2020 Vol. 49, No. 4
2020, 49(4): 0403001.
doi: 10.3788.IRLA202049.0403001
Panoramic laser fuze usually calculates the optimal initiation time and initiation azimuth only based on single measured target direction and distance, the calculation accuracy is low. On the other hand, fuze can not distinguish the authenticity of targets, it is easy to cause "false alarm" or accidental bombing. Based on the working principle of the synchronous scanning panoramic pulse laser fuze, the direction, distances and position coordinates of multiple detection points were analyzed. The target velocity model based on multiple detection points were established, which can calculate the target speed and judge whether the target was true. The geometric center position of the target feature was solved, and the optimal initiation time and azimuth calculation model were established to obtain the maximum damage effectiveness of the warhead. The influence factors of the optimal initiation time and azimuth were analyzed. The research can provide a reference for the target identification and directional initiation of the panoramic laser fuze.
2020, 49(4): 0403002.
doi: 10.3788/IRLA202049.0403002
The laser fuze can realize omnidirectional detection of missile targets through the circumferential multi-channel layout, its active-rotational-narrow pulse detection method can obtain the information about missile-target distance, miss azimuth angle and target type. At the same time, due to the characteristics of narrow beam and no side lobes, the fuze initiation zone has a small distribution area. All of these factors provide an important technical approach for efficient fuze-warhead coordination. Based on the analysis of the influence factors of air-defense missile fuze-warhead coordination, a fuze-warhead system scheme with eight-channel circumferential laser fuze was designed, combined with missile-target distance, miss azimuth, and target type. The fuze-warhead coordination simulation results in conditions of typical encounter parameters indicate that, the kill probability of single missile could be obtained to a maximum of 10% with the laser fuze information. It is useful for optimal design.
2020, 49(4): 0403003.
doi: 10.3788/IRLA202049.0403003
Aiming at optimal detonation controlling of directional warhead fuze, detonation control simulation for dodecagon-detection laser fuze was presented. Based on dodecagon-detection model, the detonation orientation was controlled by discriminating target orientation. Combining with target vulnerability model, effect of delay time on damage was simulated and analyzed on different trajectories. The simulation results show that it is very important to match the parameters such as fuze delay time, miss distance and fragment fly scattering angle for high-speed small targets in air. When delay time is no more than 2 ms, the average damage probability, if miss distance is within 8 m, is more than 0.6, and is less than 0.5 if miss distance is over 10 m. The model can comprehensively analyze the damage effects with different delay time and miss distances.
2020, 49(4): 0403004.
doi: 10.3788/IRLA202049.0403004
Aerosol-interference is a serious interference source for active optical target-detection device (AOTD) when it is used in lower sky or super low sky. When AOTD in a vehicle passes through aerosol, it may be wrong armed, even give out execution signal before right time. In order to increase the ability in aerosol environment, how the AOTD worked and how the aerosol interfered the AOTD were analyzed. It also showed out the techniques of anti-aerosol-interference used in engineering. The general techniques for anti-aerosol-interference were settings of cut-off distance method, weaken methods by optical parts, optical field restraining method, cancellation by symmetric views, setting reference view field, body recognition method, composite with Ka detectors, decreasing the width of transmitted pulse, image recognition method et al. Among these methods, the multimode detection method was a valuable way. Effects of different anti-interference methods were listed, the results shows integrated application of all the methods can increase the ability of AOTD.
2020, 49(4): 0403005.
doi: 10.3788/IRLA202049.0403005
The detection ability of laser fuze is easily disturbed by smoke, which causes false alarm. In order to study on the backscattering characteristics of pulsed laser fuze in smoke, the relevant model based on Mie scattering theory and Monte Carlo method was established, and the backscattering signal in smoke was simulated using 905 nm pulsed laser. To verify the accuracy of the model, the actual peak voltage was compared with the simulated normalized intensity and correlation analysis was conducted. Then, the backscattering characteristics of the pulsed laser fuze under different smoke concentrations, length of pipes and distances were analyzed. Finally, the influence of different smoke environment was obtained. The results can provide support for the anti-smoke interference of the pulsed laser fuze.
2020, 49(4): 0403006.
doi: 10.3788/IRLA202049.0403006
In order to analyze the performance of coherent laser fuze under cloud and fog interference, the detection model of coherent laser fuze in cloud and fog was created based on Mie scattering theory and Monte Carlo method. Through simulation, the echoes of coherent laser fuze were obtained in various scenes. The time-domain and frequency-domain characteristics of echoes were analyzed, as well as the influence of cloud and fog visibility, detection position, and detection angle on echoes. The results show that the coherent laser fuze can accurately identify the target by using the frequency-domain characteristics, and is not easily affected by factors such as cloud and fog visibility, detection position, and detection angle. The results demonstrate the excellent detection performance of coherent laser fuze in cloud and fog.
2020, 49(4): 0403007.
doi: 10.3788/IRLA202049.0403007
In view of the problem that laser fuze is easily interfered by fog and smoke, a new laser fuze anti-interference method based on pulsed width modulation technique was proposed. The fog echo signal power of different pulse width was computed, and the variation of echo signal power under the influence of transmitted pulse duration was given. The echo signal power ratio in different fog and aerosols environment was analyzed by using different pulse width to detect. The experiment results show that by using different pulse width to detect, the ratio of backscattering power is usually more than 3. Therefore, this method can be used to improve anti-interference ability of laser fuze.
2020, 49(4): 0403008.
doi: 10.3788/IRLA202049.0413008
In the ultra-low altitude detection mode of circumferential laser fuze, range gate compression was used to achieve the ability of anti ground clutter. In order to meet the requirement of accurate and stable height measurement based on ground echo, the characteristics of ultra low altitude ground echo of circumferential laser fuze were studied. The ultra-low altitude ground detection model of circumferential laser fuze was established. Based on the bidirectional reflection distribution function, the power equation in time domain of the ground echo received by the circumferential laser fuze was derived. The laser echo characteristics of the ground were calculated and analyzed under different conditions of missile flight altitude, pitch attitude and ground reflection properties. The results show that the inherent absolute error of height detection by circumferential laser fuze increases with the increase of detection distance, while the inherent relative error decreases. With the increase of pitch angle, the pulse width broadening rate of laser echo pulse increases. The larger the specular reflection component of the bidirectional reflection distribution function of ground, the more sensitive the ground echo power varies with the missile pitch angle. Theoretical support was provided for the anti ground clutter research of circumferential laser fuze under the condition of ultra-low altitude.
2020, 49(4): 0403009.
doi: 10.3788/IRLA202049.0403009
Laser near field detection plays a crucial role in the laser measurement products series and has been successfully and widely applied in lots of field. Traditional laser near field detection system transmits the triggering signal according to the distance information, without being able to judge whether the distance signal is obtained from the target or not. As a result, a false positive could happen and the performance of the system would be weakened. However, recognition based spectral information can improve accuracy. In this paper, a target recognition system, which was compatible for the classical laser fuse scheme, based on spectrum analysis was proposed to increase the detection accuracy of the laser fuse system. Some suggestions about the general design of the improved laser fuse system with spectrum analysis sensor were also offered including active and passive detection with imaging function as an option. Moreover, based on the CMOS technology, a monolithic spectrum analysis sensor was designed and fabricated, which integrated the spectral element on top of the opto-electronical sensor in one chip. Thanks to the greatly reduced size and the weight, this spectrum analysis sensor had potential application in practice. The experiment results show that the capability of such system on chip (SOC) sensor in distinguishing the target from the camouflage.
2020, 49(4): 0403010.
doi: 10.3788/IRLA202049.0403010
In order to meet the multi position initiation requirements of multi-mode warhead, the laser fuze needs to simultaneously achieve multi-ranging distances from 1 m to 25 m. For the noncoaxial laser fuze, the range of the detection distance is closely related to the system parameters. Based on system detection distance requirements, the working distance calculation model of the noncoaxial system was established, the influence of the system parameter changes of the laser fuze on the nearest working point and the furthest working point was analyzed. The receiving deflection angle and the center distance between the transmitting and receiving system were variables. In the case of satisfying the constraints, the multi-island genetic algorithm was used to optimize the variables. The optimization result shows that, under the condition of satisfying the constraints, the minimum receiving deflection angle is 90.97°, and the center distance is 0.03 m. The experimental result shows that the designed system parameters can completely meet the requirements of multi-ranging distance. The research can provide reference for the parameter design of laser fuze system with multi-ranging.
2020, 49(4): 0403011.
doi: 10.3788/IRLA202049.0403011
In view of the existing BRDF tests are for planar targets, not for stereo targets, equivalent test method was proposed for stereo targets BRDF. By combining different reflectivity coating child-blocks into corresponding parent-block, stereo target spatial distribution of light scattering was equivalent. BRDF of axisymmetric cylinder target and its equivalent parent-block were tested by using the BRDF measuring system, and the curve correlation analysis was completed. The test results show that the BRDF equivalent method can measure the axisymmetric stereo targets and equivalent BRDF of stereo targets, when incident angle is small, or less than 30°. BRDF equivalent test method of axisymmetric stereo targets can be realized by founding planar ones.
2020, 49(4): 0404001.
doi: 10.3788/IRLA202049.0404001
In the technology of wavefront coding, a special phase mask is put at the position of optical system stop. Then the goal signal wavefront will be coded. At the image processing part, the coded signal will be decoded to the original image. Because the insensitivity of the coded wavefront to the defocus and other aberrations is ten times more, the focus depth will be extended ten times more. So the wavefront coding can solve the defocus and alignment error caused by terrible mechanics and heat environment using coding and decoding. Based on the extended focus depth principle of wavefront coding, an aberration inactivation long/long double bands infrared optical system was designed. The focus depth was extended to be 10 times more. Imaging test was carried out with the wavefront coding prototype. The coding image of the spot-bar was used as the PSF to decode the image at the 10 times defocus position of cross-bar and four-bar. After decoding, the image of cross-bar and four-bar was with high resolution. At the last, the imaging results of wavefront coding were analyzed. The ripple of decoding picture was caused by not enough spatial sampling. After sampling PSF of different field, the ripple could be eliminated by using decoding algorithm of spatial transformation. The signal and noise would be extended at same time while the image was decoding. So the noise suppression algorithm used in decoding should be further researched to satisfy the missile-borne demand of more energy and higher signal to noise ratio.
2020, 49(4): 0404002.
doi: 10.3788/IRLA202049.0404002
The hypersonic vehicle is subjected to intense aerodynamic heating during flight. The temperature of the sapphire infrared radiation (IR) window located in the head rises significantly, and the transmittance decreases while the self-radiation is greatly enhanced, resulting in a decrease in the internal infrared detection gas signal-to-noise ratio. The aero-heating with unsteady temperature rise process of the sapphire IR window and the infrared radiation transmission characteristics of the 3.7-4.8 μm band were numerically simulated. The results show that the average temperature can't accurately reflect the infrared transmission characteristics of the sapphire IR window and its impact on the sensitivity of the infrared detector. There is an optimal infrared detection window thickness in which the sensitivity of the infrared detector reaches best.
2020, 49(4): 0404003.
doi: 10.3788/IRLA202049.0404003
A GPU parallel computing method for infrared target imaging was established, in which skin and plume was included. The SLG model was used to calculate the infrared characteristics of the radiation gases, and the LOS method was used to solve the infrared radiation transmission equation of the plume. According to the imaging geometry relationship between the surface and the three-dimensional plume, a target projection algorithm was established, in the method the forward ray tracing method was used to calculate the surface radiation imaging, and the reverse ray tracing method was used to calculate the plume radiation imaging. The CUDA parallel method was used to increase the calculation speed in the skin projection calculation module and the plume radiation calculation module, and the fast calculation of the target infrared spectrum image at the entrance of the detector was realized. The results show that the projection imaging algorithm can accurately generate the target image under the set conditions. The radiation distribution of the target infrared image is consistent with the temperature distribution. The calculation result of the tail flame radiation intensity is in good agreement with the experimental results. The CUDA parallel algorithm can effectively improve the computational efficiency of the program, the calculation speed of the skin projection module can be more than hundred times when the amount of calculation is large.
2020, 49(4): 0404004.
doi: 10.3788/IRLA202049.0404004
The digitalization of infrared focal plane arrays (IRFPA) is an important direction for the development of IRFPA, the core of which is the integration of high-performance analog-to-digital converter (ADC) in the readout circuits. In this paper, the digital outputs of readout circuits were discussed to evaluate the performances of IRFPA. Otherwise, the static and dynamic testing methods of column-level ADC in IRFPA were elaborated. Among them, the static performances of ADC were tested based on oversampling principle which improved the testing correctness of the no-missing code resolution. For the ADC static and dynamic testing requirements, combined with Labview software and digital signal acquisition equipments, a testing platform of high-performance ADC was built. Through testing a digital IRFPA, it is verified that the testing method and platform can be used for testing evaluation of column-level ADC in digital readout circuits.
2020, 49(4): 0404005.
doi: 10.3788/IRLA202049.0404005
Terahertz passive imaging technology has many unique advantages and has become an important research direction in the field of security inspection. In order to further improve the imaging performance and practicability of the terahertz passive imaging system, the performance of a terahertz passive imaging system based on opto-mechanical scanning developed by our laboratory was studied. By exploring the influence of different system parameters and experimental conditions including its imaging speed, distance and the status of detector on the performance of imaging system such as the image resolution and background noise, the optimized system parameters were obtained. At the same time, the performance of imaging system to detect the human body hiding the metal objects was explored. It was shown that the system was suitable for the security inspection of human body. The experimental results show that the imaging distance of the terahertz passive imaging system is within the range of 1.5–2.5 m in front of imager, that is, its depth of field is about 1 m. The imaging speed of system is 2–4 seconds per frame. Moreover, the operating level and gain of detector have a great impact on image sharpness and system noise. There exists an optimized operating state of detector. Under the optimized condition, the clear terahertz images can be achieved and the resolution of target was 1.5–2 cm. Our imaging system can clearly detect metal objects hidden under human body’s clothes and substances with strong absorption on terahertz waves.
2020, 49(4): 0405001.
doi: 10.3788/IRLA202049.0405001
Mode is the fundamental concept in fiber optics, which is one of the most concerned issues in the fiber laser research. However, the mode degeneracy issue has not been clarified in common literature. By the classical electromagnetic theory, the degeneracy of vector mode and linearly polarized modes was analyzed and the relation between vector mode and linearly polarized mode were discussed in this paper. In the weakly guiding step index fiber, the vector mode and the linearly polarized mode were both the orthogonal complete basis for describing the optical field. The optical field described by vector mode [HE1n(o)、HE1n(e)] and linearly polarized mode [LP0n(ye)、LP0n(xe)] were 2 dimensional; the optical field described by vector mode [TE0n、HE2n(o)、HE2n(e)、TM0n]] and linearly polarized mode [LP1n(yo)、LP1n(ye)、LP1n(xo)、LP1n(xe)] were 4 dimensional; the optical field described by vector mode [EHm-1n(o), EHm-1n(e), HEm+1n(o), HEm+1n(e)] and linearly polarized mode [LPmn(yo), LPmn(ye), LPmn(xo), LPmn(xe)] were 4 dimensional.
2020, 49(4): 0405002.
doi: 10.3788/IRLA202049.0405002
Compared with the DFB laser, the TDLAS laser gas detecting system using the VCSEL laser as the detecting light source has the advantage of low power consumption. According to the characteristic of the low power TDLAS gas detection signal, combined with the characteristics of modulation VCSEL laser source, a laser driver, signal acquisition and processing were designed, and a low-power TDLAS methane (CH4) gas detector based on WMS was designed. The absorption peak of CH4 molecule near 1653.7 nm was selected as the absorption line, and the second harmonic (2f) signal was extracted by a lock-in amplifier. The response of different concentrations of CH4 detection was studied experimentally, and the 2f signal's amplitude was recorded and linearly fitted. The results show that the CH4 concentration has a good linear relationship with its 2f signal's amplitude, and the linearity is 0.9998. Accuracy of the detection system is better than 10% in the range of 50 - 500 ppmv, and the detection limit is 10 ppmv. With the long-term detection of 250 ppmv of CH4 for 10 h, the fluctuations are less than ± 2.4%. Allan deviation analysis was introduced. When the initial integration time was 1 s, the Allan deviation was 9.9 ppmv. When the integration time reached 359 s, the Allan deviation was 0.06 ppmv, which indicated the good stability of the system.
2020, 49(4): 0405003.
doi: 10.3788/IRLA202049.0405003
An all fiber linearly polarized narrow-linewidth nanosecond pulsed fiber laser based on master oscillator power amplifier (MOPA) structure was reported. The pulsed seed was generated by modulating a single-frequency distributed feedback (DFB) fiber laser using an electro-optic intensity modulator. In order to suppress stimulated Brillouin scattering (SBS), the pulse width was set to be 3 ns and the linewidth of seed was broadened to be 2.9 GHz by a phase modulator. After amplifying by two stages polarization maintaining Yb3+ doped fiber amplifier chain, the output pulse laser was obtained with an average power of 142 W, a repetition rate of 1 MHz, a pulse duration of 2.88 ns, corresponding to peak power of 49.3 kW. At maximum output power, the laser beam quality M2 was ～ 1.15 and the polarization extinction ratio(PER) was >15.4 dB.
2020, 49(4): 0413001.
doi: 10.3788/IRLA202049.0413001
Structured light-assisted stereo vision technology can solve the problem of the measured object with sparse characteristics, so as to realize the high precision measurement of the geometric dimension of the object.The method of using the polar line and the fringe order double constraint was proposed, which was based on the principle of polar constraint in binocular camera and fringe order in multi-frequency heterodyne. Using this method, the stereo matching area was reduced. And during the stereo matching process, a weighted image template was used, the initial matching point was determined by using the phase information and the similarity template matching method, and the sub-pixel matching was realized by the two-dimensional curve fitting method according to the spatial distance and the phase difference of the initial matching point and the polar line. Experiments show that the method is applied well in small field of view measurement, and can achieve fast and accurate measurement for spheres with a diameter of 10 mm.
2020, 49(4): 0413002.
doi: 10.3788/IRLA202049.0413002
The fusion of laser range finder (LRF) and visual image has received more and more attention in recent applications such as industrial robots. The calibration of the poses of these two instruments was conducive to the effective fusion of the two information. The single-point laser range finder and the camera's pose fusion were the main research contents. Two calibration methods for determining the relative position and direction of the two were proposed. Based on the coordinates of the spot camera, the spot was visible and the spot was invisible as the research content. The research content establishes the calibration equations for the two cases by the coordinates of the spot and the plane constraint respectively, and the validity and reliability of the two calibration methods were verified by experiments. The experimental results show that the calibration results can be made in the case of a limited number of measurements. The re-projection error is within 3 pixels, and the computation time is greatly reduced.
2020, 49(4): 0413003.
doi: 10.3788/IRLA202049.0413003
In the ground test of multi-vehicle, the global motion estimation method based on graph optimization model was proposed in order to reduce the cumulative error of posture estimation due to the discontinuity of tracking trajectory caused by tracking algorithm. Firstly, a ground test vision motion estimation system for vehicle was established. Then, according to the number of feature points on the vehicle, a vector crossover method was proposed to solve the position of vehicle posture, and the estimation value of vehicle posture with good data correlation was obtained. The intermediate coordinate system method was used to solve the value of the initial position node of the track segment under the measuring coordinate system, and finally, under the framework of graph optimization theory, the nonlinear global optimization of the motion estimation results of the vehicle during the whole measurement process was carried out to reduce the cumulative error of the linear algorithm, and the feasibility and precision of the vehicle motion estimation algorithm were verified by simulation and practical experiments. The experimental results show that the accuracy of the proposed vehicle attitude estimation algorithm can reach 0.5° (3σ) and 3 mm (3σ) respectively, and the actual absolute measurement accuracy can reach 1.3° (3σ) and 4 mm (3σ) respectively, the size of the vehicle is 400 mm in the range of the measuring range of 6 000 mm×6 000 mm×3 000 mm and the three-dimensional positioning accuracy of the feature points is 2.9 mm. It basically meets the requirements of ground test for the development of multi-vehicle formation algorithm and the performance evaluation of guidance control system, stable and reliable, high precision and strong anti-jamming ability.
2020, 49(4): 0413004.
doi: 10.3788/IRLA202049.0413004
For the purpose of inspecting the film cooling holes on high-pressure turbine blade in a rapid and accurate manner, a non-contact four-axis vision coordinate measuring system was designed and established in the paper. With regard to the determination difficulty of the spatial location of the rotary axis, a calibration method based on vision measurement was proposed in the paper, which fully considered the imaging characteristics of industrial CCD used in the system. In the calibrating procedure, a specially designed cuboid mental block was applied as the target. Through the coordination between the turntable and the coordinate measuring machine, the industrial CCD focused on the block surface and then captured the sharp edges of the block. And then, the spatial orientation of the rotary axis in the machine coordinate system could be determined by edge extraction, pixel distance calculation, physical distance conversion and algebraic operation etc. Finally, a gauge block was selected to be inspected by the measuring system to verify the calibration method and results, whose nominal size was 80 mm. As the experimental results showed, the measuring errors were all smaller than ±0.01 mm. Therefore, the calibration method of rotary axis proposed in the paper showed higher calibration precision and repeatability, which could meet the inspecting requirements of the shape and position parameters of film cooling holes.
2020, 49(4): 0413005.
doi: 10.3788/IRLA202049.0413005
Based on the theory of vortex beams and spherical wave interference, an optical measurement method for object micro-displacement was proposed. After improving the Mach-Zehnder interference optical path, a vortex beam was generated as a reference beam, using the spatial light modulator illuminated by a beam of light, and another beam was transformed into a spherical wave through the lens and illuminated to the object. The interference fringes were distributed in a spiral shape as the two beams interfered. When the object has a micro-displacement, the optical path difference of the two beams changes, and the spiral interference fringe rotates. Noticing this phenomenon, the micro-displacement of the object can be determined by the rotation angle of the spiral interference which vortex beams interference with spherical wave. Through theoretical analysis, simulation and experiments have proved that the micro-displacement of the object can be monitored in real time, and effectively calculated by the rotation angle change of spiral fringe based on interference of vortex beams and spherical wave. In the experiment, the displacement of the measured object is 27 nm, the actual measured displacement of the object is 25.75 nm, and the error is 1.25 nm compared with the theoretical value.
2020, 49(4): 0413006.
doi: 10.3788/IRLA202049.0413006
A system of Swept-Source Optical Coherence Tomography for synchronous measurement of the eye axis with large imaging depth range and anterior segments was proposed to solve the problem that traditional ophthalmic axis measuring instruments can not achieve the functions of large imaging depth in axial measurement and imaging on anterior simultaneously. The proposed system increased the imaging depth by designing a infrared swept source with wide range. Then a calibrated optical path was built for k-domain resampling to improve the imaging quality in large range interference. Thus the high precision axial information and the anterior segment image could be obtained simultaneously. To solve the problem of low SNR of OCT images in this system, an edge-preserving denoising algorithm based on anisotropy filtering was proposed to suppress the speckle noise, which effectively improved the image contrast. Using the equal-proportion human eye model and vitro fish eye imaging respectively, the experimental result shows that the imaging depth of the system can reach 69 mm. The 12 mm anterior segment can be completely scanned in transverse direction, while the axial five-layer structure is accurately measured. The average measurement error of axial length is 0.04 mm, and the imaging time is about 0.45 s, which fulfil the real-time requirements of clinical medical application.
2020, 49(4): 0413007.
doi: 10.3788/IRLA202049.0413007
The structure layout of one space gas monitoring sensor is very compact. There are eight optical lens, eleven electronic devices and two motors staggered in the small-scale space. There were so many calorific equipments with long working hours and large power consumption, and their temperature control requirements were not consistent with the optical lens, the number of which was also large. Furthermore, one of the two motors was a two DOF turn motor during operating. These above characteristics make thermal design of the gas monitoring sensor a great challenge. To effectively solve the difficult problems of the gas monitoring sensor thermal design, combination of multy design methods were adopted. The thermal behavior of the gas monitoring sensor components were systematically managed based on the idea of thermal management to save thermal control resources. Indirect thermal control technology was used on the optical lens temperature control to guarantee meeting the high precision and stability requirement. Heat dissipation of the two DOF turn motor was achieved by radiation cooling, by which flexible rotating table could be avoided in the cooling path, so that thermal control system reliability could be improved. Finally, structural and thermal integrated design was applied to make sure the requirements of those above thermal design fully guaranteed in structure. The results of thermal balance test show that all components temperature meet the requirements no matter under cold case condition or hot case condition, and optical lens have high temperature stability throughout the life cycle. The maximum temperature fluctuation of all optical lens is less than 1 ℃ under the same case condition. High precision thermal control of optical lens are obtained under the condition of multiple heat source and complex working mechanism.
2020, 49(4): 0414001.
doi: 10.3788/IRLA202049.0414001
The mask spectrometer uses the beam splitter to separate the incident scene into two dimensions: spatial dimension and spectral dimension, then information fusion is used to achieve high spectral resolution of dynamic video signal acquisition. It has wide application value in the field of dynamic hyperspectral imaging. In order to solve the problem of miniaturization of mask spectrometer, for the part of the spectral optical system simplified design of the number of lenses, and the conventional prism was replaced by the grating, the linear dispersion was realized while the structure was further compacted. The problem of stray light generated by the unwanted stages of the grating was analyzed, and the feasibility of the system design was demonstrated. Finally, in the range of 400-1 000 nm, the spectral resolution was less than 4 nm, the average modulation transfer function (MTF) at the full field of view Nyquist frequency was greater than 0.4, and the image illumination uniformity was higher than 0.9, achieved good image quality. Meanwhile, the SNR generated by stray light was 0.06, which did not affect the collection of spectral information.
2020, 49(4): 0414002.
doi: 10.3788/IRLA202049.0414002
Telecentric and cryogenic optical system is a good solution to space-based IR sensor with wide field, sensitivity and determination of accurate orientation. A refractive telecentric optical system was designed with squared field of view in 8 degrees, entrance pupil of 265 millimeters and operating at 200 K. The aperture of the lens was 280 millimeters. By multilevel spring holders,the opto-mechanism got a available tradeoff between enough stiffness at room temperature and stress-free at 200 K, accordingly prevents thermal stress on lens and heat leakage from room temperature supports to cryogenic lens. After lenses alignment, vibration test and image test at operating temperature were performed. The ensquared energy reached 75% on axis and 72% off-axis respectively.
2020, 49(4): 0414003.
doi: 10.3788/IRLA202049.0414003
In order to ensure the surface accuracy of the Pointing, Acquisition and Tracking (PAT) mirror in the harsh space environment, a flexible support structure with grooves on the bottom was designed. Due to the large number of parameters of flexible support structure, in order to avoid serious coupling between parameters, the orthogonal optimization method was used to optimize the parameters of flexible support structure, and then the finite element method was used to analyze the mechanical and thermal characteristics of mirror components. The simulation results show that the first-order frequency of the mirror module is 352.61 Hz, and the maximum surface error RMS under the combined action of 1 g gravity and 10 ℃ temperature rise (temperature drop) is λ/54.79(λ=632.8 nm), which can satisfy the dynamic and static stiffness and thermal dimensional stability. The ZYGO interferometer is used to detect the mirror surface shape in the temperature range of (20±10) ℃. The results show that the PV value of the mirror surface is better than λ/6, and the RMS is better than λ/43, which meets the requirement of RMS≤λ/40. The experimental results show that the design of flexible support parameters is reliable and meets the application requirements.
2020, 49(4): 0414004.
doi: 10.3788/IRLA202049.0414004
Aiming at the particle contamination on the surface of optical components in practical work, based on Mie theory, the absorption of incident laser energy by polluted particles (mainly SiO2) in the air in sandy areas was discussed. In addition, the effects of air cleanliness, orientation of working face and placement time on the surface absorption characteristics of optical components were further analyzed. The results show that the higher the air cleanliness level is, the optical component face up and the longer exposure time are, would make the surface absorption of the optical component stronger. The research results can provide guidance for pollution control of optical system in practical applications.
2020, 49(4): 0418001.
doi: 10.3788/IRLA202049.0418001
The new far-IR nonlinear crystal material PbIn6Te10 has great application potential among 14-25 μm even more than 25 μm because of its special optical properties, including clear transparency(1.3-31 μm), large nonlinear coefficient(d11=51 pm/V) and suitable birefringence(~0.05). The phase diagram analysis combined with the experiment was used to select the appropriate group distribution ratio, the PbIn6Te10 polycrystal was synthesized by high temperature single-temperature zone method(STZM), and single crystal with size of
2020, 49(4): 0418002.
doi: 10.3788/IRLA202049.0418002
Based on the principle of silicon surface film passivation, the effect of different thickness surface passivation film on the electronic sensitivity of back-thinned CMOS (BCMOS) sensor was studied. Firstly, the electron bombardment test was carried out after the back thinning processing on CMOS sensor. The electron bombardment test shows that the gray value of the electronic image presents a linear relationship with the change of bombarding electron energy. Then, the aluminum oxide films with different thickness were deposited on the surface of back-thinned CMOS, and the electron bombardment test was carried out. It was found that the collection efficiency of secondary electron was increased by 14.9% when the thickness of aluminum oxide film was 20 nm, meaning that the electron sensitivity could be improved by surface film passivation. Furthermore, the dark current of the back-thinned CMOS sensor reduced from 1510 e-/s·pix−1 to 678 e-/s·pix−1 with the increase of film thickness. The above results show that aluminum oxide film has a good passivation effect on back-thinned CMOS sensor, which could improve the secondary electron collection efficiency and reduce the dark current of the back-thinned CMOS sensor, and provide a technical support for the development of high sensitivity EBCMOS devices in the future.
2020, 49(4): 0426001.
doi: 10.3788/IRLA202049.0426001
A new asymmetric optical image encryption algorithm was proposed, which combined vector decomposition and phase-truncated. The plaintext was encrypted by four keys to obtain uniformly distributed ciphertext and three decryption keys. The decryption key was generated in the encryption process, which was different from the encryption key. It realized asymmetric encryption and increased the security of the system. The decryption key generated in the process of vector decomposition was strongly related to plaintext. Compared with the existing optical asymmetric encryption algorithms, plaintext was more sensitive to ciphertext and decryption keys. The system was more resistant to selective plaintext attack. At the same time, it also improved the sensitivity of decryption keys. The introduction of phase-truncated enlarged the key space and enhanced the security of the algorithm. Moreover real number ciphertext was produced for easier transmission. The experimental results show that the algorithm has uniform ciphertext distribution and low correlation between adjacent pixels. The decrypted keys and the plaintext to decrypted keys and ciphertext are highly sensitive. This algorithm has strong ability to resist various attack and better optical image encryption effect.
2020, 49(4): 0426002.
doi: 10.3788/IRLA202049.0426002
To provide a theoretical basis for identification and detection of oil spill pollution on the sea surface, based on the polarization reflection coefficient of Fresnel reflection formula and combined with polarization bidirectional reflectivity factor and probability density distribution function of rough sea surface, a perfect pBRDF model was established. Then the polarization reflection distribution function of sea water and oil film was simulated under different solar incident angles, different detector observation angles and different sea surface wind speed and wind directions. The results show that, firstly, P-polarization reflectance reaches 1.0×10−5 and 2.5×10−5 respectively when the solar zenith angle of seawater and oil film is 53° and 56°. S-polarized reflectance increases with the increase of the solar zenith angle. Moreover, the higher sea surface wind speed is, the smaller peak value of polarization reflectance is. Additionally, wind direction only changes spatial position of pBRDF. Finally, the spatial distribution of linear polarization degree between seawater and oil film is obviously different. Experiment platform was set up with the camera working at 40°. The conclusion is obtained that the linear polarization of seawater and oil film is between 0.2−0.4 and 0.5−0.7, respectively. It also shows that using polarization detection to obtain the polarization degree and polarization angle of the target scene can improve the image quality.
2020, 49(4): 0426003.
doi: 10.3788/IRLA202049.0426003
In infrared images, when the traditional histogram equalizes the image, the detail pixels are easily immerged by the background pixels, resulting in the image being too bright and too dark. Based on this situation, an adaptive inverse histogram equalization algorithm was proposed in this paper. The algorithm enhanced image details by inverse statistics, adaptive selection threshold and segmentation mapping. Compared with the traditional histogram equalization algorithm, the inverse histogram equalization algorithm significantly improve the image visual effect in different gray level distributions and enhance the details of different areas of the image to different degrees. Moreover, under the premise of achieving better image processing effects, this algorithm can still guarantee real-time performance and high efficiency by optimizing calculation methods, and is suitable for FPGA hardware transplantation.
