2013 Vol. 42, No. 3
2013, 42(3): 549-555.
In order to study infrared radiation distribution along aeroengine and infrared characteristic of plume, the infrared radiation characteristic of an aeroengine was experimentally studied under the condition of ground engine testing. The experimental results show that the change of infrared characteristic along engine is small under different Mach number. The temperature of low compressor outlet increases with the Mach number. And the infrared radiation of engine's ektexine increases. The most intense infrared radiation is measured in the ektexine of blending box. Ektexine's radiation of blending box changes with non-linear feature and the increasing of the Mach number. The infrared radiation of plume is pyriform. The infrared radiation after engine is bigger than that before engine. Under the condition of ground engine testing, calculation program of infrared radiation for plume is presented. The computed results of directional radiance have tallied in general with the experimental results. Relative error between computed results and experimental results is not more than 15%. The spatial distribution of computed results is similar to experimental results.
2013, 42(3): 556-561.
The temperature distribution of space objects can reflect in-orbit state. Ground-based and long-focal length imaging of space objects in infrared band provides information from which temperature distribution maps can be determined. The methods of the traditional temperature estimation are often single-band radiance and dual-band color thermometry. Uncertainties in the imaging process will reduce the traditional single-band radiance and dual-band color thermometry forward calculation accuracy. Such uncertainties include target emissivity, atmospheric transmittance, the earth's heat radiation, etc. In this paper, multi-band Bayesian estimation function model relating the measured number of electrons was established, the true temperature of space target could be more accurately solved. The model provided an estimation theoretic framework for developing optimal estimators and calculating Cramer-Rao lower bounds. The Cramer-Rao bounds of target parameter estimation function was derived, which could predict the accuracy of solving of the temperature and emissivity. Finally, the simulation and analysis of the algorithm was performed.
2013, 42(3): 562-568.
Radiation from shock layer near a window of an IR imaging detection system carried by an endo-atmospheric high-speed flying vehicle can degrade detection performance of the system. Single Line Group Model (SLG Model) was selected to describe radiation characteristic of the shock layer. Because the shock layer radiation was near field radiation to the imaging system, a relevant physical model was constructed to calculate photon irradiances caused by the shock layer radiation in the detector array. Absorption characteristic of the shock layer to target radiation was also calculated. Calculation results show that background radiation caused by the shock layer radiation in the detector array is nearly uniform and the target radiation absorbed by the shock layer can be neglectable. The magnitude of the shock layer radiation varies greatly with wavelength. In the imaging system, respective selection of different optical bandpass filters can change position of the working wave band of the system without changing wavelength width of the working wave band. According to the characteristics of the shock layer radiation, the change of the working wave band can mitigate the shock layer radiation effect on target detection and improve signal-to-noise ratio of target detection.
2013, 42(3): 569-573.
The infrared radiation characteristic is an important basis for detection and identification of dim target. The acquisition of the infrared radiation characteristic of dim target needs to utilize the large diameter calibrated equipment. Spatial filter IR spectrometer can be utilized in the observation of dim target. A radiant calibration method was studied in this paper which could be applied in large diameter IR spectrometer calibration system. With this method, the radiant existance of channels around the aperture of the spectrometer measuring system was calculated according to the standard multispectral infrared radiation supplied by the combination of blackbody and collimator tube, and it was applied into the calibration of long, short and medium wave infrared. The calibration curve was fitted with the least square method and the actual calibration result was presented. The origin and combined result of calibration uncertainty was analyzed, the combined calibration uncertainty was below 10%, which met the calibration requirement of large diameter spectrometers.
2013, 42(3): 574-578.
An improved nonuniformity correction (NUC) algorithm combining image matching and neural network(NN) for infrared focal plane array sensors was presented. Firstly, nonuniformity of the FPA response was removed by NUC compensation. Then, motion parameters of the image were estimated by matching pairs of image frames. Finally, coefficients were adaptively updated according to bidirectional-renew strategy based on neural network. Image matching technique could effectively avoid faintness when coefficients were updating. Additionally, the bidirectional-renew strategy was used to guarantee coefficients of each pixel be calculated at least once when new image frame came. The new algorithm used image matching technique to get scene motion information, and used neural network for coefficients bidirectional-renew strategy. It had a lower statistical overhead on scenes and approached convergence more quickly than the often used neural network based NUC algorithms. A theoretical analysis was performed on a collection of infrared image frames to study the accuracy of the new NUC algorithm. It proves that it has higher-quality correction ability than simple neural network based NUC algorithm.
2013, 42(3): 579-583.
An infrared measurement system was designed for relative position determination of inner-formation gravity satellite (IFGS), which was a new kind of spacecraft system to measure the Earth's gravity field. The process of determining the relative position between the moving inner-satellite and its cavity should be highly precise and without any non-gravitational disturbing forces such as light pressure, electromagnetic radiation and so on. The above requirement was handled through some novel designs which were based on the idea of thermal-electronic-mechanical integration technology. These designs include as follows: cavity configuration and cameras arrangement, layout of imaging circuits, a dynamic loop and stable thermal environment, a novel calibration equipment with delta mechanism and a suitable strategy of cross location. Though the above designs, experimental results show that infrared images with good signal noise ratio can be acquired, which are sufficient to determinate the accurate position of the inner-satellite via some smart image process algorithms. The integrated technology described in the paper provides a long-time precise measurement with the premise that disturbing forces be restrained.
2013, 42(3): 584-589.
The working principle of an extended infrared optical system was introduced in this paper. Because the imaging is usually affected by the deviation of view field due to the assembly error of wedge lens after initialization of system, a new infrared imaging optical measuring method was put forward in order to check the deviation of view field in optical system. The method integrated infrared imaging system and the computer vision technology that was applied in measuring the trajectory of motion target. The infrared imaging system was used to image the motion targets. Then the trajectories of motion target were regarded as the sequence of discrete points. The computer vision technology was used to detect the trajectories of the points and collect the image of discrete points in the continuous motion of those targets. Later, the deviation of view field of extended infrared optical system was revised by image processing of the original image of the trajectory of motion target and simulation of actual trajectory of motion target using programming. The results show that the infrared imaging measuring system which is based on computer vision technology can efficiently complete the measuring of the trajectory of motion target.
2013, 42(3): 590-594.
In the high sensitive infrared optical systems, the self-generated thermal radiation is one of the important factors for the detective property. Particulate contaminants are usually the main source of stray radiation. Besides the surface contaminants, there may be particulates within the detector. The influence on the luminous flux distribution on the image plane of the particulates inside the detector was studied in this paper. According to image plane's luminous flux distribution of the particulates inside detector with different temperature from different distance to image plane, relevant theoretical model was built up based on theory of infrared radiation and scattering, which was validated by the corresponding experiments. The results indicate that if there are particulates inside the detector used at the condition of vibration environment, they will form exception image such as black spot and white spot and combination with each other on the image plane. These abnormal distributions of luminous flux disturb the infrared targets in the effective field of view, resulting in false judgments. Thus, the veracity of the identification for infrared targets degraded obviously. Therefore it is of critical importance to keep the inside of the detector clean and prevent the generation of the particulates.
2013, 42(3): 648-652.
By use of an infrared all-sky camera, the distribution and thermal information of cloud in the sky can be obtained, thus the weather conditions can be further estimated and predicted. with the equidistance projection imaging method, every point in an all -sky image can be mapped into its corresponding spatial angle via simple data processing and conversion. An easy-to-use numerical method was proposed to acquire the profile of a catadioptric mirror, which brought the property of equidistance projection and played the most important role in a catadioptric panoramic lens. With this numerical method, an f-theta catadioptric infrared panoramic sky lens operating at 8-12 m was designed for cloud observation. The sky lens had a wide field of view of 360(5~80), the calibrated distortion was less than 0.02%, and the MTF was over 0.4 at the Nyquist frequency of 14 lp/mm. The designed camera was very suitable for all-sky observation.
2013, 42(3): 653-657.
Based on the vector wavefront aber ration theory, the misalignment induced aberration's characteristic of TMA optical system was analyses in this paper. It is shown that a misaligned TMA has three residual 3rd aberrations. The 3rd order spherical aberration that is constant over the field and the 3rd order coma is a constant in magnitude and orientation over the field. Moreover, the 3rd order astigmatism is field-asymmetric in orientation and increases linearly with the field, and the location zero for the field-asymmetric, field linear astigmatism always reside at the center of the field of view. It has been demonstrated that a TMA under assembly is only measured to have perfect performance on-axis which is not aligned in any significant way, so the measurements of multiple field points for the TMA are required in the process of alignment. Under condition of remove axial coma, if astigmatism is measured on-axis, which is caused by the primary mirror astigmatic figure error but not the misalignment.
2013, 42(3): 658-662.
Based on the extended Huygens-Fresnel integral, the cross-spectral density and Rytov's phase structure function, average intensity was derived by a formula for the Fourier transform of Gaussian function. Then mean squared root beam width, beam wander of a partially coherent Gaussian-Schell-model (GSM) beam in turbulent atmosphere were found out. It shows that beam spread and beam wander have relation with initial beam radius, initial coherence width, wavelength and transmitter hight in the atmospheric turbulence. At last, some measures were brought to decrease the effect of atmospheric turbulence.
2013, 42(3): 663-668.
For the continuous zoom system with large zoom range, a design method named double twogroup zoom system was introduced and the correspondent formulas were derived in this paper. Then a MWIR continuous zoom system with zoom range of 40 was designed. The system consisted of 8 elements with 4 aspheric surfaces, and worked in the wave band of 3.7-4.8 m. It performed with 100% cold shield efficiency in the continuous zoom range of 10-400 mm. The F/number was 4 and the zoom paths were smooth. The MTF value in Nyquist limit (16 lp/mm) was more than 0.3 and the RMS radius of the spot diagram was less than 22 m over the full zoom range. The system is of high image quality and compact in structure.
2013, 42(3): 669-674.
In order to achieve a large field of view for a 1.23m large telescope, a near-IR telescope was designed and assembled in this paper. Firstly, an on-axis reflected system was designed based on the optical theory. Secondly, by designing and analyzing the deformation of different support structures for the secondary mirror and the deformation of cylinder type and truss structure, the three-beam secondary mirror support structure and the truss structure were chosen. Finally, the assembly and adjustment was done by a proper secondary mirror adjusting structure and a proper CCD counter-rail. A test was done after the assembly and adjustment, with the result of RMS=0.106 18, PV=0.553 62(=632 nm). It is proved that the design of the near-IR system meets the requirements of the optical design and imaging according to the test result.
2013, 42(3): 675-679.
A large plane array, high resolution and small volume multi-spectral imaging optical system was designed based on the application of the liquid crystal tunable filter (LCTF). The LCTF has advantage of high spatial resolution, high spectral resolution, flexible wavelength and short tuning time. Using LCTF, a multi-spectral image whose size was about 210 mm148 mm with resolution of 350 ppi could be realized. The spectral range of this multi-spectral imaging system was from 420 nm to 720 nm and the spectral resolution of which was 10nm. The results show that when the spatial resolution is 91lp/mm, the on-axis 0 field and off-axis 1.0 field MTF at 31 wavebands are not less than 0.30, and the distortion of TFOV is less than 0.1%. Therefore, this system has good imaging quality and can be used to acquire and analyze the large plane array and high resolution spectral image.
2013, 42(3): 680-685.
As the supplement for the current computer aided alignment method for the advanced optical system, surrogate model was proposed to represent the intricate relationship between the misalignment parameters and the aberration coefficients, so a new solution method of the misalignments could be carried out. At the beginning, the principle of the sensitivity matrix method was analyzed to show its limitation, and then the surrogate model was introduced as a new tool. Comparison of various surrogate models, the artificial neural network was chosen to represent the obscure relationship between the misalignment parameters and the wavefront error, while these data were collected by Monte Carol simulation in Zemax. In the end, an off axis three mirrors astigmatism system was taken as an example to illustrate the process of building the surrogate model and calculating the misalignment. All above procedures show the practicability and reliability of the surrogate method for the optical alignment, and it is more robust and quick than the conventional sensitivity matrix method.
2013, 42(3): 686-691.
In order to advance tight integrated navigation precision and stability of fiber optic gyroscope (FOG) strap-down inertial navigation system(SINS) and globe navigation satellite system(GNSS), a SINS/ GNSS tight integrated navigation system was designed based on pseudo range and pseudo range rate. For the white Gaussian noise of FOG and instability of error statistics and model, the residual error was calculated in the evaluation of error variance matrix, an improved adaptive Kalman filtering method was proposed. Optimal estimation of navigation parameters were obtained with the improved adaptive Kalman filtering method, and system was corrected with feedback compensation. Then the divergence of Kalman filtering was well restrained and the stability of the system was enhanced. Through the static test, the results demonstrate that the designed fiber optic gyroscope SINS/GNSS system has good robustness. Under the condition of three navigation satellites, system could maintain nice navigation accuracy that verifies the excellence of tight integrated navigation.
2013, 42(3): 692-698.
The optimal augmented proportion al navigation for a constant maneuver target was deduced using optimal control theory based on the cost function weighted by a power of time-to-go. The analysis of the exponential of the weighted function shows that there exists a bijection between the navigation ratio and the exponential which gives a reasonable theoretical explanation for the engineering value of the APN navigation ratio. The seeker heading error and a constant maneuver target was introduced into the augmented proportional navigation guidance system while the guidance dynamics was simplified as a single lag. According to the mathematic thought of the adjoint method, the miss distance of the APN guidance system with a single-lag was studied and the closed-form solutions of which were deduced when the heading error and the constant maneuver target enters into the system and the miss distance closed-form solutions was validated through the simulation of the adjoint guidance system.
2013, 42(3): 699-702.
As the systematic error of the optoelectronic theodolite, the orientation error of the azimuth shafting encoder can be numbered and corrected before measuring. But the orientation error, as the systematic error, can constantly vary randomly in the course of work and inevitably make great influence on the measuring accuracy. It is believed that the gap between the joint lever and the switch port, when the leveling gear and the foundation bed are attached to each other, is the cause of error varying. On the basis of analyzing the previous solutions, the mechanical construction model combining the leveling gear and anti-twisting thin film was proposed, and it was found out that within the range of angle 7', both the bending stress and shearing stress of anti-twisting thin film were admissible stresses between the internal circle and the external circle of the anti-twisting thin film. The corner was smaller than 1of the encoder in precision. Thus the problem of azimuth axis angular adjustment was solved and it was assured that no orientation error occurs when it is under the moment of 4 000 Nm. Practice has shown that the approach is effective in solving the orientation error varying.
2013, 42(3): 703-708.
In order to realize the real time evaluation of atmospheric turbulence parameters, a real time measurement platform for adaptive optics (AO) system based on FPGA and DSP, which consisted of a front -end FPGA module and a back -end DSP module, was proposed and built. As the processor of front -end module, a FPGA was used to reconstruct the open -loop Zernike coefficients quickly from closed -loop data with the multi -channel parallel architecture and the pipelining operation. With the characteristic of flexible program, a DSP was used to calculate the back-end complex statistical values for the coherence length r0, the outer scale L0, the wind speed v and the coherence time t0. This proposed platform was applied to the 127 -element AO system for the measurements of atmospheric turbulence parameters based on the observations of stellar stars.
2013, 42(3): 709-715.
Taking pose measurement of non-cooperative space vehicle as research background, a new pose measurement method using multiple cameras with non-overlapping or slightly overlapping views was proposed to solve the problem that monocular vision-based method can not complete the pose estimation in close and ultra-close range, because of the limitation of the imaging space and the field of view, a monocular camera can not observe all the visual features used for pose estimation. Firstly, multiple cameras were configured in non-overlapping form, and the rotations and translations between cameras were calibrated. Then different cameras photographed the different features on the target, the underlying information from different cameras were both redundant and complementary, which provided adequated visual and geometric features for pose measurement. Finally, all the features information from different cameras were fused according to the relationship between cameras to calculate the pose in closed form solution. The experiment results demonstrate its effectiveness and superiority of the method for pose estimation for large target in close and ultra-close range.
2013, 42(3): 716-722.
In order to obtain the figure error of the whole large convex aspherical mirror, a new method for testing large convex asphere by subaperture stitching and interferometry so called SSI was proposed. A perfect sphere mirror was used as the reference surface, the phase distribution of each subaperture could be measured by the digital wavefront interferometer, and the full surface map could be calculated by stitching several subapertures. The basic principle and theory of SSI were studied, the stitching process and prototype for test of large aspheres were devised and developed, and the setup of SSI for measuring of large aspherical surface was designed and manufactured. A convex SiC asphere mirror with the aperture of 260 mm was tested by SSI with 9 subapertures. For the validation, the aspheric mirror was also measured by null compensation, the difference of PV and RMS error was 0.043 and 0.021, respectively ( is 632.8 nm). It provides an another accurate testing method for aspherical surface especially for large convex aspherical mirror.
2013, 42(3): 805-809.
Acousto-optic interaction equations were established separately under two situations of without or with the consideration of ultrasonic attention and the angular distribution of ultrasonic power. The transfer function in spatial-frequency domain between the diffracted light and incident light was derived by employing spatial Fourier transform approach. Numerical simulation was performed. The results indicate that due to ultrasonic attenuation, the peak intensity of diffracted light deviates from the center of the beam and the distribution of diffracted light intensity is not Gaussian type any more, which leads to the pointing deviation of transmitting terminal in inter-satellite optical communications. The study of the dependence of the distribution of diffracted light intensity on ultrasonic power and ultrasonic frequency shows that the peak intensity deviation of the diffracted light can be eliminated when a certain value is chosen for the ultrasonic power. This certain value was defined as the optimal ultrasonic power Popt. The relation between optimal ultrasonic power and ultrasonic frequency was given by applying a polynomial fitting to various Popt in the whole bandwidth of acousto-optic deflector. The pointing deviation due to ultrasonic attenuation can be compensated by adjusting the ultrasonic frequency and ultrasonic power synchronously according to the expression of polynomial fitting.
2013, 42(3): 810-813.
Fiber Bragg grating (FBG) sensor and resistance strain gauge sensor were fixed on the uniform strength beam. Vibration detection characteristics of two kinds of sensors were investigated. The advantage and disadvantage of two kinds of sensors were compared. Vibration was caused by a motor which was fixed at the end of uniform strength beam. The vibration signal in time domain was measured, which was monitored by FBG sensor and resistance strain gauge sensor simultaneously, and the frequency spectrum was analyzed from the vibration curve through FFT. The results show that the vibration graph monitored by FBG sensor is consistent with the vibration graph monitored by resistance strain gauge sensor. But the frequency spectrum monitored by FBG sensor has second harmonic and third harmonic obviously. The frequency spectrum monitored by resistance strain gauge sensor has weak subharmonic. The experiment investigation also indicates that the vibration signal can not be monitored by resistance strain gauge under the electromagnetic interference conditions, but can be monitored by FBG sensor.
2013, 42(3): 814-822.
The detection of infrared small targets under the condition of complex background is one of the most important technologies and the most popular research topics in infrared auto target search and infrared guarding systems. In order to detect the small target efficiently, the local gray mean was proposed to determine the size and location of the infrared small target based on the analysis of the characteristics of the small target and its local background. Firstly, the necessary condition to judge whether a pixel was a small target was given. Secondly, based on the pixels which was the target, the possible sizes of the small target could be figured out. Then, the result was optimized and false alarm was eliminated as far as possible. Finally, according to the result obtained from the first three steps, the ultimated size and location of the infrared small target were given. Matlab simulation results show that, for the complex cloud backgrounds, the detection algorithm based on Top-Hat transform has good detection speed, but when the gray values of false alarm and target are equal, the algorithm could not detect the target efficiently. When choosing suitable parameters, the new algorithm not only can accurately give the location information of the small target, but also has good ability to estimate the small target size. However, the detection speed of the new algorithm remains to be further improved.
2013, 42(3): 823-828.
A biologically-inspired model for the computer vision community was proposed. At first, a set of basis functions that accorded with visual responses to natural stimuli was learned by using eye-fixation patches from an eye-tracking dataset. Then image calculation model was established and features was derived based on the principle of sparse representation: including global continuity, regional color contrast, and local complexity contrast. And then refer to the principle that activity in cells responding to stimuli, a new feature combination theory was proposed to achieve features fusion. Afterwards, some experiments extracting regions of interest from typical scenes prove that this algorithm has superiontity than other algorithms, and the algorithm was applied in virtual and reality interactivity. It can effectively extract effective regions and eliminate virtual scene area.
2013, 42(3): 829-835.
Due to the requirement for prediction of nonlinear target trajectory in image sequences, a sliding window kernel ridge regression(KRR) target trajectory predicting algorithm was proposed. The full KRR which posses the bias item was deduced first, and then the iterative form of sliding window KRR algorithm was also derived in this paper. The algorithm was carried out in a sliding way, and the trajectory information in latest frames was used to predict the position in the next frame, which was achieved by using the KRR. The experimental results demonstrate that the proposed algorithm can predict the nonlinear trajectories accurately, and the prediction error is small. The structure of the proposed algorithm is simple and practicable in engineering application.
2013, 42(3): 836-841.
An improved multi-model image registration method was proposed for visible and infrared image registration, which was based on optimal region mutual information (MI) and edge orientation correlation (OC). Firstly, with proper principle, local regions with rich information were selected by image partition. Then, in order to include spatial information, image edge orientation was introduced to construct an edge orientation map. Finally, by integrating the correlation of edge orientation map and MI of optimal regions with a trade-off weight, a new similarity metric was constructed. Experiment results show that by combining edge orientation correlation, this new metric can effectively improve the accuracy of MI based method, and processing with local optimal regions instead of whole image can improve the efficiency.
2013, 42(3): 595-598.
For applications in coherent optical communications in space and coherent laser detection, the linewidth, noise and tuning characteristics of nonplanar ring lasers were studied systematically in experiment. The output power in single frequency reached 752 mW, with 42% optical-optical efficiency and 54% slope efficiency. The laser linewidth was measured by delayed self -heterodyne interferometry technique. Linewidth decreased with increased pump power. The linewidth was smaller than 1 kHz with output power smaller than 200 mW, and the linewidth was 2.3 kHz at highest output power. Laser intensity noise was mainly attributed to relaxed oscillation. The relative intensity noise (RIN) decreased with increased pump power. The RIN was -93 dB/Hz at 1.78 W pump power. The laser frequency could be tuned by temperature and PZT. Thermal tuning range reached 62 GHz. PZT tuning range was 130 MHz with 100 kHz response bandwidth.
2013, 42(3): 599-604.
The dynamic response of fiber ring resonator has an important effect on the sensing applications. To suppress the dynamic response, the reason of dynamic response was analyzed by the multi -beam interference theory and the critical oscillation conditions of dynamic response were obtained. Furthermore, experiments were designed to analyze the effect of excitation power on the oscillation conditions and the experimental results agreed with the theoretical analysis well. Meanwhile, to avoid of the interference coming from dynamic response, the effect of modulation parameters on the oscillation intensity was made. It provides a reference for the estimation of error in the sensor system.
2013, 42(3): 605-610.
The output voltage of each channel of the four-quadrant tracking system under changing temperature was measured, and a model used to correct the spot center coordinates was established, which was used to compensate the deviation caused by temperature changes. The uncertainty of spot location was reduced via controlling temperature of circuit system operation. According to the photoelectric detection system signal processing way, center coordinate of light beam may be calculated with intensity magnitude of received light pulse of each quadrant. Output characteristics of the four-quadrant tracking system were also tested, the linear operation range of the system was determined which ensured the spot on the best measurement area of the four-quadrant detector. Under circuit system environment temperature controlled, the tracking resolution is 1 m, which is dependent on the step accuracy of stepper motor which is controlled by microcomputer.
2013, 42(3): 611-615.
Acquiring the direction information from the laser threat is one of the most crucial techniques of laser warning. This paper focused on a novel method which based on cylindrical lens and measuring laser incident direction with non-imaging mode to acquire the direction information. The laser warning system was composed of two perpendicular linear array devices, each of which included a cylindrical lens group and a linear IRFPA. The laser incident direction was defined by azimuth and pitch angle which could be calculated by the offset of line spot in the IRFPA. The principle of this method, the structure of laser system, the error analysis were mainly discussed in this paper. And a simulation was made in the end. The simulation result shows that this new kind of laser warning system can achieve pitch angle of 16 is valuable for applying laser warning system on motor vehicles, planes and satellites.
2013, 42(3): 616-620.
The intensity distribution and the divergence of the laser diode (LD) output beam are variable with the different operating current and individual differences. The design of conventional diffractive optical element(DOE) to shape LD beam depends on the intensity distribution of the LD input and output beam, so the tolerance for the input LD beam is very small. A DOE array was put forward to shape the LD beam into three rectangles. It consisted of many DOE units, and each DOE unit could shape the corresponding small segment wavefront into needed output shapes, and all light diffracted by all DOE units was super-positioned on the output plane. Using the above DOE array laser shaped method, three rectangles intensity distribution were realized from Gaussian beam with the diffraction efficiency of 90.5% and the uniformity of 96%. When the half divergence angle of the LD varied from 2to 16in slow and fast axis direction respectively, the diffraction efficiency maintain was approximate 90% and its uniformity was more than 95%. When the defocus of the lens to collimate LD beam varied from -16 m to 16 m,numerical experiments indicate that uniformity and the diffraction efficiency of the shaped beam by the DOE array do not vary. The stability of the LD beam shaping system is improved.
2013, 42(3): 621-625.
Synthetic aperture ladar(SAL) is a kind of high-resolution active imaging ladar, which operates under day and night and long distance conditions. Taking the platform of lunar satellite Chang'e-1 as an example, several problems about SAL were ananlyzed based on lunar surface imaging. Then, using the theory of statistical optics, the statistical characteristics and signal-to-noise ratio of detect signal in photo- limited regime were analyzed. Finally, the related parameters and total number of photons of SAL system was derived based on the lunar satellite platform and it was proved to be feasible in theory.
2013, 42(3): 626-630.
Terahertz time-domain spectroscopy (THz-TDS) technique is a new technology that can be used for non-destructive testing (NDT), research of molecular dynamics, the nature of crystal, structure and conformation of biological molecules etc. In this work, based on THz -TDS technique, antibiotics of four representative penicillin antibiotic drugs (sulbenicillin sultamicillin, mezlocillin, ticarcillin) were investigated. THz spectral features of antibiotics were studied with the method of both experimental measurement and theoretical analysis. This material was identified through testing the absorption and index of refractive. The experimental results show that the absorption spectra of the four antibiotics between 0.40 -1.60 THz are obviously different, which are therefore the fingerprints of them. The research indicates that THz -TDS technique is very suitable for the detection of antibiotics which have slight difference in chemical structure, and the antibiotic medicine can be distinguished clearly by their THz fingerprint spectra.
2013, 42(3): 631-636.
Terahertz fiber is one of the essential components in the terahertz system. In order to realize minimum low loss and dispersion of terahertz transmittion, a novel hollow terahertz fiber was designed and optimizated, which was based on Topas COC. Using the commercial software COMSOL based on the full-vector finite element method, the transmitting characters of this hollow terahertz fiber were calculated and the effects of the structural parameters on transmitting THz wave in the porous fiber core were analyzed. The research shows that adopting designed porous structure can confine the mode energy in porous core, and obtain small mode area, low propagation loss and nearly zero ultra-flattened dispersion. Increasing rate of the hole diameter to the hole spacing, the more mode energy can be confined in the porous fiber core, and the effective mode area and effective mode loss were reduced, but the confine loss and dispersion would be enlarged simultaneously.
2013, 42(3): 637-642.
A simulation test method on electric-optic countermeasure to real laser seekers was proposed to get high reliability of real laser seeker and sample quality of simulation, and the major error factor was found. It was diagrammatic how the process of test worked, and the steps of test were given. According to the characteristic of diffuse reflection target and direct irradiated equipment, the models of laser energy density for diffuse reflection target and direct irradiated equipment at the point of laser seeker were established, and the error distribution principle was analyzed numerically. Besides, it was defined how to get the valid distance with error. The real jamming tests were performed to a real seeker by an electro- optic countermeasure system. The conclusion is that the jamming to laser guided weapon was valid by the electro-optic countermeasure system, and the valid distance also was given. The method was proved to be effective by the tests.
2013, 42(3): 643-647.
Laser warning system is a type of electro-optic countermeasure equipment, which can detect the wavelength and azimuth of the incident laser. Based on the principle of the grating diffraction, DSP signal acquirement and processing system, a laser warning system was designed and realized, which could detect the wavelength and the azimuth of the incident laser, and send out alarms. The design of hardware and software were studied in the paper, the math model of the grating diffraction was built, the math expression of the calculation of the wavelength and azimuth was deduced, then, the laser system experiment was studied. Experimental results showed that it can detect the laser and send alarms immediately, and measure laser wavelength and incident direction, the range of the wavelength and the incident is 500 -1 100 nm and 13respectively, the maximal error of wavelength is 10 nm, and the maximal error of incident direction is 1.
2013, 42(3): 723-726.
In order to increase the flexibility of optical signal demultiplex, a polarization-independent two-port multi-wavelength tunable filter was designed based on the electro-optic effect of birefringent lithium niobate (LiNbO3) crystal. On each arm of an asymmetric interferometer, mode-coupled electrode and phase -shifted electrode periodically alternated cascaded were set to realize mode conversion. Z - transform was utilized in analysis of Jones matrix to get the values of needed driving voltages to select wavelengths simultaneously. Narrow -band multi -wavelength with arbitrary distribution was simulated successfully in free spectrum range (FSR). 100% transmittance was obtained at each wavelength. The number of wavlengths had an influence on sidelobe of each wavelength. And sidelobe of 12 dB could be realized when three wavelengths were selected. Interleaver could also be obtained using this method, which had a flat passband and sidelobe of more than 20 dB.
2013, 42(3): 727-732.
To design new-style effectively optical devices such as filters, amplifiers, attenuators and switches, the transmission characteristics of one-dimension photonic crystal(AB)m(AABAABAABAA)n(BA)m were studied by the transfer matrix method theory. The results show that with the real or complex dielectric constant, (AB)m(AABAABAABAA)n(BA)m will be formed into quantum-well structure photonic crystal which presents an apparent quantized effect. The number and frequency location of the transmission peaks of the thus-formed photonic crystal are closely related to the value of n. When nB is a complex dielectric constant with a negative imaginary part, the transmission peaks in the well present transmission gains and amplification at various levels. The transmission gains even reach as high as 103, and at some transmission peaks, strong stimulated radiation up to 104 orders of magnitude are found. When n3, both the multiple of the transmission gain and the maximum of stimulated radiation decrease with increasing n. And when nB is of a complex dielectric constant, peaks obviously show attenuated in the transmission. These characteristics offer theoretical guidance for preparation photonic crystals.
2013, 42(3): 733-737.
Periodic bottle beam is a beam that has high practical value on scientific research. A novel axicon for generating periodic bottle beam was proposed. It was designed by grinding a conical surface whose dimension and conical angle were smaller than body in the middle of element bottom. The beam transformation property of this element was analyzed with geometrical optics theory, and the conclusion shows that its property is the same as the combination of two normal positive axicon with different conical angle. Besides, the relevant parameters were also calculated with geometrical optics theory. The intensity distribution was simulated by diffraction and interference theory. The results are basically consistent with the geometrical optics. The research shows that when a plane wave illuminates on the novel axicon, periodic bottle beam is formed.
The effect of the arrange of LC molecular on the transmission spectrum in the one-dimensional photonic crystals of a turn of the TiO2 and SiO2 dielectric film was studied, parallel and twist, respectively. It appeared four transparent peaks in photonic band gap when parallel orientation of the nematic LC, the central wavelengths were approximately at 1 840, 1 814, 1 466 and 1 423 nm. Then heating the device, the peak position would blue shift, and the adjacent transparent peak would overlapping. It appeared two independent transmission peaks in photonic band gap, whose position were at 1865, 1489nm, respectively, when twist arrange of the nematic LC. Heating sample, the peak position appeared blue shift. The refractive index anisotropy was more pronounced in the nematic LC layer of the parallel orientation and had two polarization transparent peaks. However, with the twist arrange of the nematic LC, refractive index anisotropy was not obvious, photonic band gap only had one independent transparent peaks. LC molecular orientation could be changed when heating sample, and causing the effective refractive index of the LC layer change, so that to move the position of transparent peaks.
2013, 42(3): 742-746.
Low loss optical coatings mirror is the most critical elements for resonant cavity of ring laser. In this paper, low loss high reflective coatings working at the angle of 45were designed and prepared. In order to improve optical properties of low loss high reflective coatings, high temperature thermal treatment was chosen and the impact of thermal treatment on transmittance, scattering, surface roughness and phase shift of low loss high reflective coatings was researched. The impact of thermal treatment on scattering and surface roughness was very low. With the increase of annealing temperature, the phase shift of low loss high reflective coatings reduced gradually. When the annealing temperature was 550, the optical stability of ring laser output energy was the best. After working for 230 hours, laser output energy dropped to 90.5% of its initial value. The results have shown that optical properties of low loss high reflective coatings and output energy properties of ring laser can be improved by the proper thermal treatment.
2013, 42(3): 747-751.
Aerial remote sensor is very important for obtaining ground information. For high-mach flight condition, the mathematical model of optical window is the foundation for developing research on remote imaging. The shape and refractive index distribution of optical window are affected by high-mach flight condition, so that the image quality of remote sensor would also be affected. It is necessary to establish mathematical model of optical window in order to improve image quality. Firstly, optical window under high-mach flying condition was described and input parameters and boundary conditions of analysis were defined. Secondly, the temperature field model and deformation model of optical window were established. Then, the characteristics of refractive index was presented as a function of temperature. Finally, the mathematical model of optical window under the condition of high-mach flight was derived.
2013, 42(3): 752-757.
The long-circular mirror were optimized with the finite element technology. It could reduce the mass of reflector in space optical remote sensor and minish shape error of the mirror, which was running in the bad environment of the space. Firstly, the reflector was lightweighted and optimized in terms of supports location and structural topology. Secondly, the flexible support was optimized. A new flexible hinge was stated out. The radial deformation was usually not matched between mirror and its backplane because of different coefficients of expansion. The problem was solved with flexible support and the mirror shape accuracy was improved. The maximum value of RMS error, 14.6 nm, was less than the design requirements,/30 (=632.8 nm). The first -order natural frequency is bigger than 100 Hz which shows that the optimization design method is reasonable and feasible.
2013, 42(3): 758-766.
Modeling and analysis of space target's optical scattering characteristics are the premise and foundation of the demonstration, design and performance evaluation of space optical surveillance system. The visible and laser scattering characteristics of space object were emphatically focuced in this paper, and the basic research contents and methods were discussed. The typical BRDF models of satellite's surface materials were introduced firstly, then the advances of foreign and domestic typical researches were introduced from three respects including surface materials' BRDF measurement and modeling, satellite's visible scattering characteristics measurement and calculating, and satellite's LRCS measurement and calculating. At last, the development orientation was put forward, which could provide references for the next research thinking and methods.
2013, 42(3): 767-773.
Drift angle distribution of elliptic solar synchronic orbit was discussed with an image simulating method based on orbit elements and TDICCD imaging mechanism. Image quality was evaluated based on PSF distribution of the simulated final image, and drift angle calculation was carried out. Results show that drift angle of elliptic orbit is linear to half -major -axis and cubic polynomial to orbit eccentricity when argument of perigee is 0. Image quality distribution aimed at KH-12 camera's critical inclination orbit due to angle drifting in case MTF 0.95 was discussed. Results show that smaller drift angle at neighborhood of the perigee of elliptic orbit and higher image quality can be achieved under same integral number.
2013, 42(3): 774-779.
Focusing in optics was extended to spectral dimension in this paper, and the method of spectrally focusing was proposed. The spectrally focusing was implemented by adaptively tuning of a F-P optical cavity tunable filter, which was controlled by the parameters from the regulation and control function driven by the differences between interesting object and its background. An hyperspectral imaging IR system with spectrally focusing was introduced, and the practical scheme of main subsystem was contrived, the mechanism and approach to spectrally focusing were investigated. With spectrally focusing, spectrally adaptive detection can be achieved, the hyperspectral images can be utilized more efficiently, and thereby the ability demand for image processing is reduced. Spectrally focusing conduces to make hyperspectral imaging IR system more rapid and compact, which suits with the utilization in missile or UAV.
2013, 42(3): 780-786.
Temperature, precipitation, solar radiation and soil fertility are important ecological factors for wheat grain protein content (GPC), which are combined with remote sensing data to monitor GPC in this research. Experiments were carried out in suburban areas in Beijing. Multi -temporal HJ1A/B satellite data, meteorological data for the whole growing season from the corresponding meteorological stations, soil nutrient data and GPC obtained at maturity were acquired. Spectral GPC model, ecological factors GPC model and spectral ecological factors GPC model were constructed respectively. The results show that NDVIgreen corresponding to May 11 (around anthesis stage ) has best correlation with GPC in the research area. The correlation coefficient reaches significant level, thus May 11 was the best time for monitoring GPC by remote sensing. NDVIgreen values on May 11 were used for constructing spectral GPC model and spectral ecological factors GPC model. F-test shows that spectral GPC model, ecological factors GPC model, spectral ecological factors GPC model reach extremely significant levels with determination coefficients of 0.782, 0.635, 0.843, and relative error of 0.151, 0.123, 0.049 respectively. The results indicate that accuracy of spectral ecological factors GPC model combined with remote sensing data and ecological factor is higher than GPC model based on only spectral data or only ecological factors. Introduction of ecological factors into spectral protein GPC model helps to improve monitoring accuracy and agricultural mechanism of monitoring models.
2013, 42(3): 787-797.
Research on bidirectional reflectance characteristics of vegetation canopy is an important direction for quantitative remote sensing. The self-developed multi-angle observation system in this paper was used to collect imaging data of soybean in different sowing density from branch period to flowering period. Characteristics of changes in Bidirectional Reflectance (BR) for pure vegetation and mixed canopy, including vegetation and soil, were analyzed by hyperspectral images from segmenting vegetation, background soil, and shadow leaves. Studies have shown that observation position is the principal plane; canopy reflectance of pure vegetation after soil spectra is removed, gradually increased along with the decrease of zenith angle. When forward observation was conducted in principal plane, it differed from the canopy composed of vegetation and soil. When observation direction changed from backward to forward in the principal plane, canopy reflectance of pure vegetation in visible and near-infrared region showed a growing tendency gradually and the soil spectra was removed, this was different from before. In addition, when the observation position was in a perpendicular plane, there was a similar change for reflectance of soybean canopy before and after soil spectra was removed; but the symmetry of canopy reflectance of the former was better than the latter. The results had similar trends with BR change of soybean canopy in different sowing density. The paper provides a basis for the development of multi-angle remote sensing.
2013, 42(3): 798-804.
Red edge parameters are widely used to inv ersely deduce crop parameters in quantitative remote sensing studies. Among them, the red edge position, as a very sensitive indicator for monitoring crop stress, is strongly correlated with crop biochemical components. Accurate estimation of the chlorophyll content of vegetation is of importance for studies on forest health, stress, and productivity estimation, as well as carbon cycle. In this article, several algorithms of red edge position were introduced firstly, their applications were compared, and the leaf chlorophyll content of vegetation was estimated through selecting its different sensitive bands. Then leaf spectral data from indoor spectra were extracted, four algorithms were used (first -order derivative spectrometry, first -order derivative spectrometry after smoothing, four point interpolation, and quintic polynomial fitting) to process spectral data and obtain red edge position variables. Finally the obtained variables were used to fit the chlorophyll content, and various regression models of these algorithms for estimating leaf chlorophyll content were established. The results show that all these established models are feasible to estimate chlorophyll content. Among them, the quintic polynomial fitting method is most accurate, but highly complex in obtaining the red edge position while the four point linear interpolation is next to it in accuracy, but simpler.
