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2021 Vol. 43, No. 12

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Survey & Review
Research Progress of Graphene Heterojunctions and Their Optoelectronic Devices
HAN Tianliang, TANG Libin, ZUO Wenbin, JI Rongbin, XIANG Jinzhong
2021, 43(12): 1141-1157.
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Abstract:
Graphene is a two-dimensional material with high mobility, high thermal conductivity, high transmittance, large specific surface area, and good mechanical strength. It is widely utilized as a transparent electrode and charge-transporting layer in optoelectronic devices. However, graphene is a zero-bandgap material with inherent semi-metallic properties that limit its application in the field of semiconductor optoelectronic devices. The construction of heterojunctions has become a critical means to meet the requirements of semiconductor applications in specific industries. To date, many different graphene heterojunction structures have been reported owing to the wide selection of heterojunction materials. Based on the properties of graphene, this study describes the development and preparation methods of graphene heterojunctions and summarizes the research progress of photoelectronic devices based on graphene heterojunctions from the perspective of material preparation and device structure. Lastly, the development of graphene heterojunctions in optoelectronic devices is discussed.
Special Column: Infrared Optical Systems
Distance Estimation for Precise Object Recognition Considering Geometric Distortion of Wide-angle Lens
LIU Guangwei, CAI Yi, CHEN Dongqi, WANG Lingxue
2021, 43(12): 1158-1165.
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Face and license plate recognition are crucial aspects in the field of intelligent security. A high-spatial-resolution imaging system with a large-format detector and low-distortion optical lens is required for recognizing small-scale features and rich details in faces and license plates. However, security systems need to monitor wide area, which requires a wide-angle lens with a wide field of view, but with some distortion. Therefore, precise target recognition should be used as a constraint to balance the high spatial resolution and wide field of view when designing an imaging system that can recognize details and monitor a wide area. Under such application requirements, an evaluation index based on pixel areal density is proposed. With the aid of this evaluation index, a distance estimation method for precise object recognition, considering the radial distortion of the wide-angle lens, was designed. Rotated and translated faces and license plates were used to demonstrate the estimation method. The results indicate that the recognition distance with radial distortion is less than that without radial distortion. When the translation distance is 1 m and 2 m, the difference between the actual recognition distance and the ideal recognition distance is 34.2% and 27.5%, respectively.
Design of Cooled Medium/Long Wave Infrared Dual-band Integrated Reflective Optical System
LIU Fangfang, ZHAO Jian, CONG Qiang, LI Tuotuo, TANG Tianjin, WU Jun
2021, 43(12): 1166-1171.
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Abstract:
A three-mirror anastigmatic(TMA) optical system was adopted to prevent chromatic aberration of the refractive system by adding a dichroic beam splitter behind the tertiary mirror to simultaneously implement the image to the MWIR and LWIR detectors. The integrated system included three off-axis mirrors and a dichroic beams plitter. The surface of the tertiary mirror was an XY polynomial freeform surface that could correct system aberrations. The structure of the system was re-imaged with 100% cold shield efficiency. The F-number was 2.67, the full field of view(FOV) was 11.4°×1.8°, the working band is 3.55-3.93 μm for the MWIR channel and 10.3-12.5 μm for the LWIR channel. The modulation transfer function (MTF) average values of MWIR were greater than 0.5 at 25 lp/mm, and the MTF average values of the LWIR were greater than 0.4 at 12.5 lp/mm. The temperature compensation of the optical system was optical passive athermalization. The temperature range was -40℃ to +60℃.
Structural Design and Support Characteristics Analysis of Cryogenic Mirror Assembly
SHEN Kai, HE Xin, ZHANG Xingxiang
2021, 43(12): 1172-1176.
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Abstract:
The infrared opto-mechanical system can improve detection sensitivity by working in a cryogenic environment to reduce background radiation, which causes many technical challenges for mirror assembly structure design. In a cryogenic environment, different coefficient of thermal expansion (CTE) of the mirror and the connector cause the surface accuracy change to be the main problem. Design the structure of the ϕ450 mm mirror assembly working at 240 K. The mirror material is SiC, and the connector material is Invar. The support method is rear support in the center. Great flexibility is designed for the connector to improve surface accuracy. Further, the main design parameters are optimized and analyzed. The influence curves on the surface accuracy are obtained. The root mean square (RMS) of gravity along the optical axis is 8.585 nm, the RMS along the radial direction is 3.710 nm, and the RMS is 5.086 nm working at 240 K. The first order frequency is 277 Hz, and the lightweight rate is 89.4%.
Design of Airborne Miniaturized Middle Wavelength Infrared Continuous Zoom Optical System
WU Haiqing, WANG Weichao
2021, 43(12): 1177-1182.
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To satisfy the requirements of an airborne electro-optical system for miniaturized and lightweight optical system of an infrared thermograph, a 22× continuous zoom optical system of 30–660 mm was realized by combining front-end afocal extender and back-end continuous zoom optical system. The total optical length of the system was 244 mm, and the total length/maximum focal length ratio was 0.37. The system had a small optical length and large zoom ratio, which makes the system suitable for large airborne electro-optical pod systems for long-distance detection. Upon removing the front afocal extender, the back-end system could achieve a 22× continuous zoom optical system of 15 to 330 mm. The total optical length of the system was 138 mm, and the total length/maximum focal length ratio was 0.42. The system can be used as a continuous zoom optical system in small-and medium-sized airborne electro-optical pod systems for close-range target detection. The design results exhibit that the system can capture images effectively in both states: at the characteristic frequency of 33 lp/mm corresponding to the detector, all the MTF values of the central field view were approximately 0.3, close to the diffraction limit, all the MTF values of the 0.7 field view were approximately 0.2, and all the MTF values of the edge field view were approximately 0.15, which satisfies the application requirements.
Athermalization of Infrared Zoom Optical System with Large Relative Aperture
CHEN Xiao
2021, 43(12): 1183-1187.
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As the ambient temperature changes, the thermal defocus of optical lenses occurs in infrared lenses. The passive thermal design of an infrared prime lens can be realized by the combination of infrared materials and the introduction of a diffraction surface. However, most infrared zoom lenses are designed using active mechanical compensation. In this study, a passive athermalization design method for zoom optics is proposed based on the principles of zoom optical system and passive optical athermalization, and a long-wave infrared athermalization lens with a large relative aperture and dual field of view is achieved using this method. The focal length was 25/50 mm (with 2 zoom ratio), the wavelength band was 8–12μm, and the F number is 0.9. The system was based on a 640×512 uncooled infrared focal plane detector with a pixel size of 17 μm×17 μm. Three LWIR materials were used in the system, namely Ge, ZnSe, and HWS6, and three high-order aspheric surfaces were introduced to realize the athermalization zoom design. The final design exhibits good imaging quality and temperature applicability over a wide temperature range. In the temperature range of -50℃ to 80℃, the MTF is greater than 0.3 at 30 lp/mm. The system structure is simple, has good usability, and has broad application prospects in the field of infrared vehicles.
Low Temperature Evaluation Method of Infrared Detector Integrated with Optical System
ZHANG Lu, ZHANG Lei, FU Zhikai, TIAN Ya
2021, 43(12): 1188-1192.
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To test the low temperature MTF of infrared detectors integrated with an optical system inside a Dewar, a shell structure Dewar was designed. The inconvenient factors caused by the large size and complexity of the optical system is eliminated. The MTF test optical path was built to obtain the temperature distribution gradient of the integrated optical lens group, providing reliable data for the assembly accuracy and optical performance of the integrated optical lens group.
Design of a 3.7~4.8 μm Catadioptric Secondary Imaging MWIR Optical System
LI Zhuo, YE Zongmin, SUN Baojie, LIU Wenpeng
2021, 43(12): 1193-1196.
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Abstract:
The system is based on an RC structure to measure the optical characteristics of small targets and space targets. The initial structure of the reflective optical system was established by calculating the curve equation and the Gaussian formula. The re-imaging relay lens group was introduced into the structure of the system to realize the optimal design, which solves the problem of 100% cold diaphragm efficiency. The imaging quality was evaluated using Zemax, and a system with a focal length of 380 mm and a diameter of 200 mm is not only compact and simple, it also meets the actual measurement requirements.
Environmental Adaptability of Infrared Antireflection Films in Humid Hot Rain Forest
YANG Yuping, LIU Jian, ZHOU Xiaoyu, ZHAO Hongkun, LIU Yanfang, WANG Chongwen, ZHAO Yuanrong, GE Fan, XIAO Jianjun, LUO Rui, YANG Pinjie
2021, 43(12): 1197-1201.
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Abstract:
With the development of military infrared optical instruments, the requirements for the environmental performance of infrared optical coating elements are increasing. Antireflection films coated on Ge, ZnS, and ZnSe in the band of 8 to 12 μm are considered as the objects to study the environmental adaptability of infrared antireflection films to humid hot rain forest climate. The environmental adaptability is evaluated based on appearance, quality, and spectral transmittance, and the results are as follows: after three years of climate and environmental tests in hot and humid rain forest terrain, the infrared antireflection films are damaged, primarily through discoloration and delamination. With the extension of the test time, the discoloration becomes increasingly serious, and the discoloration area increases gradually. Initially, the mass decreases before increasing, and the spectral transmittance decreases slightly. The infrared antireflection films are invalid after three years of climate and environmental tests in hot and humid rain forests.
Materials & Devices
Thermal Stress Structural Optimization of InSb Infrared Focal Plane Array Detector
ZHANG Jiangfeng, DIAO Yunfei, ZHANG Xiaoling, MENG Qingduan
2021, 43(12): 1202-1206.
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Abstract:
In liquid nitrogen shock experiments, a thermal mismatch occurs owing to the difference in the linear expansion coefficients of the layered In antimonide infrared focal plane array detector, and the excessive thermal mismatch stress fractures the InSb chip. Based on the calculation theory of the thermal stress suitable for the elastic multilayer system, employing the design method of a balanced composite structure is considered to be effective in reducing the impact of the thermal mismatch on the InSb chip. Accordingly, we optimize the thermal strain on the upper surface of the balanced composite structure. In other words, the optimization involved making the thermal strain on the upper surface of the Readout circuit in the balanced composite structure as close as possible to the thermal strain on the lower surface of the InSb chip. Consequently, the reduced thermal mismatch reduces the thermal stress in the InSb chip. Considering the maturity of the device processing technology, the thickness of the readout circuit is set at 25 μm, which is the thinnest sheet of the readout circuit fabricated in our lab using the chemical mechanical polishing method. For the defined thickness (25 μm) of the readout circuit, the calculation results indicate that the thermal strain on the upper surface of the readout circuit is the closest to the thermal strain on the lower surface of the InSb chip. When these two structures are glued together by the underfill, the tensile stress accumulated in the InSb chip is the smallest. The significant reduction in the tensile stress in the InSb chip provides a reliable structural design scheme and an implementation approach to reduce the fragmentation probability of the InSb chip in the liquid nitrogen impact.
Study on the Effects of Yb: Ag Alloy Cathode on the Photoelectric Performance of the Top Emitting White Organic Light-emitting Devices
YANG Qiming, GAO Sibo, WANG Can, DUAN Liangfei, QIAN Fuli, DUAN Qian, ZHANG Jie, WANG Guanghua, LU Chaoyu, DUAN Yu
2021, 43(12): 1207-1211.
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Abstract:
Top-emitting white organic light-emitting diode(OLED) devices with a Mg: Ag alloy as a transparent cathode were fabricated. Based on the device structure of ITO/NPB: LiQ(5%) (10 nm)/TCTA(20 nm)/FIrpic+3.5% Ir(ppy)3+0.5%Ir(MDQ)2(acac) (25 nm)/TPBI(10 nm)/LiF(5 nm)/Yb: Ag (X%) (X nm), the top-emitting white OLED devices were prepared by using Yb: Ag alloy of different thickness as the cathode at the evaporation ratio of 10:1, the optimum thickness of Yb: Ag cathode was 12 nm by contrasting. The effect of different proportions of Yb: Ag alloy on OLEDs was investigated by changing the doping ratio of Ag. Based on the preliminary results, the alloy with a Ag mass fraction of 10% exhibits good electron injection characteristics, which can effectively improve the light-emitting characteristics of the device. When the current density was 20 mA/cm2, the driving voltage was 2.3 V, the brightness was 1406 cd/m2, and the color coordinates were close to (0.3407, 0.3922).
Image Processing & Simulation
Infrared and Visible Image Fusion Method Based on Improved Saliency Detection and Non-subsampled Shearlet Transform
YE Kuntao, LI Wen, SHU Leilei, LI Sheng
2021, 43(12): 1212-1221.
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Abstract:
To address the problems in the current infrared and visible image fusion method wherein targets are not prominent and contrast is low based on saliency detection, this paper proposes a fusion method by combining improved saliency detection and non-subsampled shearlet transform (NSST). First, the improved maximum symmetric surround algorithm is used to extract the saliency map of an infrared image, the improved gamma correction method is utilized to enhance the map, and the visible image is enhanced through homomorphic filtering. Second, the infrared and enhanced visible images are decomposed into low-and high-frequency parts through NSST, and the saliency map is used to guide the fusion of the low-frequency parts. Simultaneously, the rule of maximum region energy selection is used to guide the fusion of the high-frequency parts. Finally, the fusion image is reconstructed using the inverse NSST. The experimental results show that the proposed method is far superior to other seven fusion methods in terms of average gradient, information entropy, spatial frequency, and standard deviation. Thus, proposed method can effectively highlight the infrared target, improve the contrast and definition of fused images, and preserve rich background information of visible images.
Retinal Vessel Image Segmentation Based on RAU-net
ZHANG Lijuan, MEI Chang, LI Chaoran, ZHANG Run
2021, 43(12): 1222-1227,1233.
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Abstract:
In the diagnosis of ophthalmic diseases, segmentation of retinal blood vessels is a quite effective method. However, using this method, difficulties in blood vessel segmentation are often encountered due to the low contrast of the retinal blood vessel background and complex details of the blood vessel end. Thus, residual learning is introduced by adding a basic U-net network to the process of network design. Through the introduction of residual learning and attention mechanism modules into the basic U-net network in the process of network design, a new type of U-net-based RAU-net retinal blood vessel image segmentation algorithm is proposed. First, the residual module is added to the encoder stage of the network to address gradient explosion and disappearance caused by the deepening of the model network. Second, the attention gate module is introduced in the decoder stage of the network to suppress unnecessary features to ensure high accuracy of the model. Through verification of DRIVE, the accuracy, sensitivity, specificity, and F1-score of the algorithm reached 0.7832, 0.9815, 0.9568, and 0.8192, respectively. Thus, the segmentation effect was better than that of ordinary supervised learning algorithms
Ir Applications
Establishment and Verification of Multivariate Linear Regression Model for Prediction of Ethanol Concentration
XIAO Xiongliang, CHEN Changming
2021, 43(12): 1228-1233.
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Abstract:
A non-dispersive infrared absorption system comprising a light source, gas chamber, detector, and controller is designed, and multi-component gases of different concentrations (including ethanol, carbon dioxide, and water vapor) are injected into the chamber. An infrared spectrometer is used to collect the spectral data, and amulti-component gas mixture spectrum isobtained. A multiple linear regression model is established based on the regression coefficients of the dataset samples, and interference correction is performed to reduce the effect of carbon dioxide and water vapor on the concentration of ethanol. The established multiple linear regression model is evaluated, and the results indicate that the model is reliable and effective with a good linear regression effect. The model can be used to predict the gas concentration, and the prediction errors of ethanol, carbon dioxide, and water vapor concentration are within an acceptable range. The prediction error of ethanol concentration is the minimum, which is less than 2.0×10-4. The interference of carbon dioxide and water vapor can be mostly eliminated through interference correction. Importantly, the ethanol concentration can be predicted more accurately.

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