2014 Vol. 43, No. 7
2014, 43(7): 2055-2060.
A double-clad fiber collimator applied in high-power lasers was proposed. Considering the 8wedge angle of C-lens and the tail of double-clad fiber in the process of production, at the same time to consider the coupling efficiency with double-clad fiber tail, the transform matrix was modeled and calculated from the general model of Gaussian-beam through a complex optical system, using the theory of matrix optics in meridian plane and sagittal plane respectively. Combined with practical applications in double-clad fiber and C-lens related parameters, the influence of the distance between fiber tail and Clens and the influence of the parameters of the C-lens on working distance and beam waist diameter of collimator were both stimulated and analyzed. The results may be to direct the design of collimator in high-energy laser system.
2014, 43(7): 2061-2065.
Laser energy coupling coefficients of surface of aluminum target were obtained by different technics, such as sandblast, roughening by sand paper and plating gold. According to classical Fourier heat conduction equation, the theoretical model for numerical simulation on temperature fields of aluminum target under intensitive laser was built up. The software based on finite element method was used to analyze temperature field distribution of aluminum target under continuous-wave (CW) laser irradiation. Temperature field distribution of aluminum target with different surface roughness was calculated, when incident laser was regular beam or Gauss beam. In authentication test, the maximum temperature rise of back surface at the center of laser beam which irradiated on surface of aluminum target was measured by thermocouple. Comparison of the numerical results with the experimental results shows the availability of the finite element method. Analyzing ablation morphology after laser irradiation, the results are coincident with the numerical simulation.
2014, 43(7): 2066-2069.
Nd:YAG/Cr4+:YAG bonding microchip laser crystal was used to develop a passively Q-switched high pulse energy narrow pulse all solid state laser. The pulse laser diode (LD) pump was used in this all solid state laser. The structure of oscillator and twice amplifications were designed. Besides, the self-excited oscillation and the restraining method were also analyzed. On the basis of stable oscillator laser output, the 1 064 nm output laser was obtained when the electric current of twice amplifications were 83 A and 85 A, respectively. The maximum single pulse output energy of the output laser was 120 mJ and the pulse width of the output laser was 1.28 ns. A green laser which the single pulse output energy was 65 mJ and the wavelength was 532 nm was obtained by the method of frequency doubling. The characters of narrow pulse and high beam quality can be used to provide a good pumping sources for the femtosecond lasers chirped pulse amplification.
2014, 43(7): 2070-2073.
Taking advantage of atom lithography to produce the nano level grating has become a mature process technology in nano fabrication. When the atoms pass through a standing wave field, using the dipole force on the atoms is a new technology to build the nanostructures. The grating obtained by this method has its special characteristic. Its period is directly related to the wavelength of laser and this can be reviewed to the transition frequency of the atom. It is hoped to use a new kind of light mask to improve the deposition quality. Using double-layer light mask have been mentioned for several times. In the experiment, geometrical optics were used to achieve what we need. A prism was designed to generate this special beam. From the experiment result, the beam is well generated. This kind of beam can be easily used in the subsequent experiment.
2014, 43(7): 2074-2080.
High repetition rate laser damage properties of optical coating have been the focus of the laser film researchers. In order to study the damage characteristics of optical coatings at high repetition rate laser irradiation, and explore the damage mechanism, in this paper, experimental study on the damage of optical thin film components at 10 kHz repetition rate DPL laser irradiation was made. The results show that modification of electric field distribution in the coatings, and reduce the peak value of electric field intensity of high refractive index material in the coatings can improve the laser damage threshold of coatings at high repetition rate laser irradiation. The damage mechanism of optical thin film components irradiated by repetition frequency laser was discussed. High repetition rate laser irradiation damage in substance is the micro-damage accumulation of amplification which caused by the combination effect of thermal effect and field effect. When the absorption rate of coatings is small, the damage is mainly caused by the micro-damage of filed effect cumulative amplification. When the absorption rate of coatings is high, that is mainly caused by the micro-damage of thermal effect cumulative amplification.
2014, 43(7): 2081-2086.
To ensure laser proximity fuze of anti-torpedo torpedo (ATT) detecting the torpedo target in rendezvous process, the minimum scanning frequency and the minimum pulse frequency that can satisfy requirement was calculated. The working principle of laser proximity fuze was studied, and the critical condition of the minimum scanning frequency and pulse frequency that make the fuze just detect the target were obtained. The rendezvous relations between ATT and target were described by three kinds of coordinate system, the computation models for the minimum scanning frequency and pulse frequency were built, and the changing rules of the minimum scanning frequency and pulse frequency were got. Through simulation test to prove the correctness of the built computation models, the test results tally was in line with the theoretical results. The minimum scanning frequency and pulse frequency that is necessary to intercept different typical torpedoes were calculated. Thus, this work can provide a theoretical basis for designing the scanning frequency and pulse frequency of laser proximity fuze.
2014, 43(7): 2087-2091.
A novel method for generating muti-Bottle beam based on the property of multimode interference in multimode fiber was proposed. The structure of single mode fiber-multi mode fiber was a multi-mode fiber (MMF) spliced onto a piece of single-mode fiber (SMF). When input field propagated to MMF, only linearly polarized (LP0,n) modes were excited. As a consequence of the superposition of multimode interference, multi-Bottle beam can be generated at certain axial regions in free space. In this paper, the theory of propagation process was analyzed and numerically simulated using Matlab software. The result indicates that the size of multi-Bottle beam about 400 m20 m can be obtained in free space. 45 m, 60 m, 90 m diameter MMF are selected, the size of Bottle beams obtained from them are almost the same, but both side relative intensity of axial region of dark space are 0.62, 0.41, 0.11 respectively. Therefore, the larger diameter of MMF, the more similar intensity is on both side of dark spot. It can work better for trapping particles.
2014, 43(7): 2092-2096.
In order to solve the problem that the high fill factor and accuracy of the refractive lens are difficult to realized, a new approach for homogenization of semiconductor laser by using diffractive micro-lens array was proposed. And diffractive micro-lens array with phase steps based on the theory of scalar diffraction was designed. The equation of intensity distribution in the focal plane was derived by the Fresnel diffraction equation. The imaging homogeneous system of diffractive micro lens array was simulated and the influences of diameter and phase steps of diffractive micro-lens on the intensity distribution were studied. The results show that the non-homogeneity about 5% and energy efficiency over 97% of the focal speck can be achieved with micro-lens diameter of 0.27 mm and phase steps of 16.
2014, 43(7): 2097-2102.
As the thermal cracks, a large amount of slag etc. exist with laser cutting on Al2O3 ceramic, a technology called low-pressure water jet and laser composite cutting on ceramics was introduced. Compared with ordinary laser cutting, the results show that low-pressure water jet and laser cutting is better, which can greatly reduce the slag and avoid thermal cracks. The influence rules of low-pressure water jet and laser composite cutting on ceramics the different auxiliary gas pressure, laser pulse energy and repeated frequency on were mainly discussed, and found out that under the water jet, the auxiliary gas pressure mainly played the role in blowing the drops away from the cutting head. When the laser pulse energy or the repeated frequency increased, the ablation of the material increased, but if the material cannot take away by the water jet, that would be accumulated to large amount of slag which will impact the quality of ceramic cutting.
2014, 43(7): 2103-2107.
Photodetector is an important part of coherent laser Doppler speedometer, and the optical intensity response of which has a great impact on the system's signal-to-noise ratio (SNR). In order to improve the detection performance, the impact of photodetector's nonlinear response on the laser Doppler speedometer was studied. The response function was deduced by using polynomial analysis. The output voltage waveform under nonlinear response was compared with that under linear response, theoretically demonstrating the impact of photodetector's nonlinear response on the SNR of the system. Comparison experiments indicate that through the suppression of the nonlinear response, the SNR raises from 16 dB to 35 dB, which results in the correction of the analysis.
2014, 43(7): 2108-2111.
The reason of photo response non-uniformity (PRNU) of image sensor's photo response was analyzed in this paper at first. It was concluded in two faces, one caused by spatial noise which based on materials, manufacture crafts and offset and another caused by temporal noise which based on its response with time drift, theses two factors influence the PRNU of image sensor's photo response gravely. To describe the affection of spatial noise and temporal noise, the model of sensor based on the hypothesis that linear of image sensor's photo response was made, and the erase non-uniformity of CCD by Least Square Methods based on this model was proposed. Experiment results show that the proposed algorithm is effective to the correction of image sensor's PRNU.
2014, 43(7): 2112-2115.
Using the THz emission from air plasma, the method of determining the initial carrier -envelope phase (CEP) of few-cycle pulses was proposed. In air plasma, the evolution of the generated THz waveform can be used to probe the variation of the CEP of propagating intense few-cycle pulses. In the intense few-cycle laser fields, the inversions position and the number of inversions of the THz waveforms was found dependent on the initial CEP regularly. The calculation based on the transient photocurrent model indicates that the number of inversions of the THz waveforms is either two or one for all the initial CEP for a range of moderate input pulses energies. Under varied input pulse energies, the value of initial CEP is 0.5 constantly when the two inversions of the THz waveforms change to one. This provides a method of measuring the initial CEP of the driving few-cycle pulses.
2014, 43(7): 2116-2119.
InAs(8ML)/GaSb(8ML) superlattice with p-i-n structure was grown on GaSb substrates by molecular beam epitaxy. IV characteristic under (NH4)2S passivation showed that the ideality factor was near 2 at lower forward bias where recombination current dominated and the factor was near 1 beyond 0.14 V where diffusion current dominated. A large number of combination centers appeared at the surface barrier region originated from the vacancy defects. Compared with (NH4)2S solution treatment, the surface leakage currents density after anode sulfide treatment decreased three orders of magnitude and the zero-bias resistance R0 was measured up to 106 ohms. The figure of merit R0A was up to 103cm-2.
2014, 43(7): 2120-2125.
Based on the modified solar model by considering the attenuation and scattering of the fog, and considering the heat transfer mechanism between fog droplets and target surface in the foggy weather and the radiation and convection heat transfer of the surface, the heat transfer model of the ground target surface in the foggy weather was founded. The influence of fog visibility and wind speed on the target temperature field was analyzed by the heat transfer model. The temperature time variation characteristics of the targets in the typical foggy weather was also analyzed. The result shows that during the appearance of the fog, the smaller the fog visibility, the lower the temperature of the target surface; the higher the wind speed, the lower the temperature of the target surface. So it's very necessary to consider the influence of the fog and wet air during the heat calculation of the ground targets.
2014, 43(7): 2126-2131.
Mid-wave infrared is an important detection band. For target detection, the band selection can better distinguish the target and the background in the condition of ensuring a sufficient number of photons. For the mid-wave infrared spectrum characteristic of the representative targets and background, the detection effect of signal-to-noise ratio (SNR) and signal-to-clutter ratio (SCR) was analysed. The band selection method based on synthetic signal-to-noise ratio (SSNR) was proposed. The sensor noise and radiation of backgroud clutter were considered synthetically in this method. The target SNR、SCR and SSNR in some representative conditions were calculated. Simulation results show that the band of high SSNR is different in the different type scenes. The advice of optimization detection band is proposed. In the condition of daytime detection, 3-3.7 m can be considered as a preferred band. In the condition of night detection, 3-5 m can be considered as a preferred band.
2014, 43(7): 2132-2137.
In order to enhance the efficiency of infrared radiation calibration, a simple calibration method was brought forward. First, the radiation calibration model comprising integral time was put forward. Through the relation between integral time and cell's response gray in company with the relation between blackbody's radiation luminance and cell's response gray, the concrete form of radiation calibration model was confirmed, and physics meaning of parameters in the formula were introduced. The radiation calibration experiments at different environmental temperature were processed and the changes of the unknown parameters with environmental temperature were plotted. The experiment results validate the radiation calibration model. A simple method for radiation calibration basing the model was brought forward, choosing two calibration points with the help of unitary linear regression method and collecting the two calibration points at two typical integral times, then the unknown parameters in the radiation calibration model were calculated through these four figures. Finally, comparison between the calibration data caught by calculating employing the model and actual calibration data caught by calibrating were took on. Experimental results indicate that the error between calculating and calibrating is small than 1%. The radiation calibration model is correct and the calibration efficiency could be boosted greatly.
2014, 43(7): 2138-2142.
When the IR imaging system observing the target, especially small target, gray resolution is not enough. In this paper, a gray super-resolution technology based on adaptive scene characteristic was proposed. The description on method of imaging super-resolution was given by adjusting the ranges of imaging signals on infrared focal plane imaging system in details. The three contents were as follows: extracting the gray characteristic of the scene, analyzing gray characteristic of scene to get the adjusting witness for super-resolution adjusting; combined with adaptive filtering algorithm based on LMS to give the adjusting parameters after filtering on adjust witness; completing gray super-resolution by controlling the parameters in super-resolution circuit. At last, the total scheme was validated with experiment. The experiment in infrared focal plane array imaging system has proved the feasibility of this method, and the imaging quality is improved evidently. Gray resolution is improved greatly. The system MRTD can be improved more than one times in the test.
2014, 43(7): 2143-2147.
The detection of point target is always an important research subject of infrared imaging system. Based on the irradiation distribution function of point target under action of point spread function, considering the positional relationship of irradiation distribution and unit detector,according to photoelectric conversion relation,the transformational relation of optical signal to electrical signal of point source detected by IRFPA was established. then, combining with detector noise model, new SNR model of point target was showed. There was a conclusion that detective point target SNR was closely related to point spread function, size of unit detector and line-of-sight displacement. This method could be a fundamental of accurate estimate of view range of infrared imaging system.
2014, 43(7): 2148-2151.
Indium bump fabrication is a key step of infrared focal plane arrays (IRFPAs) process with flip-chip bonding between sensor chip and Si readout integrated circuits (ROICs), and indium bump height is an important factor of indium bump fabrication quality. The usual method for indium bump height statistics is manual observation of the randomly picked indium bump by microscope. However, it can't comprehensively reflect the true situation for the lack of enough samples. On the other hand, the subjectivity of manual observation makes the statistical results inaccurate. In this paper, an improved method of the statistics of indium bump height was stated. First, the confocal laser scanning microscopy (CLSM) was used to scan the surface morphology of the indium bump arrays, then, MATLAB was used to work out the specific indium bump heights by analyzing the data CLSM scanned, when concerning the morphology's influence on the calculation of indium bumps. A real statistic of 1616 format ROIC was done, and the result was better than manual observation. It can provide indium height data with great accuracy for evaluating the indium fabrication quality by using this method.
2014, 43(7): 2152-2158.
In the panoramic field-of-view (FOV) infrared imaging search system (PIRSS), the infrared image background was especially complicated, along with rapidly increasing of the data quantity. According to the infrared image's characteristics in the PIRSS, a flow of detecting algorithm based on the weighted local entropy (WLE) matrix of image blocks was proposed. Firstly, it established the image blocks matrix for the entire image, which was based on the spatial distributing characteristics of the panoramic image. Then a new characteristic function called weighted local entropy was presented, and calculated the WLE matrix for the image blocks. Finally, an appropriate adaptive threshold method based on the analysis of WLE matrix was adopted, which implemented the region separation of candidate targets from background and obtained the ROI. Experimental results demonstrated that the proposed algorithm was effective and befitting for the infrared target detection in large FOV. It also has good performance for real-time processing and engineering realization.
2014, 43(7): 2159-2163.
The calculation of radiant heat flux on satellite orbit is of great significant for satellite in both the thermal design and control and research of its infrared features. In this paper, firstly combined with the six elements of satellite orbit parameters which describing satellite motion model, and with the use of the coordinate transformation method, the position relationship and angle relationship of the satellite's each surface and the sun. The earth were established. Secondly, the satellite surface radiation heat flux calculation model was established. And the major orbit radiation heat flux such as solar radiation, earth-reflection and the earth radiation of satellite with any orbit parameters and at any time can be calculate with the model. Thirdly, taking a hexahedron satellite in an orbit for instance, the radiant heat flux on its different surfaces during the period on the orbit was calculated. Results show that different surface received radiant heat flux are not the same, which mainly depend on the angle relationship of the surface and the sun and the earth.
2014, 43(7): 2164-2169.
Small-target tracking in infrared imagery with a complex background is always an important task in object tracking fields. Small and manoeuvrable objects in complex clutter and highly noised background usually results in serious false alarm in target tarking for low contrast of infrared imagery. An improved Mean-Shift algorithm to handle the influnce of complex background during tracking the smalltarget in infrared imagery was proposed. This work proposed an adaptive nonlinear machine to help Mean-Shift algorithm to get stable histogram of the interesting areas. This machine expanded the imformation of object histogram refer to the mean value of tracking window, as well as reduced the noise part of tracking window refer to the standard deviation of it. At the same time, algorithm fused the histograms of gradient with histogram of gray-value to discribe the target. To validate the effection of the proposed algorithm, the last part conduct a series tracking experiments which choose highly noised and clutered videos as their candidates. The comparison of the tracking results between tradtional Mean-Shift algotithm and improved Mean-Shift algorithm shows that the proposed algorithm has a more accurate tracking effection. Further more the proposed algorithm highly reduced the wobbleing between small-target and tracking window. This indicates that the improved algorithm achieved more robustness.
2014, 43(7): 2170-2174.
An I-V converter circuit was designed by using the infrared communication. The converter circuit contained a transimpedance amplifier and two compensation structures. The DC compensation circuit was used to compensate the DC photocurrent generated by ambient light and prevent the saturation at later stages. The AC compensation circuit was used to improve the AC input impedance and preserve the sensitivity of the signal of interest. The research shows, through the I-V conversion circuit to realize the double compensation, the gain control of the circuit and sensitivity are improved significantly. This circuit is implemented in the 0.6 m BiCMOS process. Operating under 3 V, it achieved a DC photocurrent rejection ranging from 10 nA to 300 A and the gain obtained with 110 dB with a good stability.
2014, 43(7): 2175-2179.
The reflection spectra of Aspergillus niger spores within the waveband of 2.5-15 m were measured by squash method. Based on the measured data, complex refractive index of Aspergillus niger spores within the waveband of 2.5-15 m were calculated by using Krames-Kronig (K-K) relationship. Then, the mass extinction coefficient of Aspergillus niger spores within the waveband of 2.5-15 m were obtained by utilizing Mie scattering theory, and the results were analyzed and discussed. The average mass extinction coefficient of Aspergillus niger spores is 0.68 m2/g in the range of 2.5-15 m, and the average mass extinction coefficient decreases monotonically with the particle size increases. Compared with common inorganic compounds, Aspergillus niger spores possesses a good extinction performance within the waveband of 2.5-15 m, and the requirement of particle size is relative wide in a certain extinction performance.
2014, 43(7): 2180-2184.
As the fundamental factor of high precision optical producing, the testing accuracy of interferometry is the key of producing accuracy. In order to solve the problem of large optical flat mirror testing, a kind of stitching factor was provided for overlapped area values, based on the stitching algorithm. At the meantime, the stitching measurement was completed for a 120 mm flat mirror with a 100mm interferometer. Comparing the stitching result with the full aperture testing result with a 150mm interferometer, it turns out that the stitching result is smooth and the relative deviation of PV and RMS between the stitching result and the full aperture testing result is 7.25% and 7.14% respectively. The testing result is consistent, verifying the reliability and accuracy of the stitching testing.
2014, 43(7): 2185-2191.
Drift angle is an important factor which disturbs image quality of linear array CCD camera in push broom imaging mode. In order to realize fast calculation to drift angle under limited computational resource condition on orbit, a drift angle expression applied to remote sensor with straight, forward and backward sight on circular orbit was constructed, based on character of relative motion between velocity of camera on round orbit and of ground target which moved with rotation of the earth. Mathematical expression of angular vibration of the velocity vector of satellite relative to target during satellite's flight was given. The real-time adjusting method based on CCD rotating was presented and verified by constructing imaging testbed of real-time drift compensation. Simulation and test results indicate that speed vector model has higher calculation efficiency, and calculation accuracy and stability are as much as method of coordinate transformation and orbital element. MTF degradation can be suppressed to 5% with drift compensated by speed vector model. The method can be further used for development of drift angle real time adjustment mechanism of TDICCD camera and three-line CCD 3-D photography camera.
2014, 43(7): 2192-2197.
The effects of preparative parameters such as substrate temperature, ion beam voltage, ion beam current and oxygen flow on the deposition rate of films were systematically researched by using the orthogonal experiment design method. The films including HfO2, Ta2O5 and SiO2 films were prepared by time-power monitoring of ion beam sputtering technology. The 9 groups experiments were arranged by L9 (34). The physical thicknesses of all the 27 samples were measured by elliptical polarization instrument, and then the deposition rates were obtained. The experimental results show that the deposition rate of Ta2O5 and SiO2 films are affected by preparative parameters with the same influence weight, from high to low the order is ion beam current, ion beam voltage, oxygen flow and substrate temperature. But to the HfO2 films, the order is ion beam current, ion beam voltage, substrate temperature and oxygen flow. The results provide references for adjusting the deposition rate of HfO2, Ta2O5 and SiO2 films.
2014, 43(7): 2198-2203.
A spatial angle measurement model was established based on polarizing beam splitting principle of Wollaston prism. The influence of exit light intensity from Wollaston prism on the system angle measurement accuracy was made by theoretical analysis and simulation briefly. The simulation results show that the exit light intensity deviates from the Malus'law, a certain nonlinear deviation is presented, and there is a great influence of the nonlinear deviation of Wollaston prism on the angle measurement accuracy of spatial angle measurement, the practical value of the device is reduced. Furthermor, a method of square wave magneto-optical modulation was presented to improve the angle measurement accuracy, which effectively eliminated the influence of nonlinear coefficients of Wollaston prism, fluctuations of magneto-optical glass modulation, differences of circuit gain and fluctuations of the light intensity. Finally, by doing relevant experiments, the system angle measurement accuracy can reach 15 in the range of-8to +8by using this method.
2014, 43(7): 2204-2208.
A non-destructive method was described for characterizing biological cells scattering. Firstly, the numerical simulation was performed to analyze the light scattering properties of biological cells based on the discrete dipole approximation (DDA). Then the angular dependence of the scattering intensity related to the relative refractive index, and the particle diameter were discussed in detail. The analysis shows that the scattering intensity of the living cells increases with the scattering angle and relative refractive index, and the main scattering energy is concentrated in the scattering angle less than 10. In addition, an experimental measurement on suspended bovine kidney cells was performed and the results was compared with the simulation. Finally, the angular distribution of scattering from the simulation and experiment matched well at the angle range of 5 to 52. This result demonstrates that DDA can be used for further theoretical research and experimental methods for biological cells scattering characteristics.
2014, 43(7): 2209-2213.
In order to realize the 109 times absorption for residual laser after 4% sampling, a kind of design method of light absorber was given. From light entrance to light exit the absorber, total angle relations were derived, including the angle of entrance light intersection with the absorber, turnover angle from entrance to exit, the angle of exit light intersection with the absorber, and turnover angle of the light departure from the absorber. The calculated angles were taken into polarization formula, and the sampling efficiency from every intersection was gotten, and so the total process attenuation was obtained from light entrance to light exit the absorber. According to the above formulas, a kind of absorber was designed, and it was analyzed in optical software. The results show that the absorption can reach to 1011, which satisfies the absorption requirements and is identical with theory calculation; This kind of absorber has been used in the laser system well, near field image with modulation M1.2 and contrast C0.07 are gotten, so the design method is reasonable.
2014, 43(7): 2214-2218.
To meet the requirements of high location accuracy and surface figure accuracy for space mirror set, reducing support weight extremely at the same time becomes the new important research subject in most countries. A topological optimization design for a space mirror support lightweight was presented in this paper. By using finite element analysis technique, the static stiffness of the mirror was analyzed. The analysis results show that the surface accuracy reaches /10 PV, /50 RMS (=632.8 nm) under gravity load, PV value is 13.3 nm, RMS values is 2.9 nm, the mirror component first-order natural frequency is 239 Hz, which is better than traditional structure forms of mirrors, and can meet the application requirements.
2014, 43(7): 2219-2222.
A measurement system based on scanning diffuse reflection imaging was developed for space-time distribution of laser intensity. The measurement system mainly consisted of spoke-shaped sampling structure, synchronous signal generator and CCD imaging system. Instead of the traditional static diffuse reflecting screen, sampling was realized with several spoke-shape dynamic rotating arms, which was feasible for online measurement of laser intensity distribution. Besides high resolution of the traditional method, there were more advantages in this scanning diffuse reflection imaging method, e.g.high laser attenuation ratio, strong power against laser destruction, simple structure and better maneuverability. Comparative experiments with the diffuse reflecting screen imaging method demonstrate high correspondency between the two methods. This system can be applied in the real-time monitor of laser intensity distribution in laser irradiation effect experiments.
2014, 43(7): 2223-2227.
Radar cross section(RCS) measurement is of great significance to terahertz(THz) radar system design. Firstly, the principle and experimental design of RCS measurement based on time-domain spectroscopy (TDS) system were introduced. Secondly, by using TDS system, the time-domain echo of smooth and rough cylinder were obtained. The measured RCS value can be given after Fourier transform. Compared the measured value with the physical optics solution of the same size cylinder, the results shows that calculation and measurement have the same result which prove the TDS system can be used to measure RCS in terahertz band. Finally, comparison of measured RCS value between the smooth and rough cylinder indicates that the higher frequency, the greater impact of rough surface on RCS in terahertz band, and the traditional definition of rough surfaces which roughness more than one eight of the wavelength is not suitable any more.
2014, 43(7): 2228-2233.
In the indoor pseudolite positioning system, the effects of the near-far problem always lead to the losing lock in tracking loop. To reduce the effects of the near-far problem, an effective algorithm, vector tracking loop(VTL) algorithm was proposed in this paper. The structure of the VTL was analyzed. The linear model of the system and the operation of that were shown. In the VTL, positioning errors were considered as statements, the pseudorange errors and pseudorange-rate errors were regarded as measurements. Combined with the updated positioning results, a stable tracking control input could be obtained. A simulation result was made to compare the tracking ability of the blocked signals among the scalar tracking loop (STL) and VTL. Furthermore, an independent indoor pseudolite positioning system was set up. From the experiments, the VTL system could dramatically reduce the effects of the near-far problem for STL.
2014, 43(7): 2234-2239.
Considering the practical problem that existing equipment can not complete the mission of high precision simulating stars'position and illumination uniformity of star points in the test of high precision star sensor, a type of high precision dynamic star simulator was designed. To ensure the accuracy of the projected stars, a method of LCOS optical splicing was presented. Optimization principles and image quality evaluations of the collimating optical system with large field of view were give in detail. In order to meet the lighting conditions and illumination uniformity, an illuminating optical system using fly eye lens was designed. By determining mechanical structure of the five dimensional high-resolution adjustment frame and establishing three-dimensional model of design results with CATIA, displacement resolution was achieved to 18 nm, angle resolution was achieved to 0.05. Through experimental tests, it is found that the micro-adjustment mechanism is stability, the illumination inhomogeneity is better than 10% and angular distance accuracy is less than 12. The designed simulator can approach the test requirement of high precision star sensor.
2014, 43(7): 2240-2244.
In O-E stabilization turret, the stirling cooler's disturbance and axis's friction torque are both the main disturbance. Considering the traditional control methods are insufficient to restrain the above two kinds of disturbance, Kalman filter algorithm was introduced to the photoelectric stabilized turret in this paper, its role was to use the recursive algorithm to filter the system and random measurement noise. The simulation results prove it effective. Compared with the classic PID regulator, the regulator based Kalman filter can improve the stable precision from 40% to 1%. The goals to improve the stability and to overcome the noise interference are realized.
2014, 43(7): 2245-2250.
CCD mosaic technology can effectively increase space camera's field of view and image width. CCD's performance difference will decrease space camera's image quality. In order to screen the same high-performance CCDs for wide field of view space camera, a method of CCD test and screening was proposed. Firstly, the design of CCD's imaging circuit and the test method of CCD's spectral and radiant characteristics were introduced. Then, the screening process of the CCD was introduced, the first step was screening CCD on the basis of the geometry characteristics, signal-to-noise ratio, relative spectral responsivity, photo response non-uniformity, non-uniformity, non-linearity, dark current, and dynamic range, then the poor-performance CCD would be removed. Secondly, the CCD on basis of radiant response consistency was screened. And data analysis shows consistency screening method of saturation irradiance is better than consistency screening method of responsivity. Finally, the most consistent four CCDs was screened from ten CCDs by consistency screening method of saturation irradiance, whose saturation irradiances'relative deviation was 0.23%. The screened four CCDs has been used in a wide field of view space camera, which received wonderful results.
2014, 43(7): 2251-2256.
The large collimator defocus phenomenon becomes more serious due to the substantial change in temperature and atmospheric pressure during the simulation experiments of space environment. In order to solve this problems that there is an increasing difficulty and a bad accuracy when detecting the defocus of collimator, a new method was proposed to detect the focal plane position and monitor the defocus amount in real time for large diameter long focal length collimator. The major systematic errors which induced by the pentaprism were analyzed, and they were corrected by using the method of updating the reference data. Experiments which have been performed on the collimator of 700 mm aperture and 18 m focal length showed that the detection accuracy of focal plane position can be reached 150 m, and it fully met the requirements of optical test in laboratory that position accuracy of focal plane should be less than 200 m for large collimator.
2014, 43(7): 2257-2262.
In order to meet the requirements of industry, aerospace and defense for miniature pressure sensors, an optical F-P interferometry pressure sensor which was made from all-glass material was presented, the sensor head of which was made from all-glass material. The processing steps of MEMS craft for fabrication of the all-glass optical pressure sensor were studied mainly, F-P cavity was made on 7 740 wafer based on sputtering, photolithography and etching technology, a 40 nm thick amorphous silicon layer deposited by low-pressure chemical vapor deposition (LPCVD) on this wafer was used as an intermediate layer. Then glass-to-glass anodic bonding was finished under the temperature of 380. Finally, the pressure measurement system was established. The experiment result shows that a high repeatability in the range of 0-400 kPa pressure and a reasonable sensitivity of 1.764 nm/kPa have been obtained in this pressure sensor. The temperature-sensitivity coefficient of the sensor was about 0.15 nm/℃ in the range of 0-80℃. The study of the pressure sensor would be of utility value for design and fabrication of low temperature drift typed pressure sensor.
2014, 43(7): 2263-2269.
Based on the real-time applications of EMCCD imaging system in low light environments, for the characters of output signal and the strict requirements of the EMCCD drive signals on phase, frequency and amplitude, a strategy after in-depth analysis about functions of each part of the analog front-end (AFE) was proposesd to improve the the EMCCD driver circuits, optimize the drive signals quality and reduce the noise level of EMCCD AFE. A real-time, low noise, stable EMCCD camera was designed, which can work in low light level situation. Testified by projects, when the ambient illumination is 1 10-3 lx, EMCCD camera has real-time and high-speed imaging capability, when the signal clock is 12.5 MHz, the image data rate is 25 frames per second, the output signal is stable and low noise, the captured images are clear, stable, basically meets the real-time applications requirements for the EMCCD imaging system in low light environments.
2014, 43(7): 2270-2276.
To improve the time synchronization precision of ultraviolet limb imaging spectrometer, the algorithm of clock drift rate calculation which was based on reference clock source was put forward. Firstly, the principle of limb time system was analyzed, then by using time tag unit of 1553B interface chip as clock reference source, the continual sample data was obtained and clock drift rate based on linear fit was calculated. Lastly, dynamic compensation of clock drift rate and optimization of limb system were realized. With using GPS time synchronization system, time synchronization system of high speed FPGA chip was designed, therefore dynamic changes of limb time synchronization errors were recorded by simulation and test equipment, furthermore limb time synchronization errors were measured dynamically. Time synchronization precision was measured. Experimental results indicate that time synchronization errors are no more than 13 ms for imaging beginning time error, the imaging finish time errors no more than 466.8 ms in different imaging time and no more than 362.5 ms in different integration time, which meets the demand of no more than 512 ms of qualification.
2014, 43(7): 2277-2282.
Conical and pyramidal emitters are two generic field-emitter structures. Due to specific advantages of field emission, both emitters are widely employed to produce electron beams. The main focus of this paper is to analyze the electrical characteristics of both emitters, and further, to highlight the key criteria in optimizing the structures. For this purpose, three-dimensional models were implemented and finite-element analysis was used to investigate the influences of emitter geometries, including shape of emitter, emitter radius of curvature, emitter-anode distance and emitter height, on its electric field distribution and strength. The results indicate that reducing tip radius of curvature and shorting the emitter-anode distance are effective ways to increase the field strength enhancement, while a proper ratio of the emitter height to the emitter-anode distance is also an important factor. In addition, in consideration of both electric field distribution and strength, the conical emitter is suitable for high-resolution, large current-density applications, whereas the pyramidal emitter has better pressure sensitivity.
2014, 43(7): 2283-2288.
Interpolating two-channel orthogonal fine code signals is usually applied in the photoelectric encoders to get high resolving ability, and to better perfect the interpolation technique, special research was carried out on two interpolation methods which were based on triangular waveforms and sine-cosine waveforms. Analysis was implemented separately on ideal signals where several typical errors existed, including direct current drift, amplitude error, fundamental phase error and higher harmonic error, and anti-interference ability was compared between the two different waveform interpolation methods. The photoelectric encoder with fine code signal between sine-cosine waveform and triangular waveform was tested, and for the same encoder, the accuracy was 36 when interpolated with sine-cosine waveforms, and 42 with triangular waveforms. Results demonstrate that, the anti-interference ability of interpolation method based on sine-cosine waveforms is better than that based on triangular waveforms. When developing and manufacturing high-accuracy photoelectric encoders, it is suggested that sine-cosine waveforms should be used in the interpolation of fine code signal, or launch interpolation till the actual signal is calibrated to standard sine-cosine waveforms.
2014, 43(7): 2289-2294.
For further study of the gain compensation of plasmonic waveguide for the propagation loss in the range of ultraviolet wavelengths, the metal-semiconductor-metal(MSM) plasmonic waveguide structure embedded with semiconductor gain medium was proposed and designed in this article. Based on the finite difference time-domain(FDTD) method, the dependences of propagation loss and effective refractive index on the geometrical parameters of the waveguide structure were analyzed. In addition, the condition for lossless propagation in using II-VI semiconductor material ZnO as the gain medium was investigated. The simulation results show that the lossless gain-assisted surface plasmon polartions propagation in MSM can be achieved for ultraviolet wavelengths when the width of the semiconductor core is 80 nm; and the propagation loss is much less than the gain obviously as the width of ZnO is greater than 80 nm. This achievement can realize the propagation amplification of surface plasmonic polartions, which provides the theoretical support for surface plasmon polariton nano-laser technologies.
2014, 43(7): 2295-2299.
Laser communication equipment, with large communication capacity and high-speed transmission, designed for advanced optical communication, has broad application prospects. Owing to ensure communication quality, high temperature stability and equality are required, and outside satellite parts are running in two dimensions to obtain signals in a wider range, bring challenge to thermal control. The design project was based on work characteristic of the equipment and the rule of outer space thermal environment, and a way to thermal control was proposed. Passive method and active method were carried for thermal design, and thermal design of running units, large power units cooling, radiators design, and precision temperature control design, four aspects were presented. According to the state of thermal design, a thermal balance experiment was investigated under low and hot cases, and the results prove the thermal design correct, and bring a way to thermal control for the equipment with high heat flux and running parts.
2014, 43(7): 2300-2306.
The earth background radiation and its suppression technologies for satellite-ground laser communication system were studied. Firstly, a theoretical formula of the power of entrance pupil caused by earth background radiation at different orbits was derived, and the concept of inherent stray radiation was put forward and theoretically deduced. Furthermore, theoretical calculations of earth background radiation for a typical terminal were accomplished, and baffle system designs of different forms were given. Finally, optical simulation software LightTools was used to simulate the stray radiation of the terminal with different forms of baffle system at different orbits, and then the curves of stray radiation affected by orbit altitude and the form of baffle system were obtained and analyzed. This article provides a theoretical foundation of earth background radiation for the satellite-ground laser communication and a simulation basis for baffle system of the laser communication terminal on the satellite.
2014, 43(7): 2307-2311.
Considering the narrow range and low sensitivity of recent chromatic dispersion (CD) monitoring by the asynchronous amplitude histogram (AAH) method, a novel CD monitoring technique based on asynchronous amplitude sampling(AAS) for higher order modulation formats was proposed. The parameter G, which can separate the CD from the other impairments effectively was defined. The monitoring system for 200 Gbps DP-16QAM was constructed by simulation software OptiSystem9.0. Under different optical signal-to-noise ratio and duty cycles, the dispersion monitoring was realized. The deviations caused by OSNR and varied duty cycles were investigated, and the inaccuracy was analyzed. Simulation results show that the method based on parameter G possesses the advantages of lower influence of noise and higher precision, which leads to effective monitoring of the dispersion within 0-600 ps/nm. And this method can provide a reference for the monitoring and management of dispersion in optical fiber communication system with higher order modulation signals.
2014, 43(7): 2312-2317.
In the free-space optical communication system, the acquisition technology of opto-electronic target for terminal platform is a key technology to establish a communication link. However, conventional scan method usually leads to low capture probability and the long time consumption, and count against the establishment of the communication link. So the GPS technology was adopted to complete the rapid acquisition, with the level and pitch reference sensor, and GSM network for wireless transmission was adopted. Finally, some acquisition experiments were done. The experimental results showed that the acquisition probability is 100% for fixed-point acquisition. For the simulated target acquisition, the increase of simulation speed could result in the increase of average time and the decrease of capture probability with minimum value of 60%; and the requirement for the link establishment can be satisfied for low-speed acquisition of the locomotive object.
2014, 43(7): 2318-2323.
Because of the limit of the sensitivity of detector, the relative gray scale of radar image and night viewing image is usually very low. So it is necessary to improve the relative gray scale of radar image and night viewing image. An adaptive image enhancement algorithm was proposed based on FSFLA algorithm (A Fast Shuffled Frog Leaping Algorithm). This algorithm was based on FSFLA with larger scan scope, faster convergence rate and shorter computing time. When the algorithm was applied to low light level image, the effect of image enhancement was faster to achieve compared with traditional SFLA algorithm (Shuffled Frog Leaping Algorithm). As a result, this algorithm was more applicable in actual occasion. Under the condition of twenty four given initial value, traditional SFLA algorithm needs to converge twenty times to achieve stability in average while FSFLA algorithm only needs six times in average, thus greatly improving the computing time.
2014, 43(7): 2324-2334.
The main challenges for free-space terahertz (THz) imaging are known to be atmospheric loss, moisture absorption, low radiation power; and concequently, low signal-to-noise ratio (SNR). The need to have higher power radiation sources; faster data acquisition times remain major obstacles for high image quality. In this paper, the current state of research and applications was analyzed, as well as the future development of THz imaging technology was predicted. The basic principle of synthetic aperture radar (SAR) imaging and THz compressed sensing (CS) imaging was expounded. The THz image features of the two imaging methods were analyzed. The denoising effects of THz simulation images among the Wiener2, ddencmp, Donoho and the wavelet coefficients Amplitude Asymptotically Optimal (AAO) algorithm were also compared, qualitatively. A Markov random field(MRF) model for THz image denoising was presented, in order to capture the characteristics of scale space, with better scale wavelet coefficients in the wavelet domain. The image's MRF model was established and the energy functions which were used for image denoising and the two states of each wavelet coefficient were introduced, in non-stationary regions: one state corresponded to the image features such as edge, while another state was related to the stationary region image. The Expectation Maximization (EM) algorithm was used to estimate the parameters of the mixture model, along with the Bayes Preliminary rule to determine the ideal image wavelet coefficients contraction factor. The denoising algorithm of the Hidden Markov Models in Wavelet Domain (HMMWD) was tested, with excellent simulation results that show the WDHMM to be more effective.
2014, 43(7): 2335-2340.
The traditional PCA image fusion can produce multi-spectral image information variable loss in remote image fusion. Aim to it, a new algorithm of remote sensing image fusion based on PCA and wavelet transform was proposed in this paper. Firstly, principal component transformation for multi -spectral image was performed by eigenvalues and eigenvectors in each wave band. Secondly, the first non principal component of non-gray image and multi spectral image were matched in histogram information. Finally, inverse PCA transform was carried out for three principal components to obtain the desired fusion image. Experimental results show the proposed algorithm does not only maintain multi spectral information but also enhanced the processed image details, and the processed image has better subjective visual effect and objective quantitative indicators.
2014, 43(7): 2341-2348.
A contextual hidden Markov model (CHMM) for image denoising application was presented in sharp frequency localized Contourlet transform (SFLCT) domain. Firstly, cycle spinning technology was employed on the noisy image, and then decomposed by the SFLCT into sub-images, solving one drawback of the original Contourlet transform that its basis images were not localized in the frequency domain and compensating for the lack of translation invariance property of SFLCT, suppressing the pseudo-Gibbs phenomena around singularities of images. Secondly, a new context design scheme was proposed, CHMM was established aiming at high frequency subband coefficients and applied to image denoising. Finally, the denoised image was reconstructed by inverse SFLCT and inverse cycle spinning operation. Valid transform mechanism and a comprehensive statistical correlative model that was constructed by integrating context information with HMM were utilized, which could fully express persistence across scales, directional selectivity within scales and energy concentration in the space neighborhood of Contourlet coefficients, consequently, the proposed method was more effective and suitable for image denoising. Some experiments are conducted to verify the method is more potential and certainly superior to wavelet transform method and the original Contourlet transform method, both in subjective evaluation and numerical guidelines.
2014, 43(7): 2349-2353.
The fusion of infrared (IR) and low-level-light (LLL) image offers observers more image information, but it also covers up some target information because of too much background details. To match abundant background information with target enhancement, a kind of imaging fusion algorithm was proposed in the paper. It improved the algorithm on top-hat transformation to enlarge the target information of infrared image, and meanwhile removed some redundant background details. Considering eyes'sensitivity to color, it mapped LLL and IR image into color space with color mapping formula, and then fused. The result shows this algorithm not only enriches background details, but also enhances the important target information.
2014, 43(7): 2354-2361.
The object tracking servo system requires a low delay from an object moving to starting of rotations while the inherent computational complexity of PF (Particle Filter) affects the tracking precision. In this paper, a multicore DSP parallel implementation strategy for particle filter object tracking was proposed. Firstly, the PA module on chip was used to reduce the GigE image capturing delay and the CPU occupancy. The CPU load was considerably reduced from 31% to 10%. Secondly, by manually FLUSH after writing and INVALID before reading, the memory consistency problem was addressed and cacheable shared image data can be accessed at high efficiency. Finally, a mechanism of parallel computing on multi-core processor was introduced by adding proxy task. The computational intensive stages of particle filter were dispatched to 8 cores to eliminate system delay. Experimental results show that the tracking response time was decreased and algorithmic speedup runs up to 7 and exceeds OpenMP.
2014, 43(7): 2362-2370.
Aiming at the problem that the traditional tracking algorithm has large amount of calculation and low accuracy while tracking near space hypersonic target, a kind of variable structure multiple model tracking algorithm was proposed. Established a kind of variable probability and variable model number target model on the basis of analyzing the traditional tracking algorithm, identified the target flight phase with the target motion state identification method, and selected the appropriate filter model and the model transition probability to realize variable structure multiple model tracking. The Monte Carlo simulation results show that, the new algorithm can realize tracking the near space hypersonic vehicle effectively, and the tracking performances are superior to the traditional variable structure multiple model tracking algorithm, it has certain practicability and popularization.
2014, 43(7): 2371-2378.
To overcome the deficiency that the fixed filter with single-scale cannot effectively remove the clutter and improve the performance of dim target detection, a dim target detection method based on a multi-scale adaptive sparse dictionary was proposed in this paper. Firstly, an adaptive multi-scale sparse dictionary was learned based on the sparse coding theory, and the sparse coefficient of the original image at different scales was decomposed. Then exponential fitting function was adopted to fit the statistical sparse representation coefficient histogram at the small-scale atom. Finally, the differences in the exponential fitting function for the target and noise in the multi-scale adaptive sparse dictionary could be extracted and applied to detect the target. This sparse dictionary contained the atoms with different scale, the large-scale atom can describe the background of the image, and the small-scale atom can capture the subtle feature. The results show that this proposed method based multi-scale adaptive sparse dictionary could suppress the clutter more greatly and improve the performance of dim target detection more effectively compared to wavelet and Contourlet method.
Focusing on the tracking problem of multi-target hidden in AEW (airborne early warning) radar DBZ(Doppler blind zone), a collaborative tracking technique between AEW and ground-based radar was proposed based on IMM, distributed UKF and JPDA. The dynamic fusion weights were calculated for all radars and the Doppler frequency of each target was predicted in real time using target state estimation and prediction. On one hand, as long as the target measurements of AEW radar did not exist and the target was hidden in DBZ of AEW radar judged from its predicted Doppler frequency, targets state would be extrapolated by AEW radar, which creates virtual measurements. The target fusion state estimation would be updated by both virtual measurements of AEW radar and real measurements of ground-based radar. On the other hand, when the targets measurement of AEW radar did not exist and the target was not hidden in DBZ of AEW radar judged from its predicted Doppler frequency, the targets fusion state will be updated by ground-based radar all alone. After the target fly off the DBZ, the target state estimation of AEW radar will be associated with that of ground-based radar again. And the targets fusion state will be updated by both AEW radar and ground-based radar according to the dynamic weights. Simulation results show that the presented method can improve the continuity and accuracy of multi-target tracking in DBZ.
2014, 43(7): 2387-2392.
Matching for high resolution image pairs with different viewpoints and distortions is a difficult work in remote sensing, photographing and computer vision etc. Robust Affine-Invariant Isomerous Pyramid Feature and Multi-Description for Point Feature Matching algorithm was proposed. Isomerous image pyramid was constructed by sinc convolution function series, the sinc convoluted gradient, the main direction and the strength of changes were devised for determining the normalized affine-invariant area around the key point, and the rotation-invariant projective accumulated amount and the weighted histograms were given for describing the multi-changes from the isomerous image pyramid at a special position and scale, and then, the matching was implemented based on the distribution parameters and reliability calculated by the distinctive corresponding points with big scale. Experiments show that, the new algorithm is robust for scale change, rotation, noisy, a certain degree of viewpoint difference and distortion, and the match scores are better than the state of the art matching algorithms.
2014, 43(7): 2393-2397.
near-infrared hyperspectral imaging technique was investigated for non-destructive determination of moisture content in gherkin. Multiplicative scatter correction and Savitzky-Golay smoothing were used to acquire the best pretreatment method in the spectral region between 900 nm and 1 700 nm. Optimal wavelengths were selected by regression coefficients of partial least-squares models. Prediction models were developed based on partial least squares method in the full wavelengths and optimal wavelengths. The results show that the best predictions are obtained with Savitzky-Golay smoothing spectral. Models of optimal wavelengths are better than models of full wavelengths for predicting the moisture content in gherkin, and the correlation coefficient and root mean square error of calibration and validation models are 0.86, 0.90 and 0.111, 0.156, respectively. Therefore, it's feasible to determinate the moisture content of gherkin using hyperspectral imaging technique.
