2013 Vol. 42, No. 1
2013, 42(1): 1-6.
The calculation of supersonic missile temperature distribution plays an important role in the study of its infrared characteristic. Two primary radiation points of supersonic missile-fuselage and plume, were analyzed deeply. A temperature distribution model of supersonic missile was built, and the feasibility was proved by simulation. Firstly, a theoretical model and semi-empirical formula were adopted to calulate the temperature distribution of supersonic missile. Secondly, in the model, the plume was disposed as supersonic circular symmetrical adiabatic isentropic airflow approximately. The distribution of air airflow parameters were calculated by the characteristic method line. Thirdly, a theoretic model and calculation method of the plume shape were established. Finally, taking one missile as an example, the computing model was used to compute the temperature distribution of supersonic missile. The results indicate that this is an effective method to calulate the temperature distribution of supersonic missile according to the comparison between the result values and the measured values.
The rapid development of infrared detection and infrared guidance technology poses more threat to the survival ability of aircraft. How to reduce the infrared radiation of the aircraft becomes one of the key technologies to improve the ability of stealth. The exhaust system of aircraft is the main source of infrared radiation. In order to study the IR characteristics of the aft fuselage skin, based on the discrete transfer method in the paper, the infrared simulation of the aft fuselage skin for a typical fight aircraft was carried out to analyze the infrared radiation intensity distribution of the aft fuselage skin for a typical combat aircraft with the ejector nozzle in 8-14 m band by the form of a combination of the computational fluid dynamics(CFD) commercial software and self-developed IR computing software. 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 taken into account. Finally, the IR intensity of the fighter were investigated using the cooling insulation way and low infrared emissive material. It was found that the temperature of the engine heat-affected zone of the aft fuselage of the fighter were reduced by 70 K, the IR intensity of aircraft declined by 9.1%, 15.4% and 17.5% in the infrared detecting main threat orientation of the head within 5, 30 and 60, and reduced by 18.9% in just below 90. The skin of the engine heat-affected zone were covered by low emissive material, the IR could be reduced by 20% in the font basis. The results of research in this paper are of considerable guiding significance and referential importance for designing infrared stealthy aircraft.
With the development of science and technology, infrared stealth technology has been widely used in new weapons and equipments, and it has become an important performance and significant feature of the modern weapon equipment. The birth of the infrared sensors for missile seeker applications becomes a major threat for various types of weapons and equipments, especially for infrared detectors. The threats to weapons were analyzed; infrared stealth performance of the various types of weapons and equipment and development of the infrared stealth was summarized; the sources of infrared radiation, control technology measure of IR and development tendency were briefly analyzed for fixed wing aircraft as the key, but also for helicopters, surface ships and ground weapon equipments. The test results prove that research and application of the infrared stealth technology are important to all kinds of weapons and equipments.
2013, 42(1): 20-25.
In order to fully reveal the influence of thermal interactions between the armored vehicles and ground background on ground background temperature and infrared radiation characteristics, the temperature and infrared signature model of armored vehicles and ground background were established, with focus on heat transfer between armored vehicles and ground. By introducing mechanical relationship between the road and the track, thermal and mechanical models between the moving vehicle and the road were established. Using method of the moving mesh, the subsidence phenomenon and thermal trace on the road after target vehicle moving were simulated. Based on the infrared radiation theory, considering the radiation, reflective radiation and atmospheric transmission characteristic, the thermal interactions and infrared radiation characteristics distribution of armored vehicles and terrain background under three different conditions were calculated. The simulated temperature and measured temperature in the experiment were compared. The model's precision was validated. The simulation results show that this method is crucial to the stealth design and stealth technology assessment of ground target.
As the influence of background radiation is not considered, traditional operating range equation of infrared search and track system(IRST) has a limit. In order to complete the equivalent calculation of operating range of IRST on small dynamic target rapidly in various meteorological and flight conditions, the operating range model on point target of IRST was derived in the sky background. Based on the equation, the operating range of one IRST on the target drone in all kinds of meteorological conditions was calculated. In addition, the equation was validated by the data of target drone flight test and it is proved that the equation is correct and can be used to the equivalent calculation of operating range of IRST. Finally,the operating range of IRST on one kind of missile under different flight and specifically meteorological conditions was calculated based on the equation.
2013, 42(1): 31-35.
Infrared radiant planar source is used to simulate certain infrared characteristic target, widely used in different infrared detection, controlling and guiding equipment's outer field test. The performance of infrared radiant planar source basically depends on its temperature field control. The structure and main parts of radiant planar source were described. Taper shape was adopted at planar surface to increase the infrared emissivity. High power heater controlled by temperature controller was used for heating. The heating power was determined by thermal analysis and calculation. The air duct was designed and suitable cooling fans were selected through CFD simulation. The experiment results show that the temperature stability and uniformity of whole radiant plane fulfill the requirement. The radiant source can be adjusted at any temperature in a range of [80 ℃,300 ℃] within 30 min. The temperature deviation is less than 1.5 ℃. The radiant source can simulate different infrared behaviors by setting different work temperature.
2013, 42(1): 36-40.
Radiometric calibration is very important for radiation characteristic measurement of the infrared system. The indirect calibration system was adopted, which was equipped with the collimator collected with the area blackbody as the extended radiant source. Firstly response model of the infrared focal plane arrays and the response characteristics related with the blackbody radiation and integration time were analyzed. Then through the least square fit method, response function of pixel respon gray value versus target radiation and integration time was demonstrated. Finally, the response function at different ambient temperature was compared with the former function, which further verified the effectiveness of the equation. This method can simplify the calibration process and save time. Besides, the calibration equation can be used to conduct quantitative analysis on impact factors of the calibration, and measure radiance in a wide dynamic range.
2013, 42(1): 41-45.
A feasible method considering the character of marine infrared image was proposed to detect objects in the sequential images from surface vehicle, which was not only appropriate for sea-sky background but also for offshore background. There was no need to filter the noise. Firstly, the complexity of sub-images and the average gray difference of their up and down neighborhood were measured to predict the sea line region. Secondly, improved Canny edge detection was applied to extract the contour of the sea line region. It made the sea line obvious and meaningless edges disappear greatly. Thirdly, Hough transformation was used to pick the longest line as the sea line. Finally, a kind of general concept of gradient was put forward. The targets could be marked excellently under the fusion of gradient. The experiment results show that this method can locate the sea-line region and the sea line with any tilt reliably and obtain the information of objects effectively. The whole procedure costs about 60 ms and it is real-time and robust.
2013, 42(1): 46-50.
The wire bonding quality of InSb infrared detector chip surface solder joint and external pin solder directly determines the reliability of the optical signal output. Ultrasonic power, bonding time and bonding force are the most important process parameters for the wire bonding quality. Based on the practical application, gold wire bonding was performed on a KS 4124 wire bonder with the gold plated pads, and the effects of these process parameters on bond shear force and the bonding region were studied. By analyzing the failure mode of bonding and the solder joints morphology, the optimum process parameters meeting InSb chip gold wire bonding quality requirements were obtained. This study has laid a solid foundation for the InSb chip wire bonding reliability.
2013, 42(1): 119-124.
Fiber optic gyroscope(FOG) is sensitive to temperature, and there is a certain temperature drift error in the working process of FOG especially in the startup phase. In this paper, to reduce the bias drift in the startup phase of FOG and shorten the startup time, a scheme based on radial basis function (RBF) neural networks was designed to compensate the drift in the startup phase of FOG. The model took the temperature of FOG and the temperature change rate as the inputs and used the bias drift of FOG as the output. In the room temperature, the RBF neural network was used to compensate the startup drift of FOG, and the experiment shows that the method can effectively reduce the temperature drift and shorten the startup time of FOG. This method is used in a certain type of FOG north finder and can greatly reduce the preparation time, and so improves the north-seeking accuracy.
Fiber coupling efficiency and Strehl ratio for space optical communication based on adaptive optics correction
2013, 42(1): 125-129.
The received laser beam in a free-space optical communication using fiber-optic components system must be coupled into a single-mode fiber. However, atmospheric turbulence degrades the fiber-coupling efficiency. Adaptive optics can reduce the effects of atmospheric turbulence and improve fiber coupling efficiency. According to space light into single-mode fiber coupling efficiency expression with the atmospheric turbulence parameters, the single-mode fiber coupling efficiency expressions based on adaptive optics correction was deduced. Simulation results show that adaptive optics system correcting the aberrations induced by turbulence can increase the spatial coherence radius and then can improve the coupling efficiency. The the relationship between Strehl ratio and coupling efficiency was studied. The results show that regardless of the presence or absence of adaptive optics correction, both have good fitting relationship. Therefore, simple Strehl ratio can be used to estimate the single-mode fiber coupling efficiency.
2013, 42(1): 130-137.
Satellite laser communication has become a hot topic of communication technology research, and the optimal design of the optical system is an important research direction of the satellite laser communication terminal. Diffractive optical elements were introduced in this paper, to realize the miniaturization, integration, high efficiency of satellite laser communication terminals. Followed by the brief introduction of the principle of laser communication system, the potential applications of diffractive elements within a laser terminal were exhibited, such as beam shaping and splitting, optical filtering, antireflective coating, aberration and thermal compensation, etc. A design example of laser terminal including diffractive elements was presented, and the consequential simulation results demonstrate the advantage compared with conventional refractive elements.
2013, 42(1): 138-142.
Stray light analysis in optical system is a key technology to ensure the system's quality. According to the definition of stray light, the sources of stray light in infrared optical system and the effect of stray light were pointed out in this paper. In view of stray light source, a structure of suppressing stray light was established. In order to reduce the internal radiation, reflective vanes were used. TracePro software was also used to build the system model and simulate analysis of the system. The results indicate that stray light is well suppressed, and the system's PST can achieve a level of 10-5-10-8. At the same time, the internal radiation energy that gets to imager can achieve a level of 10-10 W. So the system can achieve a clear image.
2013, 42(1): 143-147.
An optical system of roll-pitch infrared seeker with optical, mechanism integraled structure was presented. With the use of four reflective plane mirrors, the subassemblies of the optical system embed in the gimbal. The gimbal consisted of roll frame with N360 moving range and pitch frame with 90 moving range, so that the optical system could be adjusted to look over all of the front hemisphere field. The optical system design process was as follows: firstly, a reimaging system was set up, including front group, relay lens and rear group. As a high thermal gradient existed within the seeker, the front group must be athermal design alone, while the relay lens and rear group can be athermal design together. Then, the initial optical power distribution among lens can be resolved with the design method of mutual compensation of thermal dispersion. Finally, the optical system's aberrations were corrected by ZEMAX software. The analysis results show that when environment soaking temperature or gradient temperature varies from -40 ℃ to 80 ℃, the image preserves high quality and modulation transfer function (MTF) still approaches diffraction limit. The optical system achieves optical, structure and thermal integrated design.
2013, 42(1): 148-153.
A refractive/diffractive long wavelength infrared continuous zoom system was designed based on the new staring focal plane array (384 pixel288 pixels) in order to improve the resolution of image, detecting distance and accuracy of the infrared system and to satisfy multifarious situations. The operating wavelength of this system ranged from 8 m to 12 m, F number was 1.5 and the zoom ratio was 25:1. The binary surface was introduced to correct the lateral color and other high order aberrations and to modify the system. Moreover, detailed design and image quality were given by CODE V optical design software. When spatial frequency was 20 lp/mm, modulation transfer function (MTF) in the whole field of view exceeded 0.4', approaching diffraction limit. The final results show that this optical system has large zoom ratio, high resolution, small volume and excellent image quality. Thus, it can be applied in many kinds of optoelectronic detection fields.
2013, 42(1): 154-158.
A summary of dome protecting technologies design of high-velocity guided missiles was made in this paper. Based on a lot of US patents and other references, the classification of dome protecting design methods and analysis of the strengths and weaknesses and the scope of application of the various technologies was made. The temperature and thermal stress of the dome surface increased as the rise of the missile flight. Mach 2.5 is usually considered to be the thermal barrier boundary in aviation world. Conventional methods and materials can be used to design and manufacture aircraft when temperature is below this boundary, otherwise some measures must be taken to overcome the problem of aerodynamic heating, such as removal of a dome cover, installation of the shock wave cone, dome outline design and dome cooling technology.
2013, 42(1): 159-162.
In the experiment of the incoherent light source generating non-diffracting beams, the uniformity of the incident beams for generating high quality non-diffracting beams is significant. In this paper, incoherent white light LED was used as the light source. The propagation of light was simulated through analyzing the characteristics of LED light and design of uniform illumination was deduced in theory according to the conservation of light. Hence, the lens design method was obtained which could generate the uniform beam based on the non-imaging optics. With optical simulation software and ray tracing, it is shown that the design meets the requirement of uniformity of incident beams, and meanwhile, the rationality of design is demonstrated by the experimental result that high quality zero-order Bessel beam can be obtained with uniform distribution of beam intensity.
Free-form lens design method based on the modulation of the aspheric inner surface for uniform illumination
2013, 42(1): 163-166.
In the free-form surface construction process, the solution deviation is produced, which will lead to the poor illumination performance of the traditional free-form lens. To make the illumination performance better and increase energy efficiency, a free-form lens design method based on the modulation of the aspheric inner surface was proposed. The aspheric inner surface was used to modify the deviation of the free-form surface. With a proper aspheric inner surface, the expected illumination performance was obtained and the energy efficiency was increased. By calculating the deviation of the free-form surface, the relationship between the incident ray and the slope of the inner surface was built. Taking an LED street light as an example, by using the method, the uniformity of illumination improved from 0.66 to 0.73, and the light usage efficiency is improved from 47.3% to 63.2%.
2013, 42(1): 167-173.
To examine the effect of the non-spherical raindrops on laser transmission attenuation in atmospheric, based on the approximate ellipsoid model of raindrops and normalized raindrops size distribution, the scattering characteristics of raindrops cluster in the visible and infrared domain were calculated by ray-tracing method. The effects of raindrop size distribution and rainrate on the laser transmission attenuation were discussed. The numerical simulation results show that the scattering capabilities of raindrops cluster decrease in the order of JD, MP, Gamma and JT; the laser transmission attenuation are not only affected by the rainrate, but also affected by number density of rainfall, the more the raindrops, the stronger the laser transmission attenuation; while the effect of shape of raindrops is relative small. These results will be benefit to evaluate the effect of precipitation on laser transmission, which will promote the application of laser signal transmission, communication and wind measurement by laser.
To validate the precision of atmospheric molecular absorption and thermal radiance calculated by combined atmospheric radiative transfer(CART) code, using the accurate line-by-line atmospheric transfer model(LBLRTM) and moderate resolution atmospheric transmission(MODTRAN4.0), the atmospheric molecular absorption spectral transmittance and infrared spectral radiance calculated by these codes were comparied under clear-sky conditions. Then the horizontal path lengths, observation zenith angles and observation altitudes impacting on average atmospheric transmittance and integrated infrared radiance in several spectral bands were simulated on electro-optical engineering region. The results show that the precision of atmospheric molecular absorption calculated by CART is better than MODTRAN4.0, and calculation precision of the atmospheric thermal radiation is equivalent to MODTRAN4.0.
2013, 42(1): 181-184.
According to the special requirement of optical instrument to the uniformity of thin film thickness on infrared window, Femm42 software was adopted to analyze the potential in the vaccum of radio frequence plasma enhanced chemical vapor deposition system, by changing the height of DOME, and adding a metal ring behind the DOME, the problem of delamination on the edge of dome had solved. Taguchi experimental method was used to decrease times of experiment, at the same time, the secondary condition of effecting performance of thin film was found. The effects of the process parameters on the results of thin film thickness uniformity were analyzed. Finally, the optimal parameters had comfired. The DLC film that the uniformity is less 3% and can endure the bad environment test had successfully prepared.
2013, 42(1): 185-189.
By using GexC1-x, BP and -Si as high index material and DLC as low index material, GexC1-x/DLC, BP/DLC and -Si/DLC multilayer protective coatings were designed and coated on long wave band IR windows such as ZnS, GaAs and Ge. Optical performance, micro-hardness and resistance to marine environment of these coatings were studied through experiments. Based on the characteristics of IR window and protective coating material, the results of experiments were discussed. The results show that GexC1-x/DLC multilayer coatings have best optical transmittance and BP/DLC multilayer coatings is best to resist marine environment.
2013, 42(1): 190-194.
The damage threshold can increase 2-3 times through laser conditioning optical component using the subthreshold laser energy. In the process, it will make the optical component produce damage inevitably, if the damage does not affect the optical performance, which is acceptable in principle. In this paper, the S-on-1 LIDT of hafnia silica multilayer high reflective coatings was introduced firstly. Experimentally, the damage process of optical coatings during laser conditioning was studied. At the same time, the laser damage appearance that affected the optical capability and LIDT of coatings was analyzed. The result is, with the film system of G/(HL)11H2L/A, after laser conditioning for the HfO2/SiO2 multilayer HR coatings, the destroyed of outermost SiO2 coating can not affect its spectrum performance. Reversely, the LIDT of coatings is enhanced sharply because removing the nodula in the next HfO2 coating.
2013, 42(1): 195-199.
TeO2 is the main imaging crystal of acousto-optic tunable filter. There are chromatic aberration and drift in the crystal itself while the spectroscopic imaging. In this paper, based on the fundamental theory, the impact of TeO2 crystal optical activity to dichroism as the acousto-optic tunable filter was researched and its basic parameters were optimized. The I.C.Chang theoretical system and the P.A.Gass modified theoretical system were compared and analyzed. The results show that the two theoretical systems are quite different when the relationship of ultrasonic frequency coordination is calculated results in the infrared. Assuming that it was caused by the ignored the rotatory property of crystal of I.C.Chang theory, the design method of acousto-optic tunable filter based on P.A.Gass theory is applicable to infrared. The influence of rotatory property on the spectroradiometric property was smaller when the incident polar angle less than 30. Through comparative analysis research, incident polar angle of design should be less than 54.7 , which can maintain higher figure of merit of sound and light and a lower level of the ultrasonic frequency; in the infrared, the incident polar angle of the design should be less than 39.2 , between two frequency coordination deviation f is smaller.
2013, 42(1): 200-205.
To design high-quality optical devices, such as filters and switches, the effect of lattice constant on the transmission spectra of one-dimensional optical crystal quantum well(AB)5(CD)2(BA)5 was studied with transfer matrix method. The result shows that when the lattice constants of layer A and layer B separately increase with even times, the narrow transmission peaks at center frequency of band gap turns into wide transmission band, both sides of which are symmetrically distributed with two narrow transmission peaks of 100% transmittance; when lattice constants of layer A increases with odd times, a single transmission peak of 100% transmittance appears at the center frequency; when the lattice constants of layer B increases with odd times or that of layer D increases with integral multiple, three transmission peaks of 100% transmittance constantly turn up at the center frequency of band gap, and the three ones draw closer to the center of band gap as lattice constants of layer B and D are increasing; when lattice constant of layer D increases with integral multiple, three transmission peaks of 100% transmittance constantly present at the center frequency of band gap, besides, double-transmission-peak structure, which is closely related to the lattice constants,symmetrically appears on its two sides. Meanwhile, the transmittances of each double-transmission-peak enlarge with the integral multiple of lattice constants increasing. All these features can be applied to adjustable-channel optical filtering and switching, and can offer theoretical direction for experiment preparation.
2013, 42(1): 206-211.
A new theory for choosing the materials was put forward for the first time based on matching factors, providing a theory for choosing the materials in the process of structure designing in aeronautics and astronautics. The importance of materials choosing and material matching in the structure designing was recommended in brief. The general method of materials selected at present was recited, and the limitation of this method was indicated. The guiding principle of the matching calculating method and the standard establishment of matching formulation were put forward. The performance parameters of optical reflector material in common use of space remote sensing camera and structure material were analyzed. The weight coefficient was assigned according to the Delphi method and the hierarchical method, then the matching factor was computed depend on different weight coefficents. The material selected by the matching factor method is the same with a running space remote sensing camera. The results indicate the correctness of selection and the feasibility of the matching calculation.
The character of high dynamic star sensor's sky image and the deficiency of existing star tracking algorithm at home and abroad were presented. Aiming at these deficiencies, a new star tracking algorithm based on Kalman prediction was put forward. The model of stars' movement was set up based on the character of the star sensor's movement. The adaptive Kalman filter was used to predict the position of the reference stars. The star was matched and tracked by Star Neighborhood Approach. At the end of the article, the prediction and tracking results were presented. The experiment results indicate that the star position prediction errors are less than 5 pixels under the dynamic condition of 5()/s, and the success rate of tracking is up to 95%. The method can adapt for high dynamic star sensor and improve the success rates of tracking availably.
2013, 42(1): 218-227.
Compound axis servomechanism is an engineering realization of the two-channel control system, and is widely used in the optoelectronic tracking control, laser communication and beam control. The tracking precision and control bandwidth are greatly improved by the compound axis servomechanism. In high tracking control system, the compound axis servomechanism is an effective way to obtain the tracking precision of the microradian, even the submicroradian. In this paper, the basic theory and primarily technical problems of the compound axis servomechanism were introduced. In the control system of the compound axis servomechanism, the control bandwidth matching of main and subsystem tracking control was a prerequisite of compound axis servomechanism, and the control performance precision of compound axis servomechanism depended on the closed loop control performance of fast steering mirror. The recent development and technical improvement was analyzed, such as multiple compound axis servomechanism, pseud compound axis servomechanism, adaptive optics, feed forward control and so on in the compound axis servomechanism.
In the azimuth aiming system, the sensitive-axis direction of inertial unit is monitored usually with the help of right-angled prism. The azimuth aiming error was produced by the right-angled prism tilting, through building the mathematical model of the influence of prism tilting on the aiming accuracy, the accurate vector expression was founded, in addition, the conventional measuring way and technique were introduced, furthermore, a new detecting and calibrating method of prism tilting based on the rhombic prism was studied, and some leading causes that affecting the measuring accuracy of the system were discussed. Then, experiment platform was built based on our own rhombic-equipment. The acquired data proves that the measurement results are greatly influenced by the device level state along the direction of prism titling, the calibrated system has achieved high measuring accuracy less than 10. At the same time, this new system has obvious advantages on high measuring efficiency, and can be operated very simply and conveniently, it has a very important practical significance to improve the azimuth aiming precision.
2013, 42(1): 233-238.
In high power condition, not only the linewidth of single frequency fiber laser becomes wider greatly, but also its frequency stability becomes worse because of effects of many factors. PDH frequency stabilization technology can be applied in high-power condition with high frequency stability. To realize stable output of high power 1 064 nm single frequency fiber laser, the principle of PDH frequency stabilization technology was analyzed and a PDH optical heterodyne frequency stabilization system was established. It is found that the key of the PDH system is the detection of 100 MHz phase modulation optical heterodyne signal. Firstly, the optical signal was detected and amplified by Si detector with self-designed preamplifier circuit. Secondly, demodulation circuit was designed and the amplified signal and a reference signal were mixed together with a mixer to realize demodulation, as a result, the frequency discrimination curve was obtained. This indicates that the detection of the optical heterodyne signal has been realized.
2013, 42(1): 239-243.
In order to validate the feasibility of using open path Fourier transform infrared spectroscopy (OP-FTIR) to measure 1,3-butadiene concentration of industrial area ambient gas, the standard gas with known concentration was measured in laboratory first. Different concentration 1,3-butadiene were measured by open path FTIR measurement system which was based on Bruker IR-Cube. Combined with the absorbance information of 1,3-butadiene from QASOFT database, the measured spectrum was retrieved by the nonlinear least square algorithm(NLLS), and the OP-FTIR system was calibrated with linear fitting method. Experimental results indicate that the open path FTIR measurement system has stable performance, fast response and fine linearity. The correlation coefficient is 0.998. The detection limit of 1,3-butadiene is about 18.77 mgm-2. Experimental studies have shown that the OP-FTIR system can be used to monitor and study 1,3-butadiene in ambient gas,and the open path FTIR method can be used as a technology to detect 1,3-butadiene.
2013, 42(1): 244-250.
The signal obtained by self-guided torpedo by laser is the backscattering signal of warship wake flow and sea water, from which extracting the backscattering signal of warship wake flow is the key point of realizing the self-guided torpedo by laser. While the backscattering signal of water constantly influences the detection of backscattering optical signal of warship wake flow, and it is stronger than the needed signal, the characteristics of the two signals in time domain and frequency domain are very similar. So the separation of these two signals can not be realized with the traditional method effectively. The blind source separation and independent component analysis theory were used to process the signal obtained by laser detection system, and the experiment data was calculated by the software complied in the independent component analysis ideology. The results show that this method can extract the backscattering signal of wake flow from the original signal effectively in different condition, which can help the system judge the warship wake flow and its characteristics.
2013, 42(1): 251-255.
To solve the problem of restoration and clearness for multi-wave band images in object detection, a novel versatile restoration method was proposed, which was applicable for the restoration of multi-wave band images in object detection captured by imaging devices installed on missile, aerocraft or satellite. Some prior knolwedge was not needed in use of the proposed method about modes and models of degraded images. In this method, only some information of images was used, the minimization criterion function was constructed in regard to point spread function constrained by non-negative least square spatial smoothness, the optimization method was used to solve for the PSF, and the degraded images were restorated by non-blind image restoration method. The proposed method was verified by inputting a number of real images. The experimetal results show that the proposed method overcome some disadvantages of the exist image restoration methods such as non-versatility, good result to synthesized images, poor result to real images, time-consuming and so on. The proposed method can recover infrared, visible and millimeter-wave multi-wave band images without knowing the prior knolowdge. When inputing an image, the system output a clear image quickly. The proposed method was effective for the restoration of multi-wave band images in object detection system.
2013, 42(1): 256-261.
It is very significant to detect avian in a real time and identify them exactly. A novel approach of avian detection, imaging and identification was proposed in this paper with inverse synthetic aperture lidar(ISAIL) based on compressed sensing. The proposed approach can be stated as follows. Firstly, the optical heterodyne method and compressed sensing sampling were employed orderly to diminish sampling rate of the avian ISAIL echoes in the range. Secondly, the time-frequency analysis technique was engaged to discriminate the different moving statuses of the bird. What's more, the compressed sensing reconstruction algorithm was utilized to obtain the high resolution two-dimensional image of the bird and the fitting algorithm was used to extract the micro-Doppler feature of the bird. The avian identification and recognition can be executed based on the reconstructed high resolution two-dimensional image and the extracted micro-Doppler feature of the bird. The effectiveness of the proposed approach is validated by the simulation results.
2013, 42(1): 262-267.
Detection technology of imaging polarization has potential applications in target detection and remote sensing, with this technology the polarization state of light emitted from and/or reflected from scene can be measured. Simultaneous Imaging Polarization (SIP) is a new imaging polarization technology, which can avoid false polarization effects in time-sequential polarization detection system caused by the motion of the platform or target. The detection system can simultaneously obtain polarization intensity images of the same target among 0, 45, 90 and 135 on the same detector. Consequently, there is mis-registration among these four images, though the registration parameters are constant after the system is assembled. So, in order to obtain accurate polarization information of the detected target, registration accuracy of four images must reach 0.1 pixel. The polarization image registration method which was based on the spatial and frequency domain cross-correlation was presented. Firstly, pretreatment of these four images was prepared for image registration. Secondly, cross- correlation in spatial domain was used to achieve the pixel level of image registration. At last, cross-correlation in frequency-domain was used to achieve the sub-pixel level image registration. In order to validate the accuracy of this registration method, many experiments have been done and its registration accuracy can meet this SIP system's requirement.
Parameter estimation of noise distribution model of EMCCD based on the expectation-maximization method
2013, 42(1): 268-272.
Based on the discussion of image noise sources and their statistic characteristics of the electron multiplying CCD(EMCCD), the Poisson-Gaussian-mixture noise distribution model was established. Aiming at the problem that the solution of the maximum likelihood function of the Poisson-Gaussian-mixture distribution model was difficult to solve, the expectation-maximization method was proposed to estimate the parameters of Poisson-Gaussian-mixture noise distribution model of the EMCCD after appropriate initialization settings on the noise model, reducing the complexity of the parameter estimation and achieving equivalent effect of the maximum likelihood estimation. Monte Carlo simulation results and experimental results show that the expectation-maximization method can achieve good performance, provide satisfied fitting features for Poisson-Gaussian-mixture distribution, and obtain high precision parameter estimation values.
2013, 42(1): 273-277.
Since 1 of the 20 detectors in Terra MODIS band 5 (1.230-1.250 m) are noisy, there are sharp and repetitive stripe noise over the entire image. As for MODIS geolocated data, the stripe noise are irregular and sometimes uncontinuous, it brings a difficult problem to the image retrieving process. A detection method was presented to extract the stripe noise, and a maximum a posteriori (MAP) based algorithm was applied to correct the contaminated pixels. A local gradient based method was used to detect the abnormal pixels. In the MAP method, the likelihood probability density function (PDF) was proposed based on a linear image noise model, and a Huber-Markov model was employed as the prior PDF. The gradient descent optimization method was used to receive the destriped image. The proposed algorithm had been tested using a Terra MODIS band 5 geolocated image. The recovered images demonstrate that the proposed algorithm can remove the irregular stripes effectively. The power spectrum also shows a satisfactory result.
Line segment detection in low-SNR infrared image is difficult as the gradient field calculation is badly affected by noise. In this paper, a new approach was presented to distinguish line elements and non-line ones in an image according to the fact that gradient field phase distribution of a line area distinctly appears non-isotropic. Local non-isotropy was defined and a calculating operator was presented. By combing phase-grouping algorithm and contrario detection framework, a new line segments detection algorithm was proposed. Experimental results indicate that the algorithm can effectively detect line segments in low-SNR images with a low false alarm rate.
Terahertz (THz) spectroscopy and imaging, as the focus of THz science and technology, can be applied in many fields, such as biology, physics, chemistry, safety check, aerospace, etc. And now they are becoming international attractive field especially in recent years. Firstly, the THz time domain spectroscopy, time resolved THz spectroscopy and THz supercontinuum technology were discussed briefly. Results for characteristic identification of explosives and research on dynamics of ultra-fast charge carrier by using different THz spectroscopy were presented. Meanwhile, the THz time domain scan imaging, real time focal plane imaging, continuous wave imaging, and passive THz imaging technologies were introduced respectively. In application study, research on sunflower seeds by using THz time domain scan imaging technology, plastic cap gun covered by canvas using real time focal plane imaging technology, aerospace foam and pistol model by using continuous wave imaging technology, human body by using passive THz imaging technology were all presented correspondingly.
2013, 42(1): 57-62.
Employing nonlinear Schrodinger equations, a numerical model for nonlinear polarization rotation mode-locked fiber laser was put forward. Jones matrix was used to describe polarization controllers while two-level Giles model was used to calculate the gain. This numerical model has clear physical significance and is conducive to analyze the influence of pump power. With 1.0 m-long erbium doped fiber, 5.8 m-long single mode fiber and 85:15 output coupler, ultrashort pulse with the root-mean-square width of 0.30 ps was derived when pump power was 25 mW. The influence of pump power on the waveform and optical spectrum of mode-locked pulse was investigated, and the relation between pump power and gain distribution in erbium doped fiber was discussed. Mode-locked pulse was derived in experiment, whose optical spectrum was similar with numerical result in shape. The average power of pulse was measured and the variation trend is in line with theoretical result.
In order to study the temporal behavior of screening gray spatial solitons in biased one-photon centrosymmetric and non-centrosymmetric photorefractive crystals, the expressions of time-dependent space-charge field and dynamical evolution equation were deduced based on one-photon centrosymmetric and non-centrosymmetric photorefractive effect. The temporal behavior of the intensity profiles and the intensity full width at half maximum(FWHM) of gray solitons were studied by numerical method. The results indicate that, when the ratio between the soliton peak intensity and dark irradiance is larger, the FWHM of solitons first decreases to a minimum and then increases to a constant value; when the ratio between the soliton peak intensity and dark irradiance is smaller, the FWHM of gray solitons decreases monotonously with the increase of time toward steady state. Dynamical evolutions of the grey spatial solitons are simulated numerically at different time. Centrosymmetric and non-centrosymmetric gray solitons have the similar temporal properties.
2013, 42(1): 69-72.
In order to achieve single lateral mode of the semiconductor laser, the methad was proposed to filter high-order lateral modes by introducing photonic crystal structures on both sides of ridge semiconductor laser. By adjusting the etching depth of the laser on the surface of the laser, and ridge width and spacing of photonic crystal region,the mode field distribution inside the laser was changed, combined with selective carrier injection to enhance the fundamental mode lasing advantage, thereby the numbers of the lateral mode were reduced. 1 550 nm wavelength semiconductor lasers were produced experimentally, and the width of the main ridge was 6 m, and the period of photonic crystal region was 5 m. Test results show that when the current was 300 mA in CW, the higher-order lateral modes were suppressed, and divergence angle was reduced to 10.2. It is confirmed that it is feasible to modulate lateral modes of semiconductor laser by photonic crystal structures.
2013, 42(1): 73-78.
Based on the principle of self-organization, coherent combining of two fiber lasers in Michelson cavity was demonstrated experimentally. According to this principle, the corresponding physical phenomena and advantages of Michelson cavity were reasonably explained. Some key factors affecting output powers in Michelson cavity, such as design of collimating lens, reflectivity of output coupler, and the balance of two pump power, were discussed both in theory and experiment. It provides a theoretical basis for optimization of Michelson cavity, improvement of the final output power and suppression of the power leakage in destructive channel.
2013, 42(1): 79-83.
In the laser parameters systems of big science projects, the installation errors of the shrink- beam system were analyzed. The result shows that the defocus between the objective lens system and the eyepiece system affects the wavefront distortion error of the system most. Besides, the PV values of the wavefront aberration caused by the defocus between the objective lens system and the eyepiece system of the shrink-beam system were analyzed and a conclusion that there was a non-linear relationship between the PV values and the defocus was drawn. By the test system composed of large aperture long focal length collimator, fiber lasers and Hartmann wavefront sensors, the wavefront aberration of the laser shrink-beam system was measured and verified real-time. The result shows that by wavefront computer- aided technology, the PV values of wavefront aberration can be less than 0.2(=1.053 m).
2013, 42(1): 84-89.
Due to space and system power limitation of fuze, when laser proximity fuze is used in conventional ammunition, multiple lasers and multiple laser receivers can't be laid out. Meanwhile, system architecture is required to be as simple as possible. Therefore, the traditional layout of the beam can't be directly applied. A new rotation circumferential scanning program of large field of single-beam, was designed. Missile target encounter model was established and theoretical analysis on target acquisition rate was conducted. System error factors were discussed. The initial prototype was processed and high-speed wind tunnel experiment was done. The results show that the program can achieve reliable connection when the speed is less then 80 000 r/min, 360 large field of detection of laser proximity fuze used in conventional ammunition can be realized. Under the premise of ensuring target acquisition rate, fuze space utilization of conventional munitions and system power can be effectively reduced.
-lactam antibiotics are widely used in clinical practice, for their broad-spectrum, high efficiency and safety features. The identification and quality inspection of antibiotics are very important. Compared to other spectral methods, terahertz spectroscopy has some special advantages. In this paper, six kinds of antibiotics of clinical medication were tested using terahertz time domain spectroscopy(THz-TDS), and their terahertz absorption spectra were got. The results show that the samples have obviously different terahertz spectral characteristics even though they have similar molecular structures, which proves that the THz-TDS technology can identify small differences in molecular structure. So it can be very useful in medicament testing and analysis, which guarantees a good prospect in medicament development, production and identification. Finally, the absorption spectrum of benzylpenicillin sodium from 0.2-2.5 THz was simulated by Gaussian 03 software. Compared with the measurement results, the vibrational modes of the sample were assigned.
2013, 42(1): 96-101.
In the fine tracking systems, the amplitude and phase of the beacon light is fluctuated which is caused by the atmosphere turbulence. In order to enhance the tracking system's performance, reducing the facula's vibration induced by the atmosphere turbulence becomes the primary goal, and the fast steering mirror(FSM) is the key instrument to reach that goal. In this paper giant magnetostrictive material（GMM）was used as the offset-generating component of the FSU, which was actuated by the elasticity of the GMM, which was controlled by the magnetic field generated by the current in the coil around the GMM. This fast steering mirror was applied in the tilt correction system for atmospheric laser beam propagation, and the tilt introduced by the turbulent current was reduced by 90%, the stability and concentration of the laser facula was enhanced greatly.
Development of an optical-fiber displacement interferometer and its application in Hopkinson pressure bar experimen
2013, 42(1): 102-107.
In order to study the dynamic response of structure subjected to the detonation of explosive charges, a direction sensitive optical-fiber displacement interferometer with the reference light modulated was made up of single-mode fiber elements, acousto-optic modulator and high-bandwidth amplified photodetector based on the laser Doppler effect and the heterodyne technique. The system had the advantages of compact, high dynamic response and non-contact measurement. The code for analyzing the raw data was compiled using the STFT algorithm. The viability of this system was demonstrated by measuring the velocity of a free surface of Hopkinson bar. The maximum velocity was 36.82 m/s and the velocity waveform was compared with results performed from strain gauge and calculated based on stress wave theory. The bidirectional velocity history of surface vibration obtained on the steel cylinder explosive experiment shows the system's ability of distinguishing the motion direction.
2013, 42(1): 108-112.
Simulation characteristics of photoconductive antenna(PCA) radiation are the important basis for design and manufacture of photoconductive antenna. The method introduced the relationship between Monte-Carlo empirical-formula and updated GaAs migration-rate versus electric-field strength. The photo-generated carrier-density of 34 m-apeture GaAs dipole photoconductive antenna was computed based on Drude-Lorentz model. Combining the photo-generated carrier-density with finite difference time domain(FDTD) method, time-domain, frequency-domain and three-dimensional radiation characteristics were simulated. The frequency spectrum of the terahertz radiation ranged about 1 THz, and its amplitude peaks were at roughly 0.8 THz, which consisted well with the data obtained from terahertz time-domain spectrum system(THz-TDS). The results show the feasibility of this method, which provides a reference for design and manufacture of the high-gain, wideband THz photoconductive antenna.
2013, 42(1): 113-118.
When CCD detectors damaged by nanosecond pulsed laser, with the deepening of damage degree, the phenomena of point damage, white line damage and complete failure appear successively in the output pictures of the imaging system, and the damage thresholds exhibit a nature of probability distribution. The laser wavelength was 1 064 nm in our experiment. At first, the CCD detectors were illuminated with n-on-1 mode, three different degrees of damage behaviors were observed, and the damage mechanism was analyzed on basis of the working principle of the CCD imaging system. The damage morphology of the samples were studied with an optical microscope, and it is found that the damage initiates from the inner part of the detectors and then spreads to the micro-lens structure on the surface. Next, the irradiation mode of 1-on-1 was employed to measure the damage thresholds for the degree of point damage and system failure. The former is expressed in the way of probability distribution, and the thresholds of system failure are around 100 mJ/cm2.