2020 Vol. 49, No. 1
2020, 49(1): 0103001.
doi: 10.3788/IRLA202049.0103001
Due to myriad applications, infrared and terahertz are playing an important role in the fields of spectroscopy, imaging, wireless communication and remote sensing. However, be limited by the low photon energy in the infrared terahertz band, the detection encounters great difficulties, so it is a anenormous challenge to realize infrared and terahertz detection with high sensitivity, high speed and high stability. Two-dimensional materials offer new opportunities for infrared and terahertz detection due to their high mobility, adjustable band gap, and few surface dangling bonds. The development of two-dimensional material infrared and terahertz detectors regulated by photo-hot carrier is in the ascendant. This paper mainly introduced the latest research progress of infrared and terahertz detectors based on photo-hot carrier regulation. This article will expand on materials, device structures, response bands, and response mechanisms.
2020, 49(1): 0103002.
doi: 10.3788/IRLA202049.0103002
Antimony telluride (Sb2Te3) is a new type of two-dimensional layered material, in this paper, the "top-down" ultrasonic exfoliation method was used to prepare antimony telluride quantum dots (Sb2Te3 QDs) for the first time, with antimony telluride powder as raw material, and N-methyl pyrrolidone (NMP) as the dispersant. A variety of characterizations(SEM, TEM, AFM, XPS, XRD, etc.) for the structure and morphology of the prepared Sb2Te3 QDs were performed. The optical properties of Sb2Te3 QDs were studied using UV-Vis, PL and PLE. It is found that the average particle size of the prepared Sb2Te3 QDs is 2.3 nm, and the average height is 1.9 nm, with a good dispersive particle size uniformity, the PL and PLE peaks have a redshift, both PL and PLE are dependent on the excitation wavelength and emission wavelength. It is also found that Sb2Te3 QDs has obvious absorption and photoluminescence in the infrared band. The results indicate that the ultrasonic exfoliation method is feasible to prepare Sb2Te3 QDs, the characteristics of the material show the potential application in infrared detector.
2020, 49(1): 0103003.
doi: 10.3788/IRLA202049.0103003
Graphene has some unique properties, such as ultra-high carrier mobility, zero band gap, broadband response, which make it a promising material in infrared photodetection. In this review, the development history of graphene-based infrared detectors was analyzed, and the mechanism of relevant photoelectric response was summarized. The responsivity, wave-band, response speed and device structure were sorted out. The challenges of material preparation and process compatibility of graphene-based detectors were also discussed and prospected.
2020, 49(1): 0103004.
doi: 10.3788/IRLA202049.0103004
Germanium (Ge) is considered as one of the most promising materials for near infrared (NIR) photodetectors, due to its large absorption coefficient at NIR wavelengths, high carrier mobilities, and process compatibility with silicon (Si) architecture. Focusing on the challenges of Ge NIR photodetectors, in this paper, the progress of Ge materials and technologies for photodetectors in our group was reviewed extensively. Firstly, the preparation process of Si-based Ge materials was introduced, in which high crystal quality Si-based Ge materials were fabricated by a two-step epitaxy method, Ge/Si wafer bonding, and Ge condensation techniques, respectively. Then the n-type doping technology of Ge was studied, in which high n-type doping concentrations and shallow junctions of Ge materials were prepared by two-step annealing (low temperature pre-annealing and excimer laser annealing) for phosphorus-implanted Ge substrate and spin-on doping of phosphorus on Ge substrate, respectively. Finally, the modulation of Schottky barrier height of metal/Ge contacts were studied, and a high-performance Ge Schottky photodetector was prepared by combining ITO transparent electrode and ultra-thin metal film interlayer.
2020, 49(1): 0103005.
doi: 10.3788/IRLA202049.0103005
The avalanche photodiode detector based on InGaAs/InP has a working response band range of 0.9-1.67 μm, which has high detection efficiency and single photonic sensitivity in Geiger mode. By configuring different bias circuits, it can work in gating and free running mode. At present, the gating mode is mainly used, and can be applied to quantum key distribution with known arrival time of photons. In laser ranging, lidar imaging and other applications, when the arrival time of photons is unknown, the device needs to work in free running mode. Through internal integration or on-chip integration of self-quenching devices, the detector itself has the function of self-quenching or self-recovery, does not need external quenching circuit, and can work in free running mode. This greatly expands the application field of InGaAs/InP single-photonic detector, and has the advantage of fabricating single-photonic detector array at the same time. In addition, the cutoff wavelength of the detector can be further extended to 2.4 μm by using InGaAs/GaAsSb II superlattice material as the absorption layer of the avalanche photodiode. In this paper, the Geiger mode APD was introduced, and the principle and performance of the current free running mode and the extended wavelength inp based single photonic detector were described in detail.
2020, 49(1): 0103006.
doi: 10.3788/IRLA202049.0103006
SWIR InGaAs FPAs are widely applied to space remote sensing, low light level night vision and medical diagnostics due to the high detectivity and uniformity. Highly sensitive NIR InGaAs FPAs with response covering from 0.9 μm to 1.7 μm, the extended SWIR InGaAs FPAs with the cutoff wavelengths from 1.0 μm to 2.5 μm, and other novel SWIR InGaAs FPAs have been studied respectively at Shanghai Institute of Technical Physics of Chinese Academy of Sciences over the past ten years. NIR InGaAs FPAs have developed from some typical linear 256×1, 512×1 FPAs to 2D format 320×256, 640×512, 4 000×128 and 1 280×1 024 FPAs. Typically, the dark current density was about 5 nA/cm2 and the peak detectivity was superior to 5×1012 cm·Hz1/2/W at room temperature. 2D format 1 024×256, 1 024×512 extended wavelength InGaAs FPAs with high frame rate were also developed for the hyperspectral applications at SITP. The dark current density drops to 10 nA/cm2 and peak detectivity was over 5×1012 cm·Hz1/2/W at 200 K. By using novel epitaxial materials and the light trapping structures, the visible-NIR InGaAs FPAs for wavelength band of 0.4-1.7 μm have also been developed. The as-prepared 320×256, 640×512 InGaAs FPAs were obtained with quantum efficiency superior to 40%@0.5 m, 80%@0.8 m and 90%@1.55 m. For polarimetric detecting, InGaAs devices integrated with sub-wavelength metal grating of different angles (0°, 45°, 90°, 135°) have been developed, which exhibit the extinction ratio of greater than 20:1.
2020, 49(1): 0103007.
doi: 10.3788/IRLA202049.0103007
New infrared devices prepared by InAs/GaSb superlattice materials have developed rapidly in the last decade. The paper carries out practical researches on mid-/short-wavelength dual-color infrared detector based on type-II InAs/GaSb superlattice. Firstly, a mid-/short-wavelength dual-color chip structure was designed based on two back-to-back n-i-p junctions. Then the PNP superlattice material with complete structure, smooth surface and low defect density was grown by molecular beam epitaxy. Finally, 320×256 focal plane arrays with excellent performance was fabricated and measured. The RA value of middle-wave channel reached 26 kΩ·cm2 and the short-wave channel reached 562 kΩ·cm2 at 77 K. The spectral response indicated the short-wave response band of 1.7-3 μm and the middle-wave of 3-5 μm. The middle-wave channel exhibits a detectivity value of 3.12×1011 cm·Hz1/2W-1, a photo-response non-uniformity of 9.9% and an effective pixel rate of 98.46%, while the short-wave channel exhibits a detectivity value of 1.34×1011 cm·Hz1/2W-1, a photo-response non-uniformity of 9.7% and an effective pixel rate of 98.06%.
2020, 49(1): 0103008.
doi: 10.3788/IRLA202049.0103008
640×512 Quantum Well Infrared Photo-detector(QWIP) long wavelength infrared(LWIR) focal plane arrays(FPA) were made by using GaAs/AlGaAs quantum well structure. The response spectra were at 10.55 μm. Integrated with rotation sterling cooler which gave a temperature of 50 K, the FPA was measured to find the results that NETD was about 22.5 mK. The FPA assembly kept good performance after the switch-on-off cycling test and thermal vacuum test. The illumination non-uniformity of the focal plane with a cold shield was calculated with a numerical method. The results were compared with the approximate analytic method. It is shown that numerical method should be used for small F-numbers. Thus, the measured non-uniformity is believed to be dominated by the illumination non-uniformity. By using the MEEP FDTD software, calculation about the near-field photo-coupled electrical-field energy were designed and results show that current QWIP structure parameters are near optimized in term of optical diffraction.
2020, 49(1): 0103009.
doi: 10.3788/IRLA202049.0103009
It's the trend of information technology development that infrared focal plane array (FPA) outputs digital signal directly, the critical technique is the digital readout integrated circuit (ROIC). The architecture of digital ROIC was introduced in this paper after the summary of related research status. The sources and influence of temporal noise and spatial noise were analyzed in detail, then the design guide for low noise was also shown. In addition, two digital ROICs were designed based on the discussion of linearity, dynamic range and frame rate. The first ROIC was implemented with column-level ADCs, which was used for 640×512 digital FPA. The measurement results show that the readout noise of ROIC is 150 μV, and the NETD with mid-wave infrared detectors is 13 mK. Digital pixel architecture is used for the second ROIC, which is connected to 384×288 long-wave infrared FPA. The measured NETD is less than 4 mK, and the dynamic range is larger than 90 dB. The max frame rate achieves 1 000 Hz. The two ROIC prototypes effectively improve the sensitivity, dynamic range and frame rate of infrared FPA, which confirms the advantages of digital ROIC technology to the performance development of infrared detectors.
2020, 49(1): 0103010.
doi: 10.3788/IRLA202049.0103010
The applications of the second HgCdTe Infrared Focal Plane Arrays(IRFPA) have exploded in the past 10 years, meanwhile the third IRFPA has developed rapidly. This article makes a brief retrospect in development of HgCdTe IRFPA detector, combines with applications of HgCdTe IRFPA detector, summarizes the research works and the engineering applications of HgCdTe IRFPA detector and looks forward to the further development of HgCdTe IRFPA detector.
2020, 49(1): 0103011.
doi: 10.3788/IRLA202049.0103011
The key to realize very high sensitivity infrared detector is to obtain as much charge storage capacity as possible in the limited pixel area of readout circuit. The pixel-level ADC based on pulse frequency modulation is the main method to realize the readout circuit of very sensitive infrared detector. The principle of pixel-level pulse frequency modulation ADC was described. The progress of pixel-level digital readout circuit in MIT Lincoln Laboratory of the USA and CEA-LETI of France were introduced. As a new technology of expanding circuit density from three-dimensional space, the progress of 3D readout circuit was introduced. Finally, the development of readout circuit for very high sensitivity infrared detector in Kunming Institute of Physics was introduced. Using pixel-level ADC technology and digital domain TDI technology, the long-wave 512×8 digital TDI infrared detector assembly was developed by Kunming Institute of Physics with the peak sensitivity of 1.5 mK.
2020, 49(1): 0104001.
doi: 10.3788/IRLA202049.0104001
Cryocooler is an important equipment to provide low temperature working environment for infrared device. However, its driving system's conducted interference severely affects the precision of the infrared loading. It's not easy to analyze the common-mode part included in conducted interference. To study the common-mode interference mechanism, based on an existing infrared system project's cryocooler and its driving system, the mechanism was quantitatively analyzd using a new multi-physics co-simulation method and the model's accuracy was verified by specific experiment measurement. Finally, the characteristic of disturbance pathway and source were analyzed and the mechanism of the common-mode interference was concluded. Results show that, the parasitic parameter of the cryocooler is the most important factor of transmission path within the range of test frequency. However, with frequency increase, the effect of cable's parasitic parameter is increasing and can't be ignored. The interference mechanism concludes that the common mode interference produced by system may induce the overrun of the CE102 standard from 500 kHz to 1 MHz.
2020, 49(1): 0104002.
doi: 10.3788/IRLA202049.0104002
Due to the influence of infrared focal plane arrays production technology and material characteristics, blind pixels are inevitable in infrared focal plane arrays, which seriously affects the processing and application of infrared data. The push-broom thermal infrared hyperspectral imager which using grating system generally takes one dimension of the infrared focal plane arrays as the spectral dimension and the other dimension as the spatial dimension, which is quite different from the imaging mechanism of the thermal imager with two spatial dimensions. Conventional laboratory calibration and scene detection methods based on moving window cannot meet the requirements of blind pixel detection on the thermal infrared hyperspectral imager. A new blind pixel detection algorithm based on spectral angle matching was proposed to detect the blind pixels in thermal infrared hyperspectral imager. Taken spectral dimension information into account, this method generated temperature rise spectrum data from blackbody calibration data at different temperatures. Based on the basis of data regularization processing, the pseudo-spectral curve of effective pixels were extracted automatically, and the blind pixels were detected automatically by means of spectral angle matching. To validated the new blind pixel detection algorithm, a typical thermal infrared hyperspectral imager was used to collect image data and detecte the blind pixels of the imager. The results indicates that this method makes full use of spectral information of the thermal infrared hyperspectral imager and has high detection accuracy. The data after blind pixels compensation can satisfy the application of thermal infrared hyperspectral data.
2020, 49(1): 0104003.
doi: 10.3788/IRLA202049.0104003
When the rocket engine is working in high vacuum environment, the gas jet expands rapidly under the condition of extremely low back pressure, forming the vacuum plume. This vacuum plume can produce impact and erosion on space targets, and its infrared radiation characteristics can be widely used for the detection and recognition of the space targets. Based on the theoretical model of collisionless free molecular flow, the rapid analytical calculation of vacuum plume was carried out in this paper. The expansion and diffusion characteristics of the plume were obtained, which accorded with the known flow rule. On the basis of the calculated plume flow parameters, the Voigt line function was used to describe the dilating of the rarefied gas, and the radiation characteristics were calculated by line-by-line and LOS method. The results show that the boundary and diffusion distribution of vacuum plume are determined by the speed ratio of the nozzle exit. The stronger exit speed ratio is, the greater the area of the plume diffusions, and the higher the normalized density and temperature on the axis are. When the temperature of the nozzle exit is same, the radiation intensity of the plume increases with the increase of exit speed ratio. However, when the speed of the nozzle is same, the radiation intensity of the plume decreases with the increase of exit speed ratio. In the case of the same exit speed ratio, the radiation intensity is positively correlated with the thrust.
2020, 49(1): 0104004.
doi: 10.3788/IRLA202049.0104004
For the stealth effect evaluation of a single infrared image, it is necessary to consider the image similar feature information reflected by the pixels in the image. A single similarity measurement method cannot fully and accurately reflect the similarity between infrared images. On the basis of equally dividing a single infrared image, the advantages of four similarity measurements based on image gray histogram method, direction gradient histogram feature method, structural similarity method and target classification were considered comprehensively. The principal component analysis method was used to determine the weight values of different similarity measurements, and an evaluation method based on comprehensive similarity measurement was proposed. Through the comparison of horizontal and vertical experiments between the similarity measurement methods, the mean and standard deviation of each similarity measurement between the target and the background image for different occlusion situations was analyzed. The results show that the comprehensive similarity measurment can more accurately reflect the similarity information between images, the problem of single-infrared image stealth effect evaluation is more effectively processed.
2020, 49(1): 0105001.
doi: 10.3788/IRLA202049.0105001
To realize the rapidly tunable output of grating line selectable 9-11 μm CO2 laser, two direct-drive AC servo motors were used to drive high speed rotation and precise orientation of the grating. In the experiment, the switching time of laser lines was less than 100 μs under dual optical path mode, and the switching time of the laser line was less than 50 ms under single optical path mode. The output spectrum of laser contained 70 lines, in which the output pulse energy of 9P(20) and 9P(28) were above 100 mJ, the output pulse energy of 9R(30) and 9P(40) were above 90 mJ. The laser pulse width was shorter than 100 ns, and the repetition rate was 20 Hz.
2020, 49(1): 0105002.
doi: 10.3788/IRLA202049.0105002
To achieve the ultra-spectral detection of atmospheric trace gases in both nadir and limb, the time-modulated Fourier transform spectrometer was used to obtain the spectral information, and the optical path scanning speed stability satisfied greater or equal to 99.5%. In this paper, a control system of the translational scanning interferometer was investigated and the system principle diagram was presented. Considering the long-range optical path distance (OPD) and high scanning speed stability requirements, a interferometer control system of the translational optical path scanning was applied, and the schematic diagram of the scanning implementation was given. As the fluctuation of scanning speed caused by frictions, mechanical vibrations and other disturbances, its influence on the interference signal intensity and inversion spectrum was theoretically analyzed. The motion of OPD scanning and the interference have a characteristic of periodicity, this paper proposed a plug-in repetitive controller, which has an excellent in suppressing periodic disturbances, and implements uniform scanning. MATLAB numerical simulation and experimental verification were carried out for the control strategy, the results indicate that the plugin repetitive controller can improve the speed stability periodically. When the angular mirror moves at 10.625 mm/s, the final displacement error is about ±0.000 25 mm, and the velocity error is about ±0.000 4 mm/s, which meet the performance requirements.
2020, 49(1): 0105003.
doi: 10.3788/IRLA202049.0105003
We conducted ground-based optical observations on a group of satellites used for radar calibration, whose main parts were aluminum balls. Our observations verified their luminosity changes and spectral characteristics were simple, and it was easy to carry out analyses on the factors which affected luminosity and spectral characteristics. The simulation measurement in the laboratory for the aluminum ball also shows its characteristics of good isotropicity, stable reflective and spectral characteristics. Based on the measurement results, we constructed the luminosity calculation model for the aluminum-ball satellite. Comparing with the measured results, we found that the characteristics of the material and shape characteristics of the aluminum ball can simplify the satellite photometric calculation model to the greatest extent. Moreover, the methods of the measurement and the luminosity calculation model construction were also proved to be correct, enabling the real-time satellite luminosity calculation, which can be applied to the dynamic flux calibration and the calibration of the detection capability under fast and variable-speed motion of space-based and ground-based optical detection equipment.
2020, 49(1): 0105004.
doi: 10.3788/IRLA202049.0105004
Laser imaging radar can obtain point cloud data reflecting the three-dimensional position of the target, directly estimate the three-dimensional attitude angle of the target, and is an important parameter for feature extraction and target registration. To realize the three-dimensional attitude estimation of scenes, an optimized three-dimensional attitude estimation algorithm(OPDVA) based on point normal vector (PDVA) was proposed to solve the problem of large deviation of the positive vector representing the coordinate axis of scene coordinate system(SCS) in real scenes. In this method, remove point normal vectors in other directions in the cluster by RANdom SAmple Consensus (RANSAC) plane model was removed, and the corresponding normal vectors of the optimal fitting plane were the revised SCS coordinate axes. Using rotational transformation and resampling techniques, 3 groups of real scene range image were experimented with rectangular bounding box method, PDVA and OPDVA respectively. The experimental results show that the OPDVA method is superior to the other two methods in pose estimation. The error of pose estimation does not exceed 4°, and it is also suitable for occlusion scenarios.
In this study an innovative peg-nail structured laser modification was carried out double-ceramic-layer thermal barrier coating (DCL-TBCs) by a pulsed Nd:YAG laser which were fabricated by a NiCoCrAlYTa bond coat and two ceramic top coat (YSZ and La2Ce2O7, LC) sprayed by air plasma spraying. Results indicate that the roughness of the laser modified surface has significantly improved, compared with as-sprayed coatings. The completely recrystallization can be found in the peg-nail structured laser modified unit, including a fully dense columnar microstructure. Due to the peg-nail structured laser modification which generated re-melting and resolidificating at the whole LC coat and partial YSZ coat, can greatly improve the interface bonding property and the bonding strength, the peg-nail structured laser modified samples have better spallation or delamination resistance than the normal as-sprayed DCL-TBCs.
2020, 49(1): 0105006.
doi: 10.3788/IRLA202049.0105006
In order to study the scattering intensity and polarization characteristics of the bubble curtain illuminated by laser in the wake, a Monte Carlo model based on the propagation of polarized light was used. A simulation of the 3D distribution pattern of water with a group of bubbles incident on it by a polarized laser beam was presented. The scattering intensity and polarization state of bubbles and bubble groups at different bubble scales and different scattering angles were studied, and the influence of bubble number density and thickness on scattering intensity and polarization state was analyzed. The results show that the intensity and polarization of the scattered light are sensitive to the bubble size and the scattering angle. The larger the bubble size is, the more the scattering intensity and polarization tend to be concentrated in the small angle scattering in the transmission direction. With the increase of the number density and thickness of the bubble curtain, the sensitivity of the intensity of the scattered light decreases with the change of the scattering angle, and the depolarization effect increases.
The diaminodikhunophenoxy chloride indium phthalocyanine (Pc) was covalently bonded with carboxylated GO (GO-COOH) to obtain the diaminodikhunophenoxy chloride indium phthalocyanine-graphene oxide (Pc-GO-COOH), and the bonding products as raw material of the reaction initiator. Four kinds of polymer samples with different molecular weight were obtained by atom transfer radical polymerization (ATRP) with methyl methacrylate (MMA) as polymerization monomer. The molecular weight and molecular weight distribution of the prepared polymers were tested by gel permeation chromatography (GPC). The test results show that the preparation of polymers has narrow molecular weight distribution, the polymer reaction presents good controllability. The results of third-order nonlinear optical properties test on polymer sample solution by Z-scan show that the preparation of polymer has excellent third-order nonlinear optical properties, and when the molecular weight of polymer, respectively 9 063 and 12 196, the third order nonlinear polarizability values are 8.1×10-11 esu and 2.1×10-11 esu. At the same time, the optical limiting performance test show the effective excitation and ground state absorption cross section ratios of the two samples are 2.69 and 2.20, respectively. It has a good limiting ability and a great application prospect.
2020, 49(1): 0113001.
doi: 10.3788/IRLA202049.0113001
Ф1.3 m concave ellipsoid reflector is the primary mirror of a remote sensor optical system, and its centering accuracy is demanding. Because the reflector had large aperture and long curvature radius of the vertex, it is difficult to center by centering instrument method, and the accuracy was low. By analyzing the compensating phenomena between the two kinds of off-center of aspheric surface, it could be seen that the accuracy of contact measurement centering by laser tracker was only 0.15°. The accuracy of contact measurement centering by three-coordinate instrument measuring instrument can reach 0.005°, but its range was limited, and repeated handling in optical processing will cause inconvenience. The Offner zero compensation test was used to verify the optical path for interference centering. The interference method converts the eccentricity of the mirror into the primary aberration of the detection system wavefront, which can also achieve an accuracy of 0.005°. The error source of this method was mainly the focus position error of interferometer, which was a systematic error. It could be eliminated by multiple centering measurements with rotating mirrors. The maximum deviation of off-center was only 0.023 mm and 0.002°, compared with the results measured by the three-coordinate instrument. The in-situ centering measurement of large aperture concave aspheric mirror was realized.
2020, 49(1): 0113002.
doi: 10.3788/IRLA202049.0113002
In tunable diode laser absorption spectroscopy technology, the direct absorption method can directly obtain absorption line profile function through fitting the transmitting light intensity. But at present, the wavelength modulation method with higher signal-to-noise ratio can't measure it effectively. A measurement theory and method of absorption line profile function based on multiple harmonics was proposed. Through the analysis of harmonic expressions, the ratio between the 2nd harmonic and 4th harmonic at the center frequency was only related to the absorption line profile function and modulation index. When the modulation index m was 2.492 8, the ratio between the 2nd harmonic and 4th harmonic was fixed to 2.186 2 no matter what the ratio of Gauss linewidth and Lorentz linewidth was. According to the characteristics of this point, the spectral line half width can be obtained firstly, and then it can be applied in 2f/1f calibration-free measurement of gas concentration. In the experiment, CO concentration has been measured using 2 326.82 nm spectral line through the proposed method. The error between the proposed method and traditional direct absorption method was less than 2%. An important theoretical basis for the measurement of absorption line profile function in wavelength modulation method has been provided by this proposed method, and the traditional theory of 2f/1f calibration-free method has been further improved.
2020, 49(1): 0113003.
doi: 10.3788/IRLA202049.0113003
In order to accurately and reliably measure the flying speed of the fragment in any horizontal direction in the static detonation test, a method for measuring the flying speed of the static detonation fragment based on active screen array was proposed. Firstly, twelve groups of active six-screen arrays were arranged around the static explosion point of measured ammunition. The flight parameters(such as velocity, incident angle and vertical target density) of these fragments can be obtained when they pass through the detection area in every six-screen arrays. Secondly, according to the configuration of the proposed screen array, its model was established to obtain the related flight parameters, and then the change rule of error with each velocity component was analyzed in a certain range. Through theoretical analysis and live ammunition experiment, results show that the component errors of fragment velocity is less than 2.7 m/s, and thus the proposed method can meet the measurement requirement of fragment velocity in any horizontal direction.
2020, 49(1): 0113004.
doi: 10.3788/IRLA202049.0113004
3D measurement of structured light technology is an extremely vital approach to obtain 3D information of objects. Extraction of the centerline of laser stripe is a key factor that could affect the accuracy and speed of 3D measurement of structured light in the meantime. A method of extracting centerline of laser stripe for 3D measurement of structured light that adaptive to multiple scenarios was proposed. The adaptive convolution template was generated by making full use of the geometric information and correlation of laser stripe in the image, which can filter and enhance the image quality of laser stripe and enable the gray value of cross-section of laser stripe satisfy the Gauss distribution. The sub-pixel accurate localization and extraction of laser stripe centerline were realized by gray weighted algorithm. The experimental results show that the proposed adaptive convolutional algorithm can extract the laser stripe centerlines of the objects with different shapes and materials based on multi-scenarios and overcome the influence of uneven brightness and noise at the same time. Based on the algorithm, the extraction time of single frame is shortened to 0.107 s and the relative error is reduced to 0.076 5%, which improves the extraction accuracy and speed of laser stripe centerline effectively.
2020, 49(1): 0113005.
doi: 10.3788/IRLA202049.0113005
Deep space probes have limited power consumption and volume, and have diverse mission conditions. Compared with low-orbit earth probes, deep space probes have higher requirements for the mission capabilities of navigation sensors. This paper proposed a fast pose measurement and ground object recognition technology based on time-of-flight imaging. In order to meet the time requirements of pose measurement under the premise of ensuring the accuracy of pose measurement, a dynamic scale estimation method based on depth information was proposed. This method improved the temporal stability of point cloud registration under multi-scale object-side changes. The average registration time was reduced by more than 60% and the average registration accuracy was about 0.04 m. In order to meet the needs of multi-scale and multi-morph object recognition, a light-weight deep neural network was used to detect ground objects based on scene depth information. The results show that this method can quickly perceive the features of ground features, and the accuracy rate is more than 70% in real scenes.
2020, 49(1): 0114001.
doi: 10.3788/IRLA202049.0114001
In order to meet the structure positioning accuracy requirements of the telescope secondary mirror, a fixed length rod end axial translational motion model of hexapod was proposed. From the point of view of differential geometry, the nonlinear kinematics between the input joint space vector and the output workspace vector of the mechanism was studied, and the curvature concept was used to measure the nonlinear bending of the trajectory. Comparing with the Jacobian matrix, it was found that the curvature of the parallel mechanism was consistent with the instantaneous linear property reflected by the Jacobian matrix. The maximum nonlinearity error of the designed secondary mirror parallel adjustment mechanism was about 3.15 μm in the whole motion range. The test results show that after the polynomial error curve fitting correction, the three-dimensional translational repeating positioning accuracy of the secondary mirror adjustment mechanism is less than 2.6 μm, and the two-dimensional rotation repeat positioning accuracy is less than 1.8″, which meet the needs of actual telescope observation. At the same time, the curvature metric method can also provide a new idea for the nonlinear analysis and correction of other parallel mechanisms.
2020, 49(1): 0114002.
doi: 10.3788/IRLA202049.0114002
To solve the problem that the large field of view and high resolution of the traditional imaging system can not be achieved simultaneously, a large field of view curved bionic compound eye optical system was designed. Firstly, aiming at the arrangement of the spaced-type circumferential layered micro-lens array, a mathematical model of the imaging principle of the curved bionic compound eye optical system was established. The imaging scheme that combining the microlens array and the transferring image system was proposed to solve the matching problem of curved surface image which formed by the micro-lens array and the planar detector; and optical design software was used for simulation and tolerance analysis. The designed curved bionic compound eye optical system has a total field of view of 152°, a combined focal length of 61.14 mm, an angular resolution of 2.304″, and a total length of 16.39 mm. Compared with the traditional large field of view imaging system, the curved bionic compound eye imaging system has smaller distortion and higher resolution.
2020, 49(1): 0114003.
doi: 10.3788/IRLA202049.0114003
Because micro-light remote sensing can detect ground objects under low illumination conditions such as nighttime and twilight, this remote sensing camera uses micro-light remote sensing to complement the traditional visible light remote sensing to achieve observation in visible light all-day long. Considering the system's long focal length(500 mm), large field of view(5°×2°),large relative aperture(F number 3.8),miniaturization and high optical efficiency, this remote sensing camera used off-axis three-mirror system structure and common light path for double detectors, subfield of view to achieve simultaneous imaging from micro-light and visible light detectors. The optical system design and imaging quality of the optical system of the camera were analyzed in detail. The results show that the modulation transform function (MTF) of traditional visible light fields of view are more than 0.4 at the Nyquist frequency of 200 lp/mm and the MTF of micro-light fields of view are more than 0.75 at the Nyquist frequency of 77 lp/mm and the MTF is close to the diffraction limits. Based on development and launch processes of optical load, system tolerances were analyzed from the four processed of machining, alignment, primary focusing and non-focusing, and the result of tolerant assignment was given. In addition, the extensibility of the optical system was illustrated.
2020, 49(1): 0116001.
doi: 10.3788/IRLA202049.0116001
To resolve separated viewing zones, a one-dimensional dual-view integral imaging three-dimensional (3D) display based on a polarizer parallax barrier was proposed. The imaging model of the one-dimensional dual-view integral imaging 3D display based on the polarizer parallax barrier was established. The principle of the one-dimensional dual-view integral imaging 3D display was illustrated in detail. The calculation formulas of the width of the viewing zone and the viewing angle were deduced by using geometrical optics. A test equipment of the one-dimensional dual-view integral imaging 3D display was developed. By using left and right polarizer parallax barriers, two different 3D images were viewed from 18° to the left and the right in the same viewing zone.
2020, 49(1): 0116002.
doi: 10.3788/IRLA202049.0116002
Based on convection-diffusion effect, a fluid lens with optical gradient refractive index microcavity was established by using finite element method. The stable concentration distribution of the core and cladding liquid after convenction-diffusion process was analyzed, which was called refractive index distribution of mixed fluid. The structure of convection-diffusion model was studied. For gradient refraction index characteristics of optical microfluidic tunable lens, the effects of different cross-sections on the stability of refractive index distribution along the direction of fluid flow direction were studied respectively in general(the refractive index of core fluid was larger than that of cladding fluid) and in the case of central depression(the refractive index of core fluid was smaller than that of cladding fluid).
2020, 49(1): 0118001.
doi: 10.3788/IRLA202049.0118001
Based on slot waveguide structures, a polymer-based microring operating at around 890 nm wavelength was proposed and designed. A detailed analysis of modal characteristics of the slot waveguides were carried out from refractive index sensing. The relationships between the sensitivity and the waveguide height, width and slot width were analyzed. Conventional bend slot waveguide had a large propagation loss, which had a bad influence on the quality factor Q and the extinction ration of the microring. An asymmetric slot waveguide was designed which could make the mode propagate in the middle of the waveguide and then decrease the bending loss. A strip-slot mode converter based on multimode interference (MMI) structure was designed for better coupling between strip and slot waveguides. Simulations show that the sensitivity of the designed microring resonator could reach 109 nm/RIU.
2020, 49(1): 0126001.
doi: 10.3788/IRLA202049.0126001
Under the complicated sea and sky background, the existing infrared small target detection algorithms have the problem of high false alarm rate. In this paper, the feature differences between the target and the background were deeply analyzed. Firstly, a method based on gray difference and gradient direction consistency was proposed. The small target was enhanced and some background clutter was suppressed. Secondly, the sharp edge background was further suppressed by combining the eigendecomposition method. Finally, the adaptive threshold was used to separate the small target. The experimental results show that compared with the five existing algorithms, the proposed detection algorithm can effectively reduce the false alarm rate in different complex scenes, greatly improve the signal-to-clutter ratio (SCR) and the background inhibitory factor (BSF), and have good robustness.
2020, 49(1): 0126002.
doi: 10.3788/IRLA202049.0126002
In order to enhance the detection and recognition performance of the terminal sensitive missile on the ground armor target in different scenarios, the application background of the terminal sensitive missile-loaded linear array laser radar was fully considered, and the integrated cross-scan line method and the ground-distance image point of the gradient connected domain were proposed. Cloud segmentation algorithm was used to improve the segmentation effect on the ground and target image. Firstly, the original distance information obtained by laser radar scanning was converted into the horizontal ground height value, and the spatial slope was transformed into the horizontal plane by the cross-scanning line method to enhance the adaptability on different terrains. Then, the ground point cloud connected domain algorithm was used to extract the ground. Point cloud and morphological gradient threshold method were used to segment the target point cloud. Finally, the geometric similarity of the feature segmentation effect was calculated. The experimental results show that the proposed algorithm has good applicability to various terrains such as positive slope and side slope. It can accurately and effectively segment the point cloud in different heights, terrains and slopes, and improve the target recognition performance of terminal sensitive missile.
2020, 49(1): 0126003.
doi: 10.3788/IRLA202049.0126003
In order to meet the long-term tracking requirements of platforms with weak computing power, such as the embedded system with C64x+ DSP as the computing core, a long-term tracking algorithm with low time complexity was proposed, which consisted of two parts. One part was the continuous tracking part and the other part was the target detection part. The continuous tracking part was based on adaptive update spatio-temporal context algorithm(STC), and the target detection part used normalized cross-correlation matching algorithm. If there were no special tracking scenarios such as field of view and fast moving target, the continuous tracking part outputted tracking results. After tracking failure, the whole image was processed in the target detection part, and the target was re-locked as long as the target appeared in the image again. Experiments show that target detection can accurately detect the target after it appeared, which meets the requirements of long-term tracking. At the same time, the robust of continuous tracking is also improved because the target location is redefined by the target detection part, when the result is not reliable. Using OTB2013 data set to test, the accuracy of this algorithm is 4.95% higher than that of STC algorithm.
