyzed, accordingly. In addition, pulse magnification and time to frequency conversion as the main applications for ultra -fast pulse measurement by time lens were outlined with emphasizing on the evaluation by performances including resolution and record length. Furthermore, some ultra-fast nonlinear principle including surface-plasmon enhanced ultra-fast second- and third-order optical nonlinearities in metallic nanostructure, strong third-order optical nonlinearity induced high efficient FWM in graphene as potential theoretical and technological opportunities to improve time lens were presented and discussed.
2014, 43(9): 2981-2985.
Nonlinear laser spectroscopy has been widely applied for species trace in the gas-media. Forward DFWM with a self-stability beam-spiltting system was demonstrated in iodine vapor at different temperatures and pressures. It is found that the effects of the variable temperature and pressure on DFWM spectra structure (555-556 nm and 558-559 nm) are vivid under the saturated pumping and probing situation, and first of all, a wavelength (555.1 nm) sensitive to temperature in the atmospheric pressure is found. Also the wavelengths(558.81 nm) insensitive to temperatures, which the wavelength can be used to measure the gas-phase media concentration at varied temperatures. Effects of different temperatures and atmospheric pressures on the DFWM spectroscopy in iodine vapor at atmospheric pressure are of importance to trace atom, molecular and radical in combustion diagnosis.
2014, 43(9): 2986-2991.
A construction method of wide angle test scenario based on the anechoic chamber was proposed. Utilizing the existing 42 RF array, the amplitude and phase of signals arriving at the receiver from array antenna units were calibrated by multi-state joint calibration. And by gray relational analysis principles, the proposed method achieved the approximately true mapping satellite constellation and dynamic interference in the anechoic chamber. So the semi-physical anti-jamming test environment whose largest field angle was 160 was constructed. Simulation and test results show that the maximal deviation between antenna units in the anechoic chamber and the angular domain of the satellite constellations in the real scene is within high gain 3 dB beam width, and the power needed for dynamic interference to arrive at the receiver is approximately the same whether at actual scene or under simulation in anechoic chamber. Lastly, the anti-jamming test of multi-beam receiver was completed, the relation curves of J/S and C/N0 were given, indicating that the proposed method can not only effectively simulate the outfield test scenario of satellite navigation receiver indoors, but also accurately test the performance of multibeam anti-jamming receiver.
2014, 43(9): 2992-2995.
The main polarization mode and coupling mode in polarization-maintaining fiber (PMF) have some optical path difference because of the internal birefringence. White-light interferometry for testing continuum polarized coupling distributing and discreting polarized coupling distributing in high birefringent waveguide was investigated. The polarization-maintaining parameter was obtained and a concise formula was derived. It can be used to measure the intensity and position of the coupling point accurately according to the relevant theory of modulation and demodulation. PMF and the optical fiber polarizer were measured as examples. The new approach can be utilized to test integrated waveguide elements, PMF, the axis alignment between birefringent waveguide, distributed optical fiber sensors, etc, The most prominent advantage of this method is to measure the polarization-maintaining parameter without any destruction to PMF. It can be used as an effective testing tool in PMF manufacture and application. With the help of this detection method, the performance of optical fiber polarization devices and optical fiber sensors is improved significantly.
2014, 43(9): 2996-3004.
Stability of wavefront aberration (WFA) has great impacts on imaging quality of space camera, which is a major performance index for those. With regard to possible gravity orientation and temperature range of space camera in manufacture and orbit, the mirror's tolerances and profile errors were calculated through FEA, and WFA was calculated by optical software using those. By simulating multi-orientation gravity states and adjusting environment temperature 204 in laboratory, WFA of the space camera was measured and tested, the average result changed from /14.7 to /12.4 at all states, the worst was /11 for single field. The testing data was nearly in accord with the calculate value, the mean range were -0.012 6 -0.003 1, the max difference error was -0.023. Moreover, the MTF to was tested validate the system stability, the result achieved 0.21, there were only 4.8% errors at choosing states. The method can be used to inspect and confirm the imaging performance stability, which has been used in wide-field TMA space camera, guiding design and finding week point, through analysis and testing, the data well illustrated the performance stability at all states.
2014, 43(9): 3005-3009.
In order to improve the centroid sensing accuracy of spot image of Shack-Hartmann wavefront sensor (S-H WFS), the error sources of centroid detection were discussed in the paper. The influence of detection window, threshold selection and centroid algorithm on centroid detection accuracy was analyzed. On this basis, detecting window selection method based on template match and adaptive threshold selection method based on single spot were proposed. The methods proposed in this paper were combined with the center of weight algorithm for improving the centroid detection accuracy. The accuracy with the comprehensive method increases 40% comparing with traditional method when signal-to-noise ratio(SNR) of the spot image of S-H WFS is more than 3. The methods was applied to a S-H WFS working in visible spectrum, the results showed that maximum centroid departure decreased from 0.83 pixel to 0.15 pixel. The work in this paper has a high value of practical application.
Atmospheric aerosol absorption capacity is a critical parameter determining its direct and indirect effects on climate. Accurate measurement is highly requested for study of the radiative budget of the Earth, photoacoustic spectroscopy is commonly recognized as one of the best candidates to measure the optical absorption coefficient (OAC) of aerosols. A Scanning mobility particle sizer (SMPS) and a homemade photoacoustic aerosol absorptionmeter were used to monitor the size distribution and OAC of the ambient aerosols at suburb of Hefei city, the real-time trends of OAC and size distribution in a serial time were acquired. Properties of the size distribution at different time which was classified into two distribution mode were analyzed in detail. The measured data shows that OAC has a well positive correlation with size distribution and number concentration of the atmospheric aerosol respectively and the emission of carbonaceous aerosol is the chief factor of the effect on OAC.
2014, 43(9): 3015-3019.
Standard model atmosphere is usually adopted in Raman lidar aerosol extinction coefficient inversion, but sometimes standard model atmosphere does not match the actual atmospheric density so cause a greater impact on the detection results. In order to reduce the influence to enhance Raman lidar aerosol extinction coefficient inversion precision, a new model which atmospheric density profile was determinated by the Boltzmann energy distribution and tropospheric temperature linear decline law was proposed to replace standard model atmosphere, Theoretical derivation and experiment verify the feasibility of the method, and the result shows that the new model is more consistent with actual atmosphere, so it can reduce the error, it is proposed Raman lidar data processing may use this new model.
2014, 43(9): 3020-3025.
In allusion to the deficiencies of traditional inertial celestial integrated algorithm and selection uncertainty of the NAVSTAR, an algorithm based on SINS/CNS deeply integrated navigation with single star was proposed in this paper for the navigation system of long duration aero crafts. The error characteristics of inertial navigation and the star observation of two -gimbal were modeled exactly, and the advantages of both were analyzed and synthesized, the data of single star observation angle and inertial navigation was fused with high accuracy completely. In the height channel, barometric altimeter was introduced for altitude error damping. The design of the Kalman filter achieved optimal estimation of INS error. With analysis of the system observability, optimal NAVSTAR selection criteria was successfully brought out, effective solution to the problem of declining performance of the algorithm in the part of the observation angle was solved effectively. The simulation results of the algorithm show that the long positioning accuracy is better than traditional algorithm. Optimal NAVSTAR selection criteria effectively improve the robustness of the algorithm, which has a higher significance to theoretical study and engineering application value.
2014, 43(9): 3026-3029.
Daytime space target laser ranging data can help improve the space target orbit determination precision, has important application value in terms of space research. During the daytime, the sky background is light, laser ranging echo signal is very weak, generally to identify the weak space target laser echo signal from the strong background light is very difficult. In allusion to weak signal detecting technical problem of laser ranging for space target in the daytime, influence of sky background noise in the daytime was estimated, ranging false alarm probabilities at various detection threshold was calculated, relation of detection threshold and laser ranging gate was analyzed, detection threshold requirement of laser ranging for space target in the daytime was presented, a weak signal detecting method of laser ranging for space target in the daytime based on multi-photon detector was put forward, and its feasibility was validated by experiment. This result can be used for designing daytime laser ranging system and researching new type laser ranging system.
2014, 43(9): 3030-3035.
In order to resolve the lower precision of optoelectronic theodolite dynamic measure precision, a method which is based on the correction of different delay time between the clock base and other sub - systems was proposed. The measurement theory and shipment of optoelectronic theodolite were introduced, the relationship between the object and the image was analysis. The reason which infects the precision were accuracy of camera inside azimuth element and the adjustment of optical distortion was pointed. And the reasons which effect the optoelectronic theodolite dynamic measurement were analysis, and the different delay time between different sub -system parameter were pointed. The correction and accuracy of the method were verified by test data, the average variance of optoelectronic theodolite dynamic error in horizontal and vertical were improved from 27.89 and 17.67 to 10.07 and 8.56. This method improves the dynamic measure precision of optoelectronic theodolite and is suitable for other optical electronic measurement system.
2014, 43(9): 3036-3041.
A novel optical sensor for simultaneous measurement of voltage and current is proposed and demonstrated in experiment. The optical sensing unit is only composed of single bismuth silicate (Bi12SiO20, BSO) crystal and two prism polarizers. The BSO crystal exhibits both Pockels electrooptic effect and Faraday magnetooptic effect, thus voltage and current to be measured can simultaneously modulate the probing light wave when transparent axes of the two polarizers are parallel or perpendicular with each other. The frequency of current sensing signal is the same as that of the original current to be measured, meanwhile, that of voltage sensing signal is doubled. Thus current and voltage sensing signals can be simultaneously separated and measured by using two band pass filters. AC current and voltage with industrial frequency in the ranges of 6 A and 200 V were simultaneously measured in experiment by use of single BSO crystal with a size of 6.04.02.9 mm3.
2014, 43(9): 3042-3045.
It is critical to extract the linear rotational invariant of an imaged target in passive ranging from the images, and it' s more difficult to extract the parameters from a general non-cooperative than from a cooperative ones. A method was presented to construct a virtual circle as the inherent rotation invariance of a circular target. The proposed virtual circle was the circumcircle of equilateral by triangles extended from three matched points in adjacent frames in the image sequence. It is demonstrated by the simulations that the probability density function curve of the proposed virtual circle has tighter error distribution than that of a few other methods, and further studies indicate that the diameter of this virtual circle is also a preferable depth-related line segment feature. The line segment feature is used for the target distance estimation and it displays superior performance. It is characterized by its simple for the distance estimation using line segment features, and the concept of virtual circle increases the flexibility in practice. Because as few as three matched points are the least points in target tracking based image feature, so it is attractive for passive ranging to non-cooperative targets. The method is valid under the condition of the inclination angle of target relative to camera increased or decreased from -10 degree to 10 degree between adjacent sampling times.
2014, 43(9): 3046-3050.
Au -doped Hg1-xCdxTe crystals were grown by vapor phase epitaxial method. The optical properties of Hg1-xCdxTe crystals were investigated by using Fourier transform infrared spectroscopy and Raman spectroscopy. Moreover, the surface of Hg1-xCdxTe epitaxial materials were observed by metallographic microscopy. Based on traditional photovoltaic technique, the shot-wavelength detectors were made by Au-doped Hg1-xCdxTe film materials. Performances of the detectors were favorable. The background-limited detective was 4.67E+11/(cmHz1/2W-1).
2014, 43(9): 3051-3056.
The gain fiber is the important indicators to determine the output power and beam quality of fiber laser. The paper focused on the large-mode-area fiber (LMA) bending effect on fundamental mode (FM) area and mode field distortion by numerical analysis, the FM area and gain coefficient of LMA fiber with different refractive index (RI) and doped distributions were solved by finite-element method. The Gaussian hybrid refractive index distribution and doping profile were proposed firstly. It can effectively improve the gain coefficient and suppression coefficient of high-order modes (HOMs). Moreover, the bending against of the fiber can be strengthen, the design can balance the contradiction the mode area and bending resistance. Based on the numerical calculation, the gain fiber with Gaussian hybrid RI distribution and doping profile were designed, the fiber diameter was 65 m. At the wavelength of 1.064 m, the FM area can be 1.17103 m2, the FM relative gain coefficient and relative suppressing coefficient can reach 0.58 and 0.208 8, the output and beam quality of the fiber laser can be improved effectively.
2014, 43(9): 3057-3060.
The method of Metal Organic Chemical Vapor Deposition (MOCVD) was used to grow GaAs/Al0.3Ga0.7As quantum well material. Which is prepared for quantum well infrared photodetectors (QWIP). The two sample-devices have large surface area 300 m300 m. But its pressure welding area of inside electrode is 20 m20 m while that of the one outside is 80 m80 m. Refrigerating machine of liquid nitrogen was adopted to do dark current test under variable-temperature from 77 K to 300 K. The dark current was studied under different bias voltages. The results show that dark current curves is asymmetric under positive and negative bias voltage. The crystal structure is investigated by use of high -resolution transmission electron microscope (HRTEM) to determine the exact reson. Which shows that there is thread dislocation and nonuniformity in different degrees. The follows is known from above: It is the phase separation caused by the threading dislocation that leads to photoelectric performance variation essentially. At the same time, it is interfacial asymmetry between AlGaAs and GaAs in different growing orders and the doping element diffusion that intensifies asymmetry of dark current.
2014, 43(9): 3061-3065.
In order to achieve the purpose of real-time atmosphere turbulence simulation by used liquid crystal spatial light modulator, A new computing method of liquid crystal atmospheric turbulence simulator real-time wave-front generation based on GPU has been proposed. According to the characteristics of liquid crystal turbulence simulator, which is high resolution, high precision, The Compute Unified Device Architecture was discussed in this paper. Furthermore, a wave-front generation model based on GPU was established with parallel optimization and share memory optimization. Finally, the experimental results by used CPU and GPU wave generation was given. The result shows that: the consumed time by proposed method is less than 2 ms for a Zernike polynomial with 231 wave-front values in resolution of 256256, which is two orders of magnitude less than that of CPU, fully meets the real-time wave-front generation requirements.
2014, 43(9): 3066-3069.
Polymeric electro-optic modulators with microstrip line traveling-wave electrode was designed, fabricated and tested. Assuming that the electro-optic coefficient 33 of the core polymer is 30 pm/V, the performance parameters of the designed modulator is half-wave voltage V=6.70 V. The modulator was fabricated using the second-order nonlinear optical polymer materials which contained the independently synthesized chromophores. The performance of the modulators in direct current (DC), low frequency and microwave property were tested. Using the different poling methods, the low frequency V values at 1.55m were 10.5 V and 4.9 V for corona poling and contact poling, respectively. The electro-optic coefficient of core layer material 33 was thus obtained as 21 pm/V and 45 pm/V. The extinction ratio was measured to be 24 dB. Microwave property of electrode system was also tested with a vector network analyzer, and S parameters reflected this electrode system with low microwave transmission loss and return loss.
2014, 43(9): 3070-3074.
The dynamic range of closed-loop fiber optic gyroscope (FOG) decreases with the accuracy improvent of FOG improving. Based on aided MEMS gyroscope, a method of increasing the dynamic range of closed-loop FOG was present in this paper. This method makes full use of the large-scale characteristics of MEMS gyroscope. According to the difference of detected angular velocity between MEMS gyroscope and FOG, the interference of series can be judged, which makes FOG work in multistage interference fringe through correcting the output by judging interference of series. The simulation results show that the proposed method can increase the dynamic range of closed-loop FOG effectively.
2014, 43(9): 3075-3080.
In free space optical communications, in order to get the self-symbol synchronization and fixed symbol length, a novel flag dual amplitude pulse position modulation(FDAPPM) was proposed. The symbol structure, transmission rate and error probability of the FDAPPM system over atmospheric turbulence-induced fading channel were presented. By using the maximum-likelihood sequence detection, the high SNRs asymptotic on the error probability of the FDAPPM was analyzed and the diversity order and SNR modulation gains were calculated. The performance of the FDAPPM was compared with the conventional OOK, PPM, FDPIM, FDAPIM and FDAPPM. Numerical results indicate that under the same turbulence condition, the FDAPPM possesses the advantages over the FDPIM and FDAPIM in terms of transmission rate and error performance. It also provides high transmission rate than the PPM and simplifies the receiver design owing to the built-in symbol synchronization. Moreover, it does not have insertion/deletion error in modem due to the fixed symbol length.
2014, 43(9): 3081-3088.
In allusion that classical Allan variance cannot highlight the nonstationary of stochastic errors of Fiber Optical Gyroscope (FOG), and Dynamic Allan Variance (DAVAR) can, but there was no theory which proved the validity and the effectiveness of DAVAR systematically. The DAVAR, a measure of the time -varying stability of FOG was presented and discussed. First, the classical Allan variance and DAVAR were mathematically defined, and then their behaviors were extensively tested on simulated and experimental FOG output signal. What' s more, FOG stochastic errors changes were quantitatively described by a two-dimensional method. Results prove the validity and effectiveness of the proposed new tool using for analyzing the stochastic errors of FOG. DAVAR analysis method not only can determine the coefficients of FOG stochastic error, but also can describe their non -stationary. DAVAR is a more comprehensive, more effective and more useful tool for judging FOG performance.
2014, 43(9): 3089-3093.
A new hybrid integrated resonant optical gyroscope was presented. All the passive optical elements were fabricated on a single silicon substrate. The active part, which concludes only the laser and photodetectors, was mounted to the waveguide with flip -flop process. The main advantage of the construction was removing the external modulator, and it brings the integration to a new level. For the proposed hybrid integrated optical gyro, an alternative modulation/demodulation method was described in detail. High frequency square waveform modulation wave was assigned to the injection current port of the laser to obtain the frequency modulation. When the gyro rotates, the resonator curve of the two directions departs, resulting in square-wave output, which can be detected to obtain the angular velocity. This work has a big contribution to the integrated optical gyro system.
2014, 43(9): 3094-3098.
Beginning with summarizing the technology of diffuse optical tomography and its difficulties, a new tomography model for highly scattering media was proposed. Various of complex physical processes would occur when light transported in highly scattering media, such as transmission, diffusion, reflection, refraction, diffraction, etc. All these complex physical processes were simplified into transmission and diffusion with the new model. Compared with the existing model based on radiative transfer theory, the new model is more simple, more intuitive, less amount of calculation and higher reconstruction accuracy. The work procedure of the new model was described in detail. A new algorithm of tomographic reconstruction for the model was also designed, and its implementation steps were described. The simulation experiment about the model and the algorithm is made to verify the effectiveness of the algorithm.
2014, 43(9): 3099-3104.
Imaging spectrometer was a kind of optical remote sensing instruments which combined image with spectrum. Grating imaging spectrometer can acquire data cube. When the sampling frequency and splicing was reasonable, because of the nonlinear about dispersive elements making spectral expansion, lead to the distortion of strip image, as well as the distortion of spliced image. The distortion feature points were extracted more accurate by using the gray gradient from the edge to the center and genetic algorithm. By choosing appropriate parameters, we established the support vector machine regression mathematical model to correct the distortion. Compared with the conventional distortion correction method. This method was able to balance effectively the error from the global and the local and improve the accuracy of correction. The calibration of error can be controlled within 0.5 pixels by experimental verification.
2014, 43(9): 3105-3109.
Ghost imaging has attracted a great deal of attentions due to it's nonlocal characteristic and imaging resolution breaking the limitation of diffraction. A study about the relationship between the pure phase object ghost imaging and the fluctuation of the source was reported. That the intensity fluctuations of the source can affect the information of the pure phase object which we get from the ghost image was demonstrated theoretically and experimentally: the more severely the intensity of the source fluctuates, the more information of the pure phase object we can recover from the ghost image. Moreover, the increase of the intensity fluctuations could lead to the growing deviation of the object information of ghost images which obtained from different samples.
2014, 43(9): 3110-3115.
Under the different color temperature of light sources, the colors of images obtained by CMOS image sensors will be different, it was likely to happen that it deviate from the real color, resulting in a decline of image quality, seriously affecting the effective of high -definition electronic endoscope. Proposes an auto white-balance algorithm based on achromatic surface detection, using the sum of RGB three -channel of each pixel to detect the achromatic surface. With the achromatic pixels set, the illumination chromaticity was estimated, and then correct the colors of image, through the diagonal transformation of endoscope image in real -time auto white -balance algorithm, modified the color deviation phenomenon. This real time, effectively algorithm eliminates the color deviation phenomenon caused by different illuminate condition, which is in accord with the color with the color characteristic of human visual system.
2014, 43(9): 3116-3121.
Ultrahigh resolution imaging system on geosynchronous orbit can get earth image with 1 m resolution, using diffractive membrane optics. Cable -Strut Deployable Articulated Mast in this imaging system is about 100 m long, and was tightly required for its deformation. The diameter of primary mirror is about 20 m, and its thickness is only a few micrometers. To meet the optical performance objectives, the distortion of the primary mirror need to be minimized. So the thermal control system for Deployable Mast and primary mirror becomes a tremendous challenge. Based on the survey results about deployable baffle and primary mirror with large-scale membrane, ultrahigh resolution imaging system was thermally analyzed, and thermal control scheme was designed. The temperature distributions of deployable conical baffle in four extreme working conditions were provided, and the simulation results show the feasibility of the designed thermal control scheme.
2014, 43(9): 3122-3127.
Traditional stereo matching based on global optimization is of computational complex which is poor to get accuracy matching result for the pixels in occlusion and depth discontinuity region. An efficient method of stereo matching was proposed, which was based on Tao stereo matching framework. Firstly, the initial matching disparity was obtained by the enhanced local method. Then occlusion and mismatched pixels were applied from reliable pixels using the robust method and named unreliable pixels, then reliable pixels and presupposition of disparity plane were used to refine the unreliable disparity. Finally, in order to improve the disparity accuracy in low texture region, an enhanced belief propagation method was used to optimize the refined initial disparity, which had adaptive convergence threshold. Experimental results demonstrate that our method can reduce the error matching rate effectively, improve the matching accuracy in occlusion and depth discontinuity region, reduce the computational complexity as well as improve matching speed.
2014, 43(9): 3128-3133.
Signal CCD/CMOS sensors capture image information by covering the sensor surface with a color filter array (CFA). For each pixel, only one of three primary colors(red, green and blue) can pass through the CFA. The other two missing color components are estimated by the values of surrounding pixels. The first step was to estimate interpolation direction taking advantage of the pixels in 55 template and use the optimal weighting factors to interpolate G components. The second step was to interpolate R(B) components at the location of B(R) using the interpolation operator based on two-dimensional rational function. The third step was to interpolate R and B components at the location of G components by color difference interpolation. Lastly, the iterative interpolation repeated until approaching the optimal results using variance-constrained condition. Through Matlab simulate experiments based on 24 Kodak images and the images captured from our camera, the proposed algorithm outperforms both in visual and numerical aspects.
2014, 43(9): 3134-3140.
While the star images were pictured by space-based platform, there was a simultaneous relative motion between the background and the camera. The moving small object cannot be obtained through simple frame difference between adjacent frames. Thus, it was difficult to had the space object inspection. Based on the analysis of star image model, proposes an image registration method via extracting feature points and then matching the triangle. Firstly, it was the pretreatment of the images, which was to had a single-frame image segmentation from the selection of optimal thresholds, in order to remove the background noise. Then, divide the stars according to area sizes. For those eligible stars, make the feature triangles, and acquire the parameters from the matching in the adjacent frames. In order to minimize the calculation, the ignorance of the background interpolation was only applied to star coordinate matrices. Finally, detect the moving trace of the object according to multiple-frame connection. As the simulation experiments indicate, in the sequence images, the method can real time inspection in a high detection rate and a low false alarm rate.
2014, 43(9): 3141-3145.
For the color fusion of low-level light and infrared images have the characteristics of strong real-time performance and a large quantity of data, a low-level light and infrared dual channel real-time image fusion system based on multi -core digital signal processor (DSP) and field programmable gate array (FPGA) was put forward. Cyclone IV FPGA of Altera Co.Ltd. with serial transceivers was chose to complete the image information collection, preprocessing and all kinds of control of peripheral equipment, while the newest 8 core high performance fixed point and floating point DSP TMS320C6678 of TI Co. Ltd. was used to realize image fusion. The data transmission was achieved between field programmable gate array and multi -core digital signal processor through the high -speed Serial RapidIO (SRIO) interface, and then color transmission in YUV color space as well. When the color information of the color image in the day light was passed to the fusion image, it was closer to natural color and could reflect richer scene information as much as possible. Experiment shows that this system can realize realtime image fusion and useful color transmission, is suitable for the color fusion system applications of the dual channel video natural sense in the dynamic scenarios.
2014, 43(9): 3146-3150.
To solve the problem that traditional Retinex cannot work well in large dynamic range smoke image enhancement, the reasons was analyzed and a new Retinex algorithm was proposed with self- adaptive grayscale stretching. A mathematical model was built to estimate the gray level range of smoke area by calculating local dynamic range and information entropy. By stretching the gray level range calculated and processing the image with Retinex of different scales, the enhanced image was got. Experiment shows that the method can increase the information entropy of large dynamic range image and enhance the contrast of smoke area.
2014, 43(9): 3151-3156.
An interval inversion method was proposed to retrieve phase information directly from single interferogram. Due to the sign ambiguity of inverse cosine, an inversion was needed in the phase interval of (,2). This interval estimation was translated to a problem of fold-line fitting that can be solved by a genetic algorithm. Further, the least square was employed to find an optimal linear carrier frequency for the final phase distribution. The method was applied to one-dimensional and two-dimensional numerical examples. Simulation results, compared with the methods of traditional Fourier transform and fringe analysis, demonstrate the effectiveness and the ease of use.
2014, 43(9): 3157-3161.
A method for sequence image generation of dim point moving targets in complex star background was presented based on STK/matlab software. Firstly, the starry background modeling process was analyzed; then, the satellite disturbance and noise that affected the point target imaging were detailedly discussed to make sequence images simulated closer to the real world; and besides the space target was modeled and its relative geometric relationship with the observation satellite was predicted by the STK software, at the same time the visibility of high earth orbit was systematically analyzed. In addition, a simple and convenient method to calculate the space target visibility criterion was given. By taking into account of various factors that impacted the visibility of high earth orbit target, the space target orbit prediction data was generated by STK and then matlab software was adopted to simulate the sequence image. It's useful in providing space environment for detection and tracking space target.
2014, 43(9): 3162-3167.
Star' s gray intensity wouldn' t follow 2-D Gaussian distribution when the rotational velocity exceeded the highest rotational velocity which would affect the processing precision of centroid of star spot. The analytical solution of motion trajectory of star' s centroid was simplified considering that the exposure time was short enough, and then the precision of the linear approximation was analyzed through simulation. The character of gray intensity of smearing star was analyzed based on the simplified trajectory, then a novel algorithm was proposed to estimate the degradation parameters of smearing star image. Through simulation and experiment, the validity of the proposed algorithm has been testified, the largest error of estimated blur length is around 0.8 of a pixel, while error of the estimated blur direction is about 2, feasibility of the proposed method has also been validated through simulations.
2014, 43(9): 3168-3172.
In the real IR detector, the high frequency non-uniformity is mostly expressed as the column or the row stripes and the low frequency non-uniformity is mostly expressed as the patchy pattern. In real application, the scene is towards one continuous monotonous direction and has different appearances of non- uniformity. Under this consideration, a scene-based non-uniformity correction technology was proposed, it not only fitted the situation mentioned above but also was realized on the small packaged, low power consumed real-time hardware system. These problems were solved by developing a new projection estimator for the registration with a criterion, and this algorithm was immigrated into a FPGA_based hardware system. This system is fully engineered for some particular usage. The performance of the proposed technology was tested by the evaluation indexes, and it demonstrates the actual effect of correcting the non-uniformity under a monotonous motion on the system. According to the practical application, this algorithm has the advantage of the strong ability to eliminate the image degradation and fast convergence speed.
