Journals >Infrared and Laser Engineering
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2024
Volume: 53 Issue 6
22 Article(s)
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[in Chinese]
Analysis and compensation of the influence of chromatic aberration on the imaging model parameters of star sensors
Yanzhao NIU, Xinguo WEI, and Jian LI
ObjectiveStar sensors serve as crucial tools for providing high-precision three-axis attitude information for various spacecraft, relying on stars as their reference points. To ensure the accuracy of star sensor attitude measurements, calibration is essential to obtain precise imaging model parameter values. However, sObjective Star sensors serve as crucial tools for providing high-precision three-axis attitude information for various spacecraft, relying on stars as their reference points. To ensure the accuracy of star sensor attitude measurements, calibration is essential to obtain precise imaging model parameter values. However, stars can be divided into different spectral types, each representing unique radiation characteristics. Current laboratory calibration methods commonly employ a single spectral band to simulate star imaging for parameter calibration, neglecting the spectral diversity of stars. Due to the disparity between the energy distribution of the single spectral band and the actual stellar spectral distribution, chromatic aberration leads to differences between the model parameter values obtained using the existing single spectral band calibration and the true values, thereby impacting on the accuracy of star sensor attitude measurement. Since complete elimination of lens chromatic aberration is unfeasible, this paper proposes a parameter compensation method for star sensor imaging models based on the spectral characteristics of stars. This approach aims to improve the accuracy of model parameters and reduce the impact of chromatic aberration on star vector measurement, thus improving the measurement accuracy of star sensors.Methods The article first establishes a star sensor imaging model under spectral differences, and further analyses how chromatic aberration affects the imaging model parameters for stars of varying spectral types. These analyses reveal that different spectral types of stars correspond to distinct imaging model parameters. Based on the established model mentioned and the theoretical analysis above, the article abandons the original method of simulating stellar imaging with a single wavelength. Instead, it proposes using three typical spectral bands to simulate stellar imaging, and calculate the imaging positions of stars with different spectral types using information from these three spectral bands. By collecting calibration dates using the calibration system, as depicted in Fig. 6, optimization methods are used to calibrate the imaging model parameters of stars with different spectral types. With this calibration result, the imaging model parameters of stars with different spectral types can be compensated after the star has been identified, thereby improving the accuracy of imaging model parameters.Results and Discussions Using the calibration method proposed in the paper, the imaging model parameters corresponding to different spectral types of stars are acquired and presented in Fig.7-9. Building upon these findings, the paper employs the calibration results to compensate for the imaging parameters of identified stars. The experiment demonstrates that the proposed compensation method can effectively reduce the error in measured star angular distance, with detailed comparison results illustrated in Fig.12. Compared to the angular distance measured by existing parameters calibrated using a single spectral band, the root mean square error of star angle distance measured by this compensation method is reduced by 40.81%. Unlike existing methods that rely solely on a single spectral band to simulate stellar imaging, the proposed method offers a more realistic simulation of stars of different spectral types under chromatic aberration. Consequently, it yields more accurate imaging model parameters for stars of varying spectral types, thereby reducing the impact of chromatic aberration on the measurement error of star angular distance.Conclusions This paper begins by acknowledging the differences in the spectral energy distribution among stars of various spectral types, as well as the inherent vertical chromatic aberration in transmission lenses. It proceeds to model and analyze how chromatic aberration affects the imaging model parameters for stars with different spectral types. Furthermore, it introduces a parameter compensation method and validates its effectiveness through field experiments. The findings of this study offer valuable insights and novel research avenues for enhancing the measurement accuracy of star sensors. Future research can explore the use of more spectral bands to simulate stellar imaging, thereby further improving the accuracy of model parameters..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240055 (2024)
[in Chinese]
Arrayed terahertz vector measurement system based on AlGaN/GaN HEMT heterodyne mixer
Kaichu WANG, Qingfeng DING, Qi ZHOU, Xinhang CAI, Jinfeng ZHANG, Kaiqiang ZHU, Zhenjun ZHAI, Houjun SUN, Linjun WANG, and Hua QIN
ObjectiveTo investigate the feasibility and quantify performance metrics of AlGaN/GaN high-electron-mobility transistor (HEMT) heterodyne detectors in the domain of terahertz direction of arrival (DOA) estimation, this study benefits from the high bandwidth and resolution characteristics of terahertz waves, as well as Objective To investigate the feasibility and quantify performance metrics of AlGaN/GaN high-electron-mobility transistor (HEMT) heterodyne detectors in the domain of terahertz direction of arrival (DOA) estimation, this study benefits from the high bandwidth and resolution characteristics of terahertz waves, as well as the process consistency and scalability of AlGaN/GaN high-electron-mobility transistor terahertz heterodyne mixers. A 243 GHz linear array vector detection system based on these mixers was designed and constructed, characterizing its various performance attributes.Methods This paper establishes a 243 GHz linear array vector detection system based on an AlGaN/GaN HEMT mixer linear array (Fig.1(a)). The transmitted terahertz waves to be measured are collimated by an off-axis parabolic mirror (OAP). The receiver uses a high-speed multi-channel ADC array to collect signals from the mixer array, which have been amplified by an intermediate frequency signal amplifier, for processing in the higher-level computer. The processing flow (Fig.2(b)) includes amplitude and phase resolution, calibration, and beamforming.Results and Discussions Testing demonstrates that the system's phase resolution stability is superior to 0.6°, with this error primarily stemming from the phase noise of the microwave source. Future use of a microwave source with lower phase noise and increasing the frequency of the system's intermediate frequency signal for heterodyne detection could further reduce this error. The system exhibits a phase distribution detection relative error of less than 3.6%, attributed to minor discrepancies introduced during the patch assembly of each channel's mixer. Employing more precise assembly techniques in the future could decrease this error. The system's error in detecting terahertz waves arriving from ±11° of the normal direction is less than 0.25°, and the normalized level of the first sidelobe is around -3 dB, due to variations in the response consistency of each channel's mixer. Enhancing the consistency of mixers across channels or increasing the number of elements on the linear array could further reduce sidelobe levels and improve the accuracy of direction of arrival detection. The system's field of view reaches 22°, a result of the current 3 mm spacing between linear array elements leading to insufficient spatial sampling rates for terahertz waves and a limited field of view constrained by the 3 mm superhemispherical silicon lens used to couple the measured terahertz waves. Future efforts will focus on reducing the spacing between linear array elements and adopting a more optimal coupling method for the measured terahertz waves to enhance the overall field of view of the system.Conclusions This paper establishes a 243 GHz terahertz linear array vector detection system characterized by high phase resolution stability and low error in the direction of arrival detection. By comparing test results with simulation outcomes, it was found that the system's phase distribution detection error is less than 3.6%, the error in detecting terahertz wave direction of arrival within ±11° of the normal direction is less than 0.25°, and the field of view reaches 22°. These results validate the feasibility of applying AlGaN/GaN HEMT heterodyne detector linear array components in the field of terahertz DOA estimation. This lays the groundwork for the subsequent development of terahertz phased array radars and directional communication systems with larger fields of view and smaller system sizes..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240088 (2024)
[in Chinese]
Experimental study and infrared detector application research of Micro Miniature Refrigerators
Xin TONG, Ming XIA, Shufen LI, Jiapeng LI, Yang HUAI, and Jie QIU
ObjectiveThe Micro Miniature Refrigerator（MMR） is a novel Joule-Thomson cryocooler manufactured by micro-machining technologies, its axial length is significantly shorter than traditional Joule-Thomson cryocoolers commonly employed in infrared detectors. MMRs can greatly reduce the size of infrared detectors upon succeObjective The Micro Miniature Refrigerator（MMR） is a novel Joule-Thomson cryocooler manufactured by micro-machining technologies, its axial length is significantly shorter than traditional Joule-Thomson cryocoolers commonly employed in infrared detectors. MMRs can greatly reduce the size of infrared detectors upon successful implementation. However, contemporary MMR products encounter challenges such as relatively low cool-down rates, cooling power, and structural strength. To address these issues and enhance the cool-down performance of the MMR for effective application in infrared detectors, a calculation model describing flow and heat transfer besides working characteristics of the MMR is proposed and verified. MMR prototypes are fabricated and experimentally studied. Building upon theoretical analysis and experimental findings optimization methods including transitioning the MMR material from glass to metal and modifying the structure and channel patterns of the MMR are introduced, the cooling performance of the MMR is thus greatly improved. Furthermore, an integrated design incorporating an MMR into an infrared detector is also proposed.Methods A novel calculation model implemented through C language programming is proposed and verified by experiments, based on the calculation model the flow and heat transfer characteristics in micro-channels of MMR is obtained. The theoretical insights derived from the calculation model guide the fabrication of a glass MMR prototype. This prototype becomes the focal point of experimental studies, providing a tangible platform for validating the theoretical model. The liquefaction of the working fluid during experimentation serves as a crucial validation step, affirming the accuracy and applicability of the theoretical framework. Building upon theoretical analysis and experimental findings, optimization methods are introduced to address the identified challenges. Notably, significant improvements are achieved by transitioning the MMR material from glass to metal and incorporating adiabatic slots. These optimization measures result in a remarkable enhancement of the MMR's cooling performanceResults and Discussions The optimization methods, particularly the transition from glass to stainless steel and the incorporation of adiabatic slots, prove to be highly successful. The resulting stainless steel MMR prototype demonstrates a rapid 68-second cool-down time (cool down to 123 K) and a substantial cooling power of 1 102 mW. The research extends beyond the standalone MMR improvements to propose an integrated design incorporating the MMR into an infrared detector. This innovative integration results in a remarkable reduction of the detector's axial length by 65.3% compared to conventional infrared detectors. The integration holds promise for enhancing the miniaturization and integration of infrared detectors. The exploration of materials extends to the development of a Kovar alloy MMR, building upon the successes achieved with the stainless steel counterpart. The Kovar alloy MMR not only facilitates integration into infrared detectors but also exhibits an ability to withstand a high working pressure of 60.9 MPa and achieve a rapid 38-second cool-down time (cool down to 126 K) under 60 ℃ temperature conditions. These advancements showcase the adaptability and versatility of the MMR in varying working conditions.Conclusions The MMR, as an innovative Joule-Thomson cryocooler, holds a distinctive advantage in significantly reducing the axial length of infrared detectors. This characteristic is identified as a key driver in advancing the miniaturization and integration of infrared detectors. The theoretical insights obtained from the calculation model guide the fabrication of a glass MMR prototype, allowing for the liquefaction of the working fluid and validation of the theoretical model through experimental research. The success of optimization strategies, particularly the transition to stainless steel and the introduction of adiabatic slots, stands out as a pivotal achievement. The resulting improvements in cooling performance demonstrate the efficacy of informed optimization measures in overcoming the challenges faced by contemporary MMRs. The integration of the MMR into an infrared detector and the subsequent advancements with the Kovar alloy MMR underscore the practical applications of this research. The proposed integrated design showcases a substantial reduction in axial length. The Kovar alloy MMR and the integrated infrared detector design exhibit several advantages over similar products reported in the literature. These include higher reliability, reduced structural complexity, and ease of fabrication. The cumulative technical advantages position the proposed MMR and infrared detector design as promising contributors to the broader field of cryocooler technology..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20230728 (2024)
Experimental study on ground simulation measurement of infrared radiation characteristics of satellite in orbit
Changliang LI, Dongxing TAO, Hanchen YU, Huahua LIU, Yonghong SHANG, and Zhaokun ZHU
ObjectiveAccurate, multi-spectral and multi-angle infrared radiation characteristics data of satellite targets are of great significance for the identification of satellite types, functions, key instruments (such as solar wings, antennas, etc.) and the monitoring of satellite working status in orbit. At present, due toObjective Accurate, multi-spectral and multi-angle infrared radiation characteristics data of satellite targets are of great significance for the identification of satellite types, functions, key instruments (such as solar wings, antennas, etc.) and the monitoring of satellite working status in orbit. At present, due to the limitation of measurement means and calibration level, the infrared characteristic data obtained by in-orbit measurement generally contains only a few pixels, and there is a lack of high-resolution infrared imaging data of satellites in orbit. Using the opportunity of vacuum thermal test in the satellite development stage, high quality infrared simulation characteristic data measurement of satellite in orbit could be implemented. The traditional method is to place the thermal imager outside the environmental simulation container and to measure the infrared characteristics of the target inside the container through an optical window mounted on the container. Meanwhile, the infrared background of the natural environment and the infrared radiation of the thermal imager will be reflected back to the thermal imager by the optical window. And there will be obvious "ghost shadow" of the natural environmental background and the thermal imager on the optical window. Through the vacuum low-temperature adaptive design, the infrared thermal imager can be placed in the environmental simulation container, and the influence of the optical window can be eliminated from the root, and the accuracy of the infrared radiation characteristics data can be greatly improved.Methods An oil removal process ensures the normal use of the infrared thermal imager under vacuum conditions better than 5×10-4 Pa. The active and passive thermal protection are carried out respectively through a thermal control system placed on the shell surface of the thermal imager and a specific shield designed for the thermal imager. Thus, the temperature control requirement of the thermal imager in the range of -10 ℃ and 20 ℃ is satisfied under the environmental condition of -173 ℃. On the other hand, through the thermal control treatment of the thermal imager shield surface, the emissivity and the heating rate of the thermal imager under high temperature environment are reduced, and the long-term use of the thermal imager under the long-term irradiation environment of the solar simulator is ensured. Through the integrated design of infrared thermal imager and PTZ, the horizontal rotation and up and down pitching motion of thermal imager on PTZ are realized.Results and Discussions The low-temperature blackbody developed by Beijing Institute of Spacecraft Environment Engineering (BISEE) was used as the calibration source of the thermal radiation, and four position points around the target on temperature measurement surface are selected where four thermocouples T1-T4 are pasted on(Fig.5). The temperature measured by the thermocouples was taken as the actual temperature and compared with the temperature data of points P1 to P4 set at the same position in the screen of the thermal imager. The temperature measurement error of the thermal imager is ±3 ℃, and the thermal imaging remains stable with a temperature measurement error close to 0 ℃. At the same time, there is no 'ghost shadow' phenomenon in the infrared image of the calibration source collected by the thermal imager.Conclusion Using the opportunity of vacuum thermal test in the satellite development stage, clear and accurate satellite in-orbit simulation infrared images can be obtained by developing and transforming infrared acquisition equipment adapted to the vacuum low-temperature environment. These images can support the research of satellite in-orbit status monitoring and function analysis based on infrared characteristic data, and can also support the demonstration and construction of infrared sensor related equipment..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240040 (2024)
Monocular dynamic 3D active thermography based on joint laser scanning thermography
Baoyuan DENG, Yunze HE, Hongjin WANG, Qun DENG, and Yaonan WANG
ObjectiveIn order to improve the defect detection capability of large-sized specimens, line scanning thermography has become an effective non-destructive testing method for building, metal, aircraft components and carbon fiber reinforced composite materials. The current line scanning thermography method is difficult toObjective In order to improve the defect detection capability of large-sized specimens, line scanning thermography has become an effective non-destructive testing method for building, metal, aircraft components and carbon fiber reinforced composite materials. The current line scanning thermography method is difficult to provide intuitive detection results for specimens with complex morphologies. Therefore, the three-dimensional thermography integrating detection specimen surface contour geometric data is receiving increasing attention. In order to meet the demand for non-destructive testing of non-planar carbon fiber composite plastic specimens with complex morphology, this paper proposes a system that uses only one thermal imager to perform active three-dimensional thermography on moving specimens, called monocular dynamic 3D active thermography. The system integrates the 3D contour of the specimen with an active thermography inspection, and is capable of inspecting composite specimens with complex geometries and giving intuitive thermography defect inspection results.Methods This proposed monocular dynamic 3D active thermography system consists of a line laser, a thermal camera, an actuator, and a calibration board and does not require an additional 3D profiler (Fig.1). Compared with traditional 3D active thermography detection methods that require additional 3D cameras to obtain surface contour information of the detection object; This system does not require an independent 3D sensor, and the thermal imager acts as both a three-dimensional sensor and a temperature sensor. To achieve this function, based on laser joint line scanning thermography, this paper proposes a mathematical model that unifies the line scanning model and the pinhole camera projection model, and uses the line laser as the thermal excitation for active thermography and the spatial encoding for 3D reconstruction. The algorithm realizes 3D reconstruction, spatio-temporal reconstruction for nondestructive inspection, and the registration of the reconstructed thermogram sequence and the 3D point cloud (Fig.2).Results and Discussions Experimental system of monocular dynamic 3D active thermography used FLIR 6702and a 20 W laser with a center wavelength of 808 nm is established (Fig.3). The standard height specimen calibration experimental results show that, in the height measurement range of 1 mm to 150 mm, the average error is 0.16 mm, and the maximum error does not exceed 0.25 mm (Fig.4). The carbon fiber intake pipe experiment shows that the method has the ability to reconstruct the 3D temperature field of large-size carbon fiber composites and detect the defects (Fig.5). Compared with other 3D thermography techniques, the advantage of the proposed system is its simple structure, which is a single camera, single excitation 3D thermography system without the need for additional 3D measuring instruments or complex feature extraction and matching algorithms. The limitation lies in the fact that only laser can be used as both a thermal excitation for active thermal imaging and a spatial encoding for 3D reconstruction. It can only achieve active thermal imaging with laser excitation and has certain limitations on the wavelength distribution and power of the laser. Therefore, the proposed active 3D thermal imaging technology is specifically designed for the detection of carbon fiber composite.Conclusions The monocular dynamic 3D active thermography system is proposed in this paper for 3D measurement, defect detection and 3D temperature filed measurement. Based on the joint line scanning thermography, this paper achieves three-dimensional measurement function by the jointly calibration of the inspected object, laser, and infrared camera. With only one calibration board added, this paper proves that thermal imaging can achieve three-dimensional measurement and the experiment distance measurement error is controlled within 0.25 mm. The proposed system works fast, robust, and can be used for quality control on the production line..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240047 (2024)
Research on the thermomechanical architecture of Dewar of the large format infrared detector (inner cover paper)
Yang ZHANG, Defeng MO, Jun LI, Xinmin SHI, Cui FAN, and Xue LI
ObjectiveWith the increasing requirements for the resolution, large field of view, and multi spectral range of infrared detectors in fields such as astronomical telescope, military warning, and space remote sensing, staring large-scale array and scanning long line array infrared detectors have been developed. The size Objective With the increasing requirements for the resolution, large field of view, and multi spectral range of infrared detectors in fields such as astronomical telescope, military warning, and space remote sensing, staring large-scale array and scanning long line array infrared detectors have been developed. The size of the infrared focal plane is limited by the size of the readout circuit of the detector chip and the size of the detector material. The large format infrared detector has the problems of high cost, unstable performance and low uniformity. Therefore, infrared detector splicing technology is an important means to solve this problem. The splicing methods of infrared detector are mainly divided into optical splicing and mechanical splicing. The mechanical splicing method receives the optical system image directly on the focal plane because it does not add redundant optical components, and has the advantages of small energy loss and simple system structure. At present, many international projects, including astronomical telescopes, dark energy detection telescopes or ground-based telescopes, have gradually begun to carry the splicing large format infrared detector load as the core detection component, and the detector module as the splicing unit is getting larger and larger, and the total scale of the splicing detector is also getting larger and larger. Subsequently, the technical requirements of temperature control, high precision splicing and mechanical properties of splicing large array infrared detector components have been improved. According to the performance requirements of multi-module splicing of large format infrared focal plane package, the structure of Dewar component was analyzed and designed, and the mechanical and thermal properties of the component were verified. Finally, the large format infrared detector Dewar component met the requirements of the project.Methods The key structure of the multi-module spliced large format infrared detector Dewar was designed. A three-point adjustable module structure based on precision shim was adopted (Fig.3), and a multi-point coupled flexible cold strap structure with high thermal conductivity, as well as SiC cold platform structure with low stress and high uniform temperature, were designed (Fig.4). In addition, key technologies such as precision splicing of detector module, temperature uniformity of large format focal plane, low heat loss of large Dewar component, and mechanical reliability of cold platform component were studied. Liquid nitrogen refrigeration was used to test the low temperature field of large format infrared detector Dewar (Fig.8), and the flatness of the focal plane array was measured by three-dimensional imaging instrument. Finally, the mechanical vibration test of the component was carried out (Fig.10).Results and Discussions The 2 k×2 k infrared detector module was spliced with a 3×3 array, and the total size of the focal plane array reached 6 k×6 k. The temperature uniformity of the 9 module array was ± 0.45 K, and the 9 module array was ± 0.45 K, and the flatness of the focal plane array after module splicing was better than ± 10 µm. The heat loss of the large Dewar component at room temperature was 7.53 W. The mechanical vibration test of Dewar component shows that the minimum fundamental frequency of XYZ three directions is 557 Hz, and after 9 grms random vibration, the function of the component is normal, without obvious changes, and can meet the requirements of engineering applications.Conclusions Design the package structure for the spliced large format infrared detector Dewar, by using the zirconia support structure with high stiffness and low thermal conductivity, the SiC cold platform with high thermal conductivity and low thermal expansion coefficient, as well as the interface material with high elasticity and high thermal conductivity, and analyze and design the key structure of Dewar component such as the detector module installation structure based on three-point adjustment, the cold platform structure and the multi-point coupling cold strap structure. Implemented a 6 k×6 k large format infrared detector Dewar module based on a 2 k×2 k 18 µm center to center distance detector module assembled in a 3×3 array. Mechanical vibration and thermal tests are carried out to verify that the components meet the index requirements of the large format infrared detector Dewar component. After the detector module is spliced, the flatness of the focal plane array is better than ± 10 µm, the focal plane temperature uniformity is better than ± 1 K, the heat loss of the Dewar component is better than 7.53 W, and the Dewar component passes the 9 grms random vibration test. The fundamental frequency of the Dewar component reaches up to 557 Hz. The key performance index is basically equivalent to the main international spliced large format infrared detector component, which meets the engineering application requirements..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240083 (2024)
Calculation of the angle factor of the cryogenic infrared detector Dewar
Changhang ZENG, Jun CHEN, Yibin HUANG, Mingwei WANG, Hai REN, and Youyu GAN
ObjectiveThe angle factor is a crucial parameter in the calculation of radiation heat transfer between surfaces. The commonly used methods for calculating radiation heat transfer in diffuse gray surface system, such as the net heat method and network method, utilize energy flux density (emissive power) and angle factorObjective The angle factor is a crucial parameter in the calculation of radiation heat transfer between surfaces. The commonly used methods for calculating radiation heat transfer in diffuse gray surface system, such as the net heat method and network method, utilize energy flux density (emissive power) and angle factor to describe the energy relationship during the process of radiation heat transfer. Whether it is the net heat method or network method, it is necessary to calculate the angle factor between any two surfaces. With the development of large focal plane array, long-linear-array, dual/multi-band, digital infrared detector technology, the size and structure complexity of dewar gradually increased. The traditional methods calculating the radiation heat generally simplified dewar to the coaxial cylinder model, resulting in significant calculation errors. Therefore, the accurate calculation of dewar radiation heat transfer is essential. The inside of the dewar is a high vacuum, and its radiative heat transfer belongs to the category of radiative heat transfer between surfaces. To calculate the radiation heat transfer, the angle factor should be calculated first. This paper mainly studied the calculation of the angle factor of dewars.Methods The Monte Carlo method was used to calculate the angle factors of the dewar. 3ds Max was used to extract the surfaces involved in radiation for modeling and triangulating to enhance the universality of the calculation (Fig.1, Fig.17). A calculation program was developed. The calculation process mainly included randomly arranging the well-distributed emission points (Fig.4), generating the emission direction constrained by Lambert's law (Fig.7), and tracing energy bundle based on the whole dewar model.Results and Discussions The angle factors and relative errors of three typical models were calculated to verify the correctness of the program. The calculation result showed that the relative error could be controlled between 1% and -1% with the increase of the number of energy bundles(Fig.12, Fig.13, Fig.14, Fig.15). The angle factors of a certain type of dewar were calculated and 12 of them were provided (Tab.4). Monte Carlo method is an efficient calculation method for compact dewars and statistically significant results could be obtained when the number of energy bundles reaches the level of ten thousand.Conclusions A general calculation program for calculating the angle factors between the radiation surfaces of dewar was obtained. The angle factors of one surface to multiple surfaces could be calculated at one time. The angle factors of a certain type of dewar were calculated. The angle factor of the window to the optical filter was 0.5617, the angle factor of the window base to the cold shield was 0.4875, the angle factor of the main cylinder to cold finger was 0.3069, and the angle factor of the getters to the cold finger was 0.1879. After obtaining the accurate angle factors, the radiant heat transfer of dewar can be calculated accurately by combining the calculation methods of radiant heat transfer between surfaces, such as the net heat method and the network method..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240106 (2024)
[in Chinese]
All-optical laser ultrasonic detection of defects among BGA solders
Yang LIU, Peng SONG, Xiangyue LIU, Jianghao ZHAO, Cong LIU, and Junyan LIU
ObjectiveBall Grid Array (BGA) is a widely used modern integrated circuit packaging method, which plays an important role in aerospace, vehicle manufacturing, electronic communications and other fields due to its large number of I/O pins, small size, and good heat dissipation performance. Because of technical and envirObjective Ball Grid Array (BGA) is a widely used modern integrated circuit packaging method, which plays an important role in aerospace, vehicle manufacturing, electronic communications and other fields due to its large number of I/O pins, small size, and good heat dissipation performance. Because of technical and environmental influences, BGA solder joints are prone to have various defects. In order to ensure the reliability of electronic packaging, it is necessary to inspect them with a high-precision, high-reliability non-destructive testing technology. Laser ultrasonic detection technology has the advantages of high precision, fast response, no damage, etc. Optical microphone is a new type of ultrasonic receiving device, which has low cost, wide bandwidth range, high sensitivity and a broad development stage. Therefore, a ultrasonic detection of BGA solders based on optical microphone is studied in this paper.Methods In this paper, the process of ultrasonic wave excitation by pulsed laser on the surface of the material is theoretically analyzed, and the thermal-mechanical coupling numerical simulation model of BGA solder joint is established by using the finite element simulation software COMSOL to simulate the propagation law of ultrasonic waves inside the solder joint and the influence of internal defects on ultrasonic propagation. Finally, the laser ultrasonic testing system based on optical microphone was used to perform laser ultrasonic scanning tests on the prepared BGA package circuit board samples with simulated defects, and the results were processed by Lanczos denoising algorithm.Results and Discussions The results show that the laser with a wavelength of 532 nm and a single pulse energy of 2.66 mJ can detect solder joints with defects with diameters of 7 mm and 5.5 mm. The position and size of the solder joints and simulated defects in the C-scan results are consistent with the actual situation (Fig.9). The A-scan results (Fig.10) are consistent with the simulation results (Fig.6). In the B-scan results (Fig.11), there is a significant difference between the normal solder joint area and the simulated defect area.Conclusions Through the theoretical analysis, finite element simulation and experimental detection of the process of laser exciting ultrasonic on BGA samples, it is proved that the all-optical laser ultrasonic detection can effectively detect the solder joint defects in BGA packaging. Laser ultrasonic testing has unique advantages in locating and dimensioning BGA solder joint defects, and has broad development prospects in the field of real-time quality inspection in the process of integrated circuit manufacturing and usage..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240072 (2024)
1.74 μm mode-locked semiconductor laser with a high-strained InGaAs/InGaAsP multi-quantum wells structure
Yang DUAN, Zhongxi LIN, and Hui SU
ObjectiveThe InP-based mode-locked semiconductor lasers have attracted considerable interest for their ability to generate pulses with high repetition frequency. However, they can hardly reach 1.7 μm wavelength range due to the difficulty on growing indium-rich highly strained quantum wells, which limits their applicatObjective The InP-based mode-locked semiconductor lasers have attracted considerable interest for their ability to generate pulses with high repetition frequency. However, they can hardly reach 1.7 μm wavelength range due to the difficulty on growing indium-rich highly strained quantum wells, which limits their application on optical frequency combs, medical photoacoustic imaging and gas detection. For the purpose of chip-scale sensing in the mid-infrared region, this paper designs a 1.7 μm InP-based monolithic mode-locked semiconductor laser.Methods The laser structure was grown an (100) oriented n-InP substrate by Metal-organic Chemical Vapor Deposition (MOCVD). The undoped active zone of the laser contains three compressively strained 8-nm-thick InxGa1-xAs quantum wells separated by 12-nm-thick InxGa1-xAsyP1-y, which is enclosed between 300-nm-thick InGaAsP layers (Fig.1(a)). The MOCVD-grown wafer is processed into ~1.9-μm-wide ridge waveguide using standard optical processing (Fig.1(b)). The 4178-μm-long colliding-pulse mode-locked laser (MLL) is achieved with an ~168-μm-long saturable absorber located at the center of the cavity (Fig.1 (c)).Results and Discussions The threshold current of the device is 83 mA without bias voltage, and the maximum output power is 25.83 mW (Fig.3(b)). According to the relation between external quantum differential efficiency and cavity length (Fig.3(a)), the internal loss of this epitaxial structure is calculated to be 14.378 cm-1. An efficient mode locking has been achieved at 1.74 μm with a repetition frequency of 19.3 GHz, the narrowest linewidth of RF spectra is 14 kHz (Fig.4(a)), and the period of pulse train is 51.88 ps (Fig.4(b)). A microwave signal appears at a gain current of 130 mA when VSA=-1.6 V, and its RF spectrum drops down to tens kHz with increasing current (Fig.5). Decreasing the reverse bias voltage from -1.4 V to -2 V with forward current at 520 mA, the laser emission spectrum gradually broadens (Fig.6). The 9.88-nm-wide spectrum contains more than 40 longitudinal modes spaced by 0.2 nm when VSA=-2 V.Conclusions This paper presents a monolithic colliding-pulse mode-locked semiconductor laser based on high-strained InxGa1-xAs/InxGa1-xAsyP1-y multi-quantum wells structure. The laser exhibits stable mode-locking operation with a repetition frequency of 19.3 GHz at 1.74 μm. By comparing the current and the reverse bias voltage influences on RF spectrum and emission spectrum, it proves that the monolithic InP-based device can provide a stable and efficient mode-locking above 1.6 μm range..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240079 (2024)
Theoretical study of “zigzag” resonance condition in angled cavity laser diode
Shunchao YU, Ziao GONG, Yonggang ZOU, Yingtian XU, and Jie FAN
ObjectiveLaser diodes have great demands in material processing and space communication because of their small size and high electro-optical conversion efficiency. However, due to the nonlinear effect, the traditional broad-area lasers are prone to filamentary emission and face the problems of large divergence angle anObjective Laser diodes have great demands in material processing and space communication because of their small size and high electro-optical conversion efficiency. However, due to the nonlinear effect, the traditional broad-area lasers are prone to filamentary emission and face the problems of large divergence angle and poor lateral beam quality, which limit their direct application. Angled cavity laser diodes have a unique oscillation optical path in which the fundamental lateral mode satisfies zigzag resonance, then the high-order lateral modes and filamentation effects in the broad-area lasers can be suppressed effectively. Presently, most of the angled cavity laser diodes are designed with a strong index guiding to total internal reflection of the fundamental lateral mode on the sidewalls, the non-radiative recombination loss is enhanced because the etching depth exceeds the active region. However, the resonance condition of the fundamental lateral mode is deviated as the etching depth decreases. Therefore, it is necessary to research angled cavity laser diodes with weak index guiding structure. For this purpose, the zigzag resonance conditions of angled cavity laser diodes in different etching depths are studied.Methods Based on the stationary phase method, this paper gives a theoretical model containing the GH shift factor for strong and weak index guiding. The influence of the GH shift in the angled cavity laser diodes on the zigzag resonance condition of the fundamental mode is discussed theoretically (Fig.2), and the new fundamental lateral mode zigzag resonance conditions containing the GH factor are clarified. It is pointed out that the corresponding shallowest critical etching depth Dc,m exists for each order lateral mode, and the mode selection characteristics of the angled cavity under the fundamental lateral mode critical etching depth Dc,0 are analyzed.Results and Discussions The GH shift factor in the angled cavity is studied based on the stationary phase method, and a theoretical model for strong and weak index guiding is given. Comparative analysis shows that the calculation results of the theoretical model are in good agreement with the simulation results under the two types of index guiding and can more accurately describe the resonance of the fundamental lateral mode in the angled cavity under the weak index guiding (Fig.3-Fig.4). The analysis of the theoretical model shows that there exists a corresponding critical etching depth Dc,mfor the m-order lateral mode, when the etching depth of the angled cavity is less than Dc,m, the limiting effect of the waveguide on the m-order lateral mode decreases drastically, so the angled cavity exhibits a strong mode selective ability near the fundamental lateral mode critical etching depth Dc,0 (Fig.5).Conclusions The theoretical model of the angled cavity for strong and weak index guiding is obtained through the theoretical analysis of the GH shift inside the angled cavity, and the critical etching depths Dc,m of lateral modes are given according to the effective refractive index method and the Snell's law. Combined with the software simulation, it shows that the GH shift is proportional to the ridge width W and inversely proportional to the waveguide tilt angle θ, which has a great influence on the zigzag resonance conditions of the fundamental mode under the weak refractive index. After the GH shift factor is introduced, the theoretical calculation results and simulation results are in good agreement in both strong and weak index guiding, which solves the problem of the zigzag resonance conditions deviation of the fundamental lateral mode under weak index guiding, and helps to improve the coupling efficiency of the fundamental lateral mode. In addition, the etching depth of the angled cavity laser diodes must be larger than or equal to the fundamental lateral mode critical etching depth Dc,0, selected the fundamental lateral mode critical etching depth Dc,0 reduces the non-radiative composite loss of the sidewalls and enhances the selectivity of high-order lateral modes at the same time compared with the strong index guiding..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240113 (2024)
Design of optical axis monitoring system for space-borne lidar
Yuan WAN, Rui LI, Yang ZHANG, Jinru YUAN, Heng XIONG, Guowei ZHOU, Jiqiao LIU, and Xia HOU
ObjectiveWith the increasing seriousness of global atmospheric environmental pollution, spaceborne lidar, as a new type of active remote sensing instrument, has become an important load for global atmospheric measurement, which can achieve high-precision measurement of atmospheric components such as greenhouse gases, pObjective With the increasing seriousness of global atmospheric environmental pollution, spaceborne lidar, as a new type of active remote sensing instrument, has become an important load for global atmospheric measurement, which can achieve high-precision measurement of atmospheric components such as greenhouse gases, particulate matter, and aerosols. Compared with the passive detection of spaceborne cameras, lidar has more stringent requirements for the stability of optical systems. The mechanical impact during the orbiting process, the change of gravity field during the orbiting operation, the change of temperature, the release of internal stress, and the jitter of the satellite platform will cause the structural deformation of the main optical machine of the lidar, thereby destroying the consistency of the optical axis of the radar transceiver and causing a decrease in detection efficiency. In addition, the change of the direction of the lidar optical axis relative to the star sensor will lead to the deviation of the radar optical axis relative to the reference measurement attitude. Therefore, high-precision transceiver optical axis monitoring and matching technology is necessary for active detection of remote sensing functions. The optical axis monitoring unit is used to monitor the real-time variation of the transceiver optical axis, which is an important part of the optical axis matching feedback mechanism.Methods Figure 1 shows the main components of the visual axis monitoring system, including the active 785 nm reference light source, the visual axis camera, the CCD focusing lens group, the eyepiece, the receiving optical axis prism, the star sensor reference mirror, the beam combiner and the beam splitter. The active reference light source in the system uses a laser diode with a wavelength of 785 nm. After the tail fiber output laser is collimated and shaped, it first passes through the beam splitter M1. In this process, about one-tenth of the beam energy is reflected into the surveillance camera as a reference optical axis. Subsequently, the reference light is beam-divided again by 1 : 1 through the M2 mirror. This part of the light is reflected by the reference prism of the star sensor and imaged on the surveillance camera to capture the information of the star-sensitive optical axis. The light beam separated by the M2 mirror is reflected by a hollow mirror and enters the telescope system, and is reflected back to the surveillance camera through a light-taking prism located next to the secondary mirror, so that the direction change information of the received optical axis can be obtained. In addition, the emitted laser is split by a beam splitter before output, and a small amount of emitted laser enters the surveillance camera by turning and combining the beams to obtain the change information of the laser emission optical axis. The simulation results show that the imaging quality of the four optical axis monitoring channels reaches the diffraction limit level, and the design accuracy of the receiving and transmitting optical axis monitoring can reach 0.09 μrad and 2.28 μrad respectively.Results and Discussions The experimental verification of spaceborne lidar in vacuum and space thermal environment was carried out. A test system in vacuum environment was built to calibrate the optical axis pointing of lidar. The optical axis change data measured by the optical axis monitoring unit and the tank test system were compared. The test results are shown in Fig.12. The pointing fluctuation of the transmitting optical axis measured by the optical axis monitoring unit is ± 1.14 μrad ( corresponding to a pixel jump ). At this time, the pointing jitter of the transmitting laser measured by the monitoring system in the tank is better than ± 1.5 μrad ; the pointing fluctuation of the receiving optical axis measured by the optical axis monitoring unit is ± 1.2 μrad, and the corresponding jitter measured by the tank monitoring system is ± 3.5 μrad. By comparison, it is found that both of them have the same periodic fluctuation, and the fluctuation cycle is consistent with the track thermal environment cycle. The optical axis monitoring accuracy of the transmitting optical axis is limited by the angular resolution of the channel of 2.28 μrad. There is a deviation of about 3 μrad between the visual axis system for monitoring the receiving optical axis and the in-tank test system. The reason is that the beam has a long transmission path in the in-tank test system, which is easily affected by vibration and temperature deformation during the operation of the vacuum equipment. The optical axis data after the stable operation of the lidar is analyzed. The optical axis change data is shown in Fig.13. The data analysis shows that the stability of the optical axis of the lidar is better than 3 μrad after the stable operation of the lidar in orbit.Conclusions In this paper, a space-based multi-optical axis monitoring method is proposed for the on-orbit stability requirements of Atmospheric Environment Monitoring Satellite (DQ-1) Aerosol and Carbon dioxide Detection Lidar (ACDL), and a set of lidar optical axis monitoring optical machine system is designed. By using the integrated imaging scheme of active laser light source, the on-orbit synchronous high-precision monitoring of lidar transceiver optical axis under space-based coordinate reference is successfully realized. The high precision and high reliability of the monitoring technology in the space environment are verified by the vacuum thermo-optical calibration test in the ground space environment. After the lidar is launched into orbit, the optical axis monitoring unit works normally in orbit. The optical axis monitoring unit used in this paper has high environmental reliability and stability, and can be applied to other optical axis monitoring modules of active and passive space optical loads, which has important reference value and guiding significance..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240118 (2024)
Design and implementation of high precision on-line measurement system for pulse parameters of ArF Excimer laser
Wanqi ZHAO, Rui JIANG, Zebin FENG, Ze XU, Ning GUO, Yan JIANG, and Jingguo ZHU
ObjectiveThe laser with stable output energy is critical for lithography. For the closed-loop control of the deep-ultraviolet excimer light source, the laser pulse parameters need to be measured on-line with high precision. Traditional excimer laser energy measurement devices are based on low repetition rate. In order Objective The laser with stable output energy is critical for lithography. For the closed-loop control of the deep-ultraviolet excimer light source, the laser pulse parameters need to be measured on-line with high precision. Traditional excimer laser energy measurement devices are based on low repetition rate. In order to meet the pulse measurement requirements of high repetition rate excimer lasers, the on-line measurement system for pulse parameters of high repetition rate excimer laser is designed. The pulse energy acquisition is realized by using peak holding circuit and high speed ADC. The optimization method for peak holding circuit design is proposed by simulating the parasitic equivalent model of peak holding circuit.Methods The measurement system for pulse parameters that is designed includes the light path of the former stage and the processing circuit of the latter stage. The measurement system for pulse parameters is placed at the output of the main optical path, and the laser output light passes through the beam splitter, with 95% of the energy output light being used for subsequent lithography work, and 5% of the output light being used for detection, which effectively reduces the loss of the output signal, as shown in Fig.4. The block diagram of the detection circuit is shown in Fig.5. The principle and transient analysis of the peak holding circuit are shown in Fig.6-8. The detection circuit includes a trans-impedance amplification circuit, a filter circuit, a peak holding circuit, and a switching circuit for synchronous triggering of the signal. The peak voltage is maintained and broadened by the peak holding circuit, then the peak value is sampled by a 16-bit 20 MHz high-speed and high-precision ADC, and the collected signal is processed by FPGA.Results and Discussions The test performance of the measurement system for pulse parameters is carried out with an ArF excimer laser. The output of the measurement system for pulse parameters is square wave signal with wide pulse width, which is convenient for ADC acquisition. The response time of the measurement system for pulse parameters is about 150 ns. Besides, the repeatability experiment of the measurement system for pulse parameters yielded a relative error of 0.22% relative to the standard energy meter while the ArF excimer laser works at 6 kHz. And the max relative error is 0.56%. A comparison of the reference energy values of a standard energy meter and those measured by the measurement system for pulse parameters is shown in Fig.13 with the laser operated in constant energy mode. The relationship between the output voltage of the measurement system for pulse parameters and the energy of input signal is shown in Fig.14 with 500 pluses, and the curve is fitted by the least squares method to obtain the fitting relationship. According to the analysis, the correlation coefficient of the linearity is 99.83%.Conclusions The system is designed for measuring the pulse parameters of a deep ultraviolet excimer light source for photolithography, and on-line accurate measurement of the pulse parameters of an excimer laser is achieved. The feasibility of the measurement scheme is verified by comparing the theoretical calculation with the measured results. Based on the equivalent model and response analysis of the hardware circuit, the reason and elimination method of the peak effect of the peak holding circuit are studied. The measurement system was tested on a 193 nm ArF excimer light source at a constant energy mode of 6 kHz, and realized the on-line extraction of repetition frequency and pulse width and the measurement of repetition, consistency and linearity of pulse energy, the results verify that the linearity of the pulse parameter measurement system is 99.83%, the relative error with the standard energy meter is not more than 0.56%, and the average error is 0.22%. It can meet the requirement of on-line measurement of pulse parameters of ArF excimer light source..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240124 (2024)
[in Chinese]
Adaptive sliding mode control by memristor-based neural network and its application
Di LIN, Yiming WU, Sen YANG, Yin ZHANG, and Mingshu ZHAO
ObjectiveIn the optoelectronic pod system, there are various disturbances and unmodeled dynamics. Therefore, it is difficult for conventional control algorithms to adapt to complex situations. The neural network is adopted to realize the adaptive estimation of the unknown dynamics of the model, combined with sliding moObjective In the optoelectronic pod system, there are various disturbances and unmodeled dynamics. Therefore, it is difficult for conventional control algorithms to adapt to complex situations. The neural network is adopted to realize the adaptive estimation of the unknown dynamics of the model, combined with sliding mode variable structure control, the control accuracy can be effectively improved. However, if the neural network estimation fails to converge to the parameters in the actual model at the initial control stage, chattering phenomenon will arise in the sliding mode control. In order to achieve fast convergence of neural network estimation, suppress the chattering at the initial stage of sliding mode control, and improve control accuracy and stability, the algorithm of adaptive sliding mode control based on memristor-based neural network is proposed herein.Methods An improved memristor-based neural network is adopted to store the weight parameters to approach the unmodeled dynamics, which can reduce network convergence time and improve control accuracy compared to the conventional neural network. In the initial stage of sliding mode variable structure control, a neural network based on memristors is adopted. The adaptive gain is improved to reduce the chattering caused by estimation error of neural network. The improved algorithm in overall significantly reduced the chattering and quickly and accurately estimated unmodeled dynamics, enhancing control accuracy and stability. Under analog simulation conditions, the improved algorithm is compared with conventional sliding mode variable structure method regarding to the sinusoidal position response, and the result shows that the convergence time by the improved algorithm is reduced to half of that of the conventional sliding mode control algorithm (Fig.9). When an actual unmanned aerial vehicle tracking detection is conducted in the outfield, the control accuracy under the improved algorithm is increased by 59.18% compared to the conventional sliding mode control algorithm (Fig.12).Results and Discussions Under analog simulation conditions, compared with conventional sliding mode variable structure method, the convergence accuracy for the sinusoidal position response by adopting the improved algorithm is within 0.0002° while the one by conventional algorithm is within 0.001°, which means the convergence time by the improved algorithm is reduced to half of that of the conventional sliding mode control algorithm (Fig.9). When an unmanned aerial vehicle targets detection is conducted in the outfield, with a maximum speed of maneuvering flight of 15 m/s and a distance of 1 km from the unmanned aerial vehicle to tracking turntable, the stably tracking miss distance (RMS) by the conventional sliding mode control algorithm is 0.009 8°, while the RMS by the improved algorithm is 0.004°, approximately 69.8 μrad, resulting in the increase of accuracy under the improved algorithm by 59.18% compared to the conventional sliding mode control algorithm (Fig.12).Conclusions By adopting the improved algorithm of adaptive sliding mode variable structure control based on the memristor-based neural network, the convergence time of estimation for unknown unmodeled dynamics is reduced, up to half of that of conventional sliding mode control algorithm. In an actual outfield detection experiment, the stably tracking control accuracy by the improved algorithm is increased by 59.18% compared to that by the conventional sliding mode control algorithm. The experimental results show that the use of the improved algorithm of adaptive sliding mode variable structure control based on the memristor-based neural network can not only help the system to realize fast convergence and suppress chattering, but also effectively improve the tracking accuracy and stability of the optoelectronic pod system, which has certain application value in engineering..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20230667 (2024)
3D surface reconstruction method through neural-pull based on edge enhancement
Baochang XU, Yihao WANG, Weiwei HAO, Shixuan YIN, Wei WANG, and Yafei LI
ObjectiveSurface reconstruction refers to the process of reconstructing a continuous 3D surface from discrete spatial point clouds data. Learning signed distance functions (SDFs) of an object through spatial discrete point clouds to reconstruct the implicit surface of an object is currently the main research strategy. Objective Surface reconstruction refers to the process of reconstructing a continuous 3D surface from discrete spatial point clouds data. Learning signed distance functions (SDFs) of an object through spatial discrete point clouds to reconstruct the implicit surface of an object is currently the main research strategy. Neural-pull (NP) is a method to obtain high-quality SDFs from discrete point clouds information to reconstruct original surface. The key lies in using the predicted SDFs and the gradient information of the query point to pull the query point onto the reconstructed surface (Fig.1). The advantage of this method is that the model training process does not require ground truth (GT) SDFs as supervision, and at the same time, the signed distance value and gradient information are updated simultaneously during the training process. However, due to the inevitable noise and defects in the actually obtained point cloud data, NP will cause edge defects on the reconstructed surface during reconstruction. Therefore, in order to improve the reconstruction effect of the algorithm, solve the edge defects problem occurs in NP's sparse point clouds reconstruction, this paper proposes an improvement strategy, called neural-pull based on edge enhancement (NPEE).Methods In order to solve the NP edge overfitting problem, this paper proposes the NPEE framework (Fig.2). It consists of edge-construction network (EN) and NP network. EN (Fig.3) uses a residual learning mechanism to learn the edge SDFs of point clouds, ensuring sufficient edge accuracy while ensuring training efficiency. At the same time, based on the original point cloud, the edge factor $ \sigma $ Results and Discussions Using the ABC data set, Stanford scanning model and deep geometric prior data as the ground truth, ideal point clouds reconstruction experiments (Fig.7), sparse point clouds reconstruction experiments (Fig.8) and noisy points cloud reconstruction experiments (Fig.12) are designed to evaluate the algorithm capabilities. The reconstruction results of DeepSDF, Onsurface and NP are compared, and the chamfer distance (CD) of the three groups of experiments are calculated respectively. The experimental results are as follows (Tab.1-6). The reconstruction results of NPEE can show the complete reconstruction model and sufficient edge details.Conclusions In order to improve the reconstruction effect of the algorithm, the edge defects problem occuring in NP's sparse point clouds reconstruction is solved, an improvement strategy is designed, called NPEE. To ensure the reconstructed surface is smooth while obtaining more surface details, on the basis of retaining the original neural network, a new network which uses the residual learning mechanism is designed for learning SDFs of the point cloud while ensuring training efficiency and getting sufficient edge accuracy. At the same time, on the basis of the original point cloud, the edge factor $ \sigma $
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240120 (2024)
[in Chinese]
Research on noise suppression in integrated communication and sensing with photonic reservoir computing (cover paper·invited)
Li PEI, Xiaoyan ZUO, Bing BAI, Jianshuai WANG, Tigang NING, Jing LI, and Jingjing ZHENG
ObjectiveCurrently, two primary types of integrated communication and sensing systems exist, which are forward optical sensing and backward reflected optical sensing. The former faces limitations in sensing signal accuracy, the latter encounters nonlinear effects like four-wave mixing when communication and sensing sigObjective Currently, two primary types of integrated communication and sensing systems exist, which are forward optical sensing and backward reflected optical sensing. The former faces limitations in sensing signal accuracy, the latter encounters nonlinear effects like four-wave mixing when communication and sensing signals occupy separate bands in dense wavelength division multiplexing systems. When both communication and sensing signals share the same frequency band, crosstalk becomes a significant issue. To maintain communication quality, higher input power is often utilized, leading to increased power consumption and nonlinear noise generation. To address these challenges, a noise equalizer is proposed, based on optical reservoir computing (PhRC) chips. The majority of computations are efficiently executed using silicon-based integrated optical devices, offering the dual advantages of reduced latency and expanded bandwidth. This innovative approach holds promise in enhancing the performance and reliability of integrated communication and sensing systems in modern optical fiber networks.Methods This article employs numerical simulation techniques to establish an integrated Rayleigh sensing and 56 Gb/s pulse amplitude modulation (PAM4) communication system (Fig.1). Both the communication and sensing signals utilize a common wavelength of 1 550 nm. The sensing signal uses linear frequency modulation (LFM) modulation pulse with a pulse duration of 248 μs. Initially, the sensing pulse is modulated using a modulator. Subsequently, an optical bandpass filter converts the signal into a single-sideband signal. Then, the PAM4 communication signal is modulated using the modulator and transmitted through an optical fiber. At the optical circulator, sensing signals are detected, while the receiver captures communication signals contaminated by crosstalk and noise. The simulation of the PhRC chip, weight training, as well as the computation of bit error rate (BER) and symbol error rate (SER), were executed using Python (Fig.2). Distorted communication signals are fed into the PhRC to achieve noise equalization.Results and Discussions The weight of the PhRC optical chip noise equalizer is trainable, enabling adaptive equalization for multiple parameters. Under a 20 km fiber condition, the scheme explores the BER equalization capability at incident powers ranging from 5 to 19 dBm. There is a three-order-of-magnitude difference in the BER and SER between the signals before and after equalization with 7 dBm incident power. At an incident power of 10 dBm, the equalization performance is discussed for fiber transmission distances of 15-24 km, a four-order-of-magnitude improvement in BER and SER with 19 km fiber. When using a 20 km fiber and 10 dBm incident power, the scheme is also evaluated for its ability to improve the BER of communication signals affected by 0.5-2.0 GHz LMF sensing pulses. There is a three-order-of-magnitude difference in the BER between the signals before and after equalization at 1.9 G bandwidth of LMF signal. Simulation results indicate that this scheme maintains stable equalization capabilities even when channel conditions change, especially when the input power decreases.Conclusions This article proposes a signal processing scheme for a PhRC chip-based communication and sensing system, utilizing optical computing to achieve noise equalization for a fiber Raman sensing and 56 Gb/s PAM4 communication integrated system. The PhRC chip is capable of equalizing impairments caused by different incident fiber powers, fiber lengths, and LMF bandwidths. It offers advantages such as high integration, large computational bandwidth, low processing delay, and low computational power consumption. Compared to unequalized signals, the equalized signals achieved a three-order-of-magnitude improvement in BER at a lower incident fiber power of 7 dBm, eliminating the need for optimal higher incident power 16 dBm. The scheme supports fiber transmission lengths of 15-24 km and 0.5-2.0 G LFM sensing pulses, achieving over a two-order-of-magnitude improvement in SER and BER. This communication noise processing scheme can achieve low-power and high-quality signal noise recovery, providing a solution for the future development of integrated optical communication and sensing systems..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240191 (2024)
Optical Communication and Sensing
Sensing characteristics of low-loss metallized fiber Bragg grating by ultrasonic welding
Jing TIAN, Lianqing ZHU, Jifeng YAO, Yanming SONG, and Yumin ZHANG
ObjectiveFiber Bragg grating (FBG) is widely used in the structural health monitoring of military industry, water conservancy, aerospace and other fields. FBG needs to be fixed on the object to be measured in a certain way to form heat or strain transfer. Thus, temperature or strain could be measured. Polymer adhesive Objective Fiber Bragg grating (FBG) is widely used in the structural health monitoring of military industry, water conservancy, aerospace and other fields. FBG needs to be fixed on the object to be measured in a certain way to form heat or strain transfer. Thus, temperature or strain could be measured. Polymer adhesive is widely used in traditional FBG sensor packaging. The drawback is that polymer is prone to creep and aging during long-term use. Therefore, the deformation transfer between FBG and the measured object is mismatched, which makes the sensor ineffective. To solve this problem, metal alloy is adopted as a stable packaging material for metalizing fiber Bragg grating. Because the existing metallization method has great influence on the transmission loss caused by FBG, ultrasonic welding is studied for metallization. The temperature and strain sensing performance of the metallized sensor is verified.Methods The fiber grating was metallized by ultrasonic welding. The selected FBG is encapsulated on the beam of equal strength with tin alloy in the form of full package. The transmission and reflection spectra of FBG before and after package were observed. Temperature sensing experiments (-75-150 ℃) and strain sensing experiments (-560-560 με) were carried out to verify the temperature and strain sensing characteristics of the metallized fiber grating sensor.Results and Discussions The shape of FBG reflection spectrum of full-wrap package is a little distorted when the package is just finished. But the degree of distortion does not affect the calculation of the central wavelength of reflection spectrum. The package transmission loss is approximately 0.04 dB(Fig.4). The full package fiber grating can realize the sensing of the entire experimental temperature experimental test range. Its temperature sensitivity is about 2.95 times that of unpackaged FBG (Fig.5). During the long, high temperature process of the temperature sensing experiment, stress release ameliorates the distortion of the reflection spectral shape of the FBG when the package is just completed (Fig.6). The shape of the reflection spectrum of the fully packaged fiber grating is affected by the strain load, but the degree of deformation does not affect the sensing effect (Fig.7). The strain sensing of the sensor has high measurement accuracy (Tab.2).Conclusions The ultrasonic welding method was used to metalize FBG with full-wrap surface-mount type. The transmission loss of the metal-packaged FBG sensors were less than 0.04 dB. Compared with other metallization methods, the transmission loss is reduced by one order of magnitude. Low-loss package effect of FBG surface mount metallization package is achieved. Temperature sensing experiments and strain sensing experiments were carried out on the packaged FBG sensor. The experimental results showed that the temperature sensitivity coefficient and strain sensitivity coefficient of the full-wrap package FBG sensor are 26.44 pm/℃ and 1.18 pm/με, respectively. The correlation coefficient R-Squared of temperature and strain sensing are both above 0.999 6. The reliability of temperature sensing and strain sensing of the sensor is verified. It can be seen that the ultrasonic welding method could be effectively used to metallize FBG. It can not only play a role of protecting FBG and improving sensitivity, but also realize the production of FBG temperature and strain sensors in a simple, low loss and reliable way..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240080 (2024)
Satellite antenna deformation reconstruction technology based on FBG sensors
Jichun ZHAO, Yuanhao LI, Yumiao SONG, Guowen AN, Pinggang JIA, and Jijun XIONG
ObjectiveIn the current era of rapid digitalization, communication satellites play an extremely crucial role. When satellites are in orbit, the antenna is subject to temperature and external mechanical forces, resulting in thermal and mechanical deformations. These deformations cause distortions in the beam direction, Objective In the current era of rapid digitalization, communication satellites play an extremely crucial role. When satellites are in orbit, the antenna is subject to temperature and external mechanical forces, resulting in thermal and mechanical deformations. These deformations cause distortions in the beam direction, significantly impacting the quality and reliability of information transmission. Therefore, reconstructing the deformation of satellite antennas and promptly correcting the phase of the output signals is crucial to ensure the performance of satellite communication. Fiber Bragg Grating (FBG) sensors have made significant progress in structural deformation reconstruction due to their sensitivity to deformation, small size, capability for multi-point measurements through serial connections, and immunity to electromagnetic interference. As the installation process can influence the sensing performance of FBG sensors, the author has developed FBG strain sensors and temperature sensors and designed an FBG deformation reconstruction system suitable for deformation measurements in variable temperature environments.Methods To achieve deformation reconstruction of satellite antennas using FBG sensors, we prepared FBG sensors using polyimide fiber gratings and conducted deformation reconstruction experiments on metal thin plates. Firstly, we analyzed the deformation field reconstruction algorithm based on discrete strain information on the structure surface. Subsequently, with the aid of a self-developed packaging device (Fig.4), we encapsulated the polyimide fiber Bragg gratings with non-metallic packaging materials, thereby preparing fiber Bragg grating strain sensors (Fig.2) and fiber Bragg grating temperature sensors (Fig.3) for deformation reconstruction. The layout of FBG sensors was analyzed using wavelength division multiplexing technology (Fig.6). FBG sensors were calibrated using equally strong cantilever beams and high-low temperature chambers (Fig.11). A three-dimensional deformation reconstruction test platform for simulating satellite antennas in variable temperature environments was built using the calibrated FBG sensors (Fig.7-8), and deformation reconstruction experiments were conducted under different temperatures and loads. To objectively evaluate the accuracy of sensor deformation reconstruction, the measurement values of a laser rangefinder were used as evaluation criteria to analyze the reconstruction accuracy of FBG sensors.Results and Discussions A non-metallic substrate-based FBG strain sensor and an FBG temperature sensor encapsulated in alumina ceramic were designed. A temperature-variable environment fiber Bragg grating (FBG) structural reconstruction system was established using these sensors, along with a grating demodulator and other equipment. The performance of different sensors demonstrated consistency and close sensitivity. The sensors are easy to install and suitable for engineering structural deformation monitoring applications.Conclusions The study describes the performance of FBG strain sensors packaged in flexible non-metallic substrates, exhibiting excellent consistency. The strain sensitivity and thermal response sensitivity of different FBG strain sensors are close. Calibration of the sensors reveals an average strain sensitivity of 0.835 pm/με, with a maximum deviation of 0.014 pm/με among different sensors at different stages. Calculating strain values from the FBG central wavelength and comparing them with strain values from a resistance strain gauge yields an average relative measurement error of 1.98% and a repeatability error of 0.52%. The average temperature sensitivity of FBG temperature sensors is 11.30 pm/°C, with a maximum temperature sensitivity deviation of 0.11 pm/°C among different sensors. Comparison between measured values of FBG temperature sensors and actual temperatures from a temperature chamber shows an average relative measurement error of 0.94% and a repeatability error of 0.54%. Utilizing the fabricated FBG sensors for strain reconstruction of aluminum alloy specimens and comparing them with a laser rangefinder, the reconstruction error of FBG does not exceed 5.94% at room temperature and 6.97% in a variable temperature environment..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240084 (2024)
Design and implementation of sliding correlation filtering algorithm for FBG reflectance spectra data
Jiayi MA, Xu ZHANG, Hong LI, Yunhong ZHU, and Mingli DONG
ObjectiveThe fiber Bragg grating sensing system, with its advantages of electromagnetic interference resistance, lightweight, and high-temperature resistance, has been widely used in structural health monitoring, aerospace, biomedical, and marine engineering fields. However, due to external factors, FBG reflected spectObjective The fiber Bragg grating sensing system, with its advantages of electromagnetic interference resistance, lightweight, and high-temperature resistance, has been widely used in structural health monitoring, aerospace, biomedical, and marine engineering fields. However, due to external factors, FBG reflected spectrum data often suffer from Gaussian noise, bad points, and baseline interference, leading to significant errors in central wavelength calculations. Although data filtering on the host computer software has good noise reduction effects, it is difficult to meet the real-time demodulation requirements in industrial applications. Moreover, the commonly used algorithms on the lower computer are limited by the measurement range, which cannot be applied to spectrum filtering of multiple abnormal reflections, and have low signal-to-noise ratio and poor key information extraction capabilities, as well as poor robustness.Methods To address the limitations of lower machine filtering algorithms, a novel FPGA-accelerated processing method for FBG reflection spectra, grounded in sliding correlation filtering, is proposed. The characteristics and origins of FBG abnormal reflection spectra are scrutinized, and the standard deviation of the second derivative of the Gaussian function is meticulously determined, predicated on the half-width of the FBG peak. The filter template length is calculated using sensor sampling compensation, and the negative values of the function are employed as the filter template weights. The spectrum data is correlated with the filter template through a sliding data window. A designed sliding correlation filtering processing module is crafted, and a devised circular queue strategy is employed to design storage memory. This crafted algorithm is implemented on the FPGA.Results and Discussions To assess the efficacy of the sliding correlation filtering algorithm in denoising various FBG abnormal reflection spectra, the algorithm was applied to process simulated signals containing varying levels of Gaussian noise, bad points, and baselines. The results were juxtaposed against those obtained from four other commonly employed lower machine filtering algorithms. The findings revealed that the sliding correlation filtering exhibited commendable key data extraction capabilities and robustness. Its suppression effect on Gaussian noise and baselines was markedly superior to that of other algorithms (Fig.4-5, Fig.8-9), with a maximum SNR improvement of 28.23 dB relative to other algorithms. The suppression effect of sliding correlation filtering on aberrant points was second only to that of median filtering and median averaging filtering (Fig.6-7), with a maximum SNR difference of no more than 3.14 dB. The mean deviation and standard deviation of the calculated central wavelength are the smallest, measuring 1.712 pm and 2.996 pm respectively. An experimental setup was established to collect the original FBG reflection spectra. The experiment (Fig. 14) underscored the algorithm's adeptness in rectifying FBG reflection spectra containing various abnormal conditions, while maintaining a low FPGA resource utilization rate (Tab.2). Remarkably, processing one spectral data point took a mere 5.09 μs.Conclusions This paper introduces a novel approach for processing FBG reflected spectra using FPGA, leveraging the sliding correlation filtering technique. The method ingeniously employs the negative of the second derivative of the Gaussian function as the weight of the filtering template, and meticulously performs correlation calculations between the reflected spectrum data and the filtering template through a sliding data window. The accelerated design of this algorithm is meticulously implemented on the FPGA platform. Experimental results demonstrate the efficacy of the proposed method in effectively correcting various abnormal FBG reflection spectra while preserving their fundamental data characteristics. It achieves a maximum SNR improvement of up to 28.23 dB compared to alternative algorithms, with the highest precision observed in central wavelength demodulation. The mean deviation and standard deviation of the central wavelength are reported as 1.712 pm and 2.996 pm, respectively. Additionally, the processing time for one data point is only 5.09 μs to process one data point. This research holds significant implications for engineering applications..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240103 (2024)
Optical Design
Research on bonding method of light detector assembly of space remote sensing camera
Jinhui LI, Yingbo ZHU, Shanshan CONG, and Lei ZHANG
ObjectiveThe core component of space remote sensing camera imaging is the detector, which is generally an image sensor and is fixed to the mechanical parts. The traditional fixed method of the detector is to use the pressing plate and other parts for mechanical fixing, which is easy to cause assembly stress, which willObjective The core component of space remote sensing camera imaging is the detector, which is generally an image sensor and is fixed to the mechanical parts. The traditional fixed method of the detector is to use the pressing plate and other parts for mechanical fixing, which is easy to cause assembly stress, which will affect the shape of the detector's sensitive surface and affect the imaging quality. However, for light detectors of small size, a bonding method can be designed to control the thickness of the adhesive layer to reduce the bonding force and ensure the structural strength after bonding.Methods The accuracy change of the detector by different bonding methods was analyzed by simulation combined with environmental test. Firstly, according to the working environment of the detector assembly, the appropriate adhesive is selected, the specific model is GHJ-01 optical epoxy adhesive and GD414 silicone rubber. Due to the different coefficient of thermal expansion of the bonded objects, the stress will be generated when the temperature changes. In order to reduce the stress, the thickness of the adhesive layer is determined to be 0.2 mm through the non-thermal bonding equation combined with the actual engineering calculation, and the bonding area is calculated to ensure the bonding strength. Six bonding schemes were proposed according to the parameters of the adhesive layer. The finite element simulation analysis was carried out on the detector components in the six schemes. The deformation of the key elements of the detector photosensitive surface was calculated and output, and several bonding schemes with small change of the detector photosensitive surface shape were obtained under the condition of temperature rise. After random vibration and high and low temperature cycle tests, optical splicing instrument and coordinate measuring instrument were used to detect the changes in detector splicing accuracy (including detector component straightness and detector flatness), and the optimal bonding scheme was obtained by comparing the test results.Results and Discussions The results of finite element simulation and environmental test are compared and analyzed. Firstly, by comparing the results of the finite element simulation analysis of six schemes, three bonding schemes are obtained under the condition of temperature rise, the shape change of the sensor's photosensitive surface is less than 0.001 2 mm. They are respectively GHJ-01 optical epoxy adhesive bonding bottom surface, GD414 silicone rubber bonding detector bottom and side surface, and GD414 silicone rubber bonding detector bottom and side with GHJ-01 optical epoxy adhesive top dispensing. The test results after vibration test and high and low temperature test show that GD414 silicone rubber is used to bond the bottom and side of the detector, and GHJ-01 optical epoxy adhesive top dispensing scheme can ensure that the surface shape accuracy of the detector assembly is better than 0.000 7 mm and the linear accuracy is better than 0.001 mm under the condition of 200 ℃ temperature rise and mechanical vibration.Conclusions Through the simulation and environmental verification of different schemes, the conclusion is drawn by analyzing the accuracy change of the detector’s photosensitive surface. For small and light detectors, GD414 silicone rubber is used to bond the bottom and side of the detector, and GHJ-01 optical epoxy glue at the top can reduce the thermal stress of the adhesive layer, maintain the sensor's photosensitive surface shape, and meet the bonding structural strength of the light detector and meet the requirements of detector assembly splicing accuracy..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240065 (2024)
Freeform surface design method for correcting distortion of large-field-of-view coaxial optical systems
Yan DING, Naiwen ZHANG, Chao YANG, and Changxi XUE
ObjectiveWith the continuous advancement of optical design and optical manufacturing technology, the performance of optical systems has also been significantly improved. The increase in the field of view is particularly noticeable. However, an increase in the field of view can lead to an increase in the problem of distObjective With the continuous advancement of optical design and optical manufacturing technology, the performance of optical systems has also been significantly improved. The increase in the field of view is particularly noticeable. However, an increase in the field of view can lead to an increase in the problem of distortion. It is often difficult to correct distortion at the late stage of optical design using optical design software, so it is necessary to study the correction of distortion in optical systems with large fields of view. Freeform surfaces can be used to correct distortion in optical systems due to their large degree of freedom, but current correction methods often utilize aspherical surfaces converted to freeform surfaces, which are weak, cannot correct every field of view, and have uncontrollable surface shapes. Therefore, it is necessary to develop a freeform surface design method for correcting distortion in large-field-of-view coaxial optical systems to minimize the problems of the above design methods.Methods A freeform lens is designed on the premise of the original system, which is inserted into the original optical system as a subsequently added field lens, and optimized as the initial structure for the next step to ultimately achieve the purpose of correcting distortion. Firstly, we analyze the indexes of the original system, and extract the pupil position and image plane information as the starting and ending points. Then the main ray of each field of view after pupil exit is deflected by ray tracing (Fig.3), and the deflection is based on the law of vector refraction (Fig.4). Then the feature data points are calculated based on the point-by-point construction method (Fig.5), and since this process is carried out in a two-dimensional coordinate system, a coordinate transformation scheme is given. Finally, based on the three-dimensional coordinate points, the data are fitted based on XY polynomial freeform surfaces, which in turn gives the freeform coefficients.Results and Discussions Based on the above design methodology, verification and simulation were carried out using optical design software. The original system of the design was chosen as the vehicle optical system, and the results and discussions were carried out after slightly adjusting it as the original system. Freeform surfaces and aspherical surfaces were fitted as comparisons (Fig.12), and the final design architecture was given (Fig.11). Three comparative studies of the simulation results were performed. In terms of SMIA-TV distortion (Fig.13), MTF (Fig.15(a)-(b)), and Monte Carlo analysis (Tab.2), the freeform surfaces designed by this method showed different degrees of improvement compared to the original system and the aspherical surfaces, and the freeform surfaces and the aspherical surfaces showed the same degree of decrease in the relative illumination compared to the original system.Conclusions A freeform surface design method is proposed for correcting distortion in large-field-of-view coaxial optical systems at the later stage of optical design. By analyzing the indicators of the original system, the starting point coordinates, the characteristic ray and the end point coordinates, as well as the main ray emanating from the original system are extracted. The ray tracing is utilized to deflect the system based on the point-by-point method and the law of vector refraction for the purpose of distortion correction. The coordinate conversion scheme and data point fitting method are given based on XY polynomial freeform surfaces. Examples are then designed to verify the correctness of this method, comparing the system with the freeform lens with the original system and the system with the aspherical lens in various ways. The TV distortion, relative illumination, average modulation transfer function at one-half Nyquist frequency, and 90% probability average modulation transfer function at one-quarter Nyquist frequency of the original system are -6.335 5%, 65.5%, 0.54, and 0.574, respectively; The results of the system with the addition of an aspherical lens are -0.2111%, 50.2%, 0.58, and 0.587; And the results of the system with the addition of a freeform lens are 0.000 2%, 50%, 0.64, and 0.589, respectively. After analyzing the results, it is found that this design method can effectively correct the distortion problem brought by the large field of view to the coaxial optical system. However, the correction of distortion is at the expense of the relative illuminance index. The modulation transfer function of the optical system can also be improved with redundant degrees of freedom. Compared with aspherical surfaces, freeform surfaces have greater advantages in correcting distortion than aspherical surfaces at the same location..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240077 (2024)
Design of harmonic diffraction structure in glasses-free three-dimensional display with high brightness and low chromatic
Fuguo LYU, Furong HUO, and Changxi XUE
ObjectiveDue to the inability of flat display technology to meet people's desire to perceive three-dimensional depth information, and the inability of bulky display devices in head mounted 3D display products to meet portability requirements, glasses-free 3D (three-dimensional)display technology has become a highlyObjective Due to the inability of flat display technology to meet people's desire to perceive three-dimensional depth information, and the inability of bulky display devices in head mounted 3D display products to meet portability requirements, glasses-free 3D (three-dimensional)display technology has become a highly promising development direction. Although significant progress has been made in the development of glasses-free 3D displays based on cylindrical barriers or microlens arrays utilizing the principles of geometric optics. However, the inherent defects of geometric optics lead to issues such as reduced image brightness, poor fusion performance, and significant waste of pixel resources. In contrast, the glasses-free 3D display technology based on diffraction optics has largely solved these problems. At present, the implementation methods using diffraction gratings and traditional diffraction optical elements still exhibit drawbacks such as low brightness, significant color difference, and complex design and manufacturing processes. Therefore, in order to improve light efficiency and image clarity, and reduce design and manufacturing difficulties, a phase modulation panel has been designed. By aligning the array of harmonic diffraction subunits with the pixel level of the LCD panel, a good glasses-free 3D visual experience can be provided.Methods A phase modulation panel consisting of four interleaved arrays of harmonic diffraction subunits was designed. In TracePro software, nearly 10 000 light rays were vertically incident on two individual pixels located in the horizontal direction of the phase modulation panel to verify the convergence effect of light rays (Fig.2), simplifying the complexity of designing and manufacturing harmonic diffraction structures. To meet the binocular parallax attribute, a display effect with a 32 mm horizontal interval for dual views and uniform distribution of four viewpoints has been achieved. At the same time, the effect of oblique incidence of light sources on the total luminous efficiency was studied under different step approximations (Tab.3).Results and Discussions Compared with ordinary diffraction structures that require three RGB diffraction subunits, harmonic diffraction optical elements have the same optical power and high diffraction efficiency at multiple high diffraction levels, and can use the same harmonic diffraction structure to modulate the three RGB outgoing rays, thereby reducing design complexity and manufacturing difficulty, improving optical efficiency and image clarity. Within the range of 384.2-402.8 mm, bright color 3D parallax images can be seen over a length of approximately 18.6 mm. In addition, when the incident angle is 0°, the total luminous efficiency of the 16th order approximate harmonic diffraction microstructure can reach 60.65%, and there is little change in the total luminous efficiency when the incident angle is within 10°. By combining with LCD display panels to achieve pixel by pixel light modulation, a naked eye 3D display system with high brightness, low color difference, and low design and manufacturing difficulty is ultimately obtained.Conclusions Due to the characteristics of harmonic diffraction optical elements having the same focal length and high diffraction efficiency at multiple high diffraction levels, a phase modulation panel consisting of four interlaced arrays of discrete harmonic diffraction subunits was designed. Combined with a 4.3-inch (1 inch=2.54 cm)LCD panel with 800 pixel×480 pixel resources, the display effect of a horizontal four point distribution with a horizontal spacing of 32 mm and a single image resolution of 400×240 was achieved. By modulating the three outgoing RGB rays through the same harmonic diffraction structure, the design complexity and manufacturing difficulty are reduced. The light modulation effect of two individual pixels in the horizontal direction of the phase modulation panel was simulated using Tracepro software at three harmonic wavelengths of R=638.4 nm, G=532.0 nm, and B=456.0 nm. This provides a simple verification method for the light modulation effect of the entire phase modulation panel. Finally, a naked eye 3D display effect was obtained with two viewing angles, a viewing angle interval of approximately 9.4°, the optimal viewing position being approximately 384.2-402.8 mm away from the screen, and the optimal viewing range being approximately 18.6 mm. In addition, considering the difficulty of manufacturing and design, it is determined that the incident angle of the light source should be less than 10° to ensure a total luminous efficiency of over 60% at the 16th order approximation. The simulation results show that the designed harmonic diffraction structure has the characteristics of low processing difficulty, high design degrees of freedom, and strong optical modulation ability..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240097 (2024)
Spectroscopy
Study on temperature inversion of deflagration spectrum of pyrotechnics
Meng ZHAO, Huijun XIA, Ruize CHAO, Ming SHAO, Xiangzheng CHENG, Lanshuang LU, Zheng QIU, Haimeng LIU, and Yong TAN
ObjectiveAccurate temperature measurement under high temperature, high pressure, and high radiation conditions is always a difficult task. To address this challenge, we realize the non-contact temperature measurement of multi-component pyrotechnic composition deflagration process based on the radiation spectral temperaObjective Accurate temperature measurement under high temperature, high pressure, and high radiation conditions is always a difficult task. To address this challenge, we realize the non-contact temperature measurement of multi-component pyrotechnic composition deflagration process based on the radiation spectral temperature measurement technology, providing basic parameters for further defining the reaction steps and deflagration products of pyrotechnic compositions.Methods By establishing the radiation spectral temperature retrieval model of multi-component pyrotechnic compositions and temperature indicating particles, a calculation method based on the emissivity of small condensed phase gray-body particles is given, and the radiation spectrum of the condensed phase particles is obtained by experiment to retrieve the temperature as indicated by the continuous thermal radiation spectrum. In order to improve the temperature retrieval accuracy, we propose an improved method to reduce the influence of ion peak broadening during the deflagration of multi-component pyrotechnic compositions by using the Wien transformation to analyze the spectral curve, we also use double square weighted fitting by combining the Bisquare algorithm and the least squares algorithm to remove the non-thermal radiation spectral lines to improve the accuracy of the retrieved temperature variation curve. This method provides a fast and anti-interference way for non-contact spectral temperature retrieval under specific conditions.Results and Discussions The detonation of pyrotechnic agents mainly involves two exothermic processes. The first process is: under initial conditions, the oxidant and reducing agent undergo a violent reaction and generate a large amount of heat, and the pyrotechnic agent undergoes instantaneous detonation, with an instantaneous temperature rise to 2795 K; Afterwards, the temperature gradually decreased and a brief uniform distribution of temperature appeared around 25 ms, and before 100 ms, the temperature uniformly decreased to 1485 K. The second process followed by a second increase in temperature, which is analyzed to be due to the presence of cellulose, lignin, and unburned particulate dust in the charcoal that have not been thermally decomposed in the first stage. Under continuous heating conditions, surface carbonization cracks appear and cause combustion to release a large amount of heat. When the accumulated energy exceeds a certain critical value, intense combustion occurs, resulting in a second exothermic peak. After 150 ms, the secondary exothermic reaction had ended, and most of the carbon particles were consumed through secondary deflagration. The thermal radiation spectrum mainly came from alumina temperature indicating particles, and their good thermal conductivity led to a rapid decrease in system temperature, which was significantly faster than the first temperature decrease process.Conclusions The entire temperature change process during the detonation of pyrotechnic agents exhibits a secondary exothermic phenomenon of a characteristic pattern of heating, cooling, reheating, and final cooling. This article determines whether there are non thermal radiation spectral lines based on the line shape and dispersion degree of the spectral lines, and adds weight coefficients of the Bisquare algorithm to improve the anti-interference ability of inversion to ion peaks and noise. It provides a new inversion idea and method for detecting temperature changes in the temperature field of pyrotechnic explosive detonation. This method can detect and analyze the secondary heating phenomenon in the detonation of pyrotechnic agents..
Infrared and Laser Engineering
- Publication Date: Jun. 25, 2024
- Vol. 53, Issue 6, 20240114 (2024)
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