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RSS2022 Vol. 46, No. 1
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[Abstract]
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2022, 46(1): 1-37.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.001
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Abstract:
At the beginning of the 21st century, GOL'TSMAN et al. started the research field of superconducting nanowire single photon detector (SNSPD). After researches and developments in the past twenty years, SNSPDs have become a type of single-photon detectors with unprecedented comprehensive performances, and have been applied in quantum and classical faint-light detection. In this paper, the important researches and developments of SNSPDs in the past twenty years were reviewed from the following nine aspects: Performance metrics, device physics, superconducting films, device structures, fabrication, optical coupling, electronic readouts, cryogenic systems, and applications. Then, the future directions for research and development were discussed.
At the beginning of the 21st century, GOL'TSMAN et al. started the research field of superconducting nanowire single photon detector (SNSPD). After researches and developments in the past twenty years, SNSPDs have become a type of single-photon detectors with unprecedented comprehensive performances, and have been applied in quantum and classical faint-light detection. In this paper, the important researches and developments of SNSPDs in the past twenty years were reviewed from the following nine aspects: Performance metrics, device physics, superconducting films, device structures, fabrication, optical coupling, electronic readouts, cryogenic systems, and applications. Then, the future directions for research and development were discussed.
2022, 46(1): 38-44.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.002
Abstract:
Spontaneous parametric down-conversion (SPDC) is a primary method for preparing quantum light sources. In this paper, the central technical schemes of different types of SPDC (type-0, type-Ⅰ, type-Ⅱ) were introduced, and the research progress and applications of quantum light sources to prepare multi-photon quantum entangled states and high-dimensional quantum entangled states were discusseed. At the same time, the preparation and application of narrow linewidth entangled states from cavity-enhanced SPDC were also introduced. Finally, the existing problems and future development direction of various schemes were analyzed and prospected.
Spontaneous parametric down-conversion (SPDC) is a primary method for preparing quantum light sources. In this paper, the central technical schemes of different types of SPDC (type-0, type-Ⅰ, type-Ⅱ) were introduced, and the research progress and applications of quantum light sources to prepare multi-photon quantum entangled states and high-dimensional quantum entangled states were discusseed. At the same time, the preparation and application of narrow linewidth entangled states from cavity-enhanced SPDC were also introduced. Finally, the existing problems and future development direction of various schemes were analyzed and prospected.
2022, 46(1): 45-57.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.003
Abstract:
Quantum internet is an important basis for realizing multi-party quantum communication, distributed quantum computing, and other quantum information technologies. Quantum memory, as a significant part for realizing Internet, plays a pivotal role in the development and application of quantum information technology. Nowadays, the global optical fiber network has become a powerful carrier of information transmission, and quantum memory in communication band is highly valued because it is easy to be embedded in the current optical fiber network. Focus on telecom band optical quantum memory with rare earth ions doped solid-state system, the basic principle of rare earth ions doped solid-state quantum memory was firstly introduced, including rare earth doped material properties and memory protocol. the current state of the art was then introduced. Finally, a brief analysis on its future development trend was given, and the prospect for the construction of quantum Internet was made.
Quantum internet is an important basis for realizing multi-party quantum communication, distributed quantum computing, and other quantum information technologies. Quantum memory, as a significant part for realizing Internet, plays a pivotal role in the development and application of quantum information technology. Nowadays, the global optical fiber network has become a powerful carrier of information transmission, and quantum memory in communication band is highly valued because it is easy to be embedded in the current optical fiber network. Focus on telecom band optical quantum memory with rare earth ions doped solid-state system, the basic principle of rare earth ions doped solid-state quantum memory was firstly introduced, including rare earth doped material properties and memory protocol. the current state of the art was then introduced. Finally, a brief analysis on its future development trend was given, and the prospect for the construction of quantum Internet was made.
2022, 46(1): 58-63.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.004
Abstract:
In order to calibrate the number of photons contained in the unknown pulse, the signal difference of the system output was measured when the light pulses with different photon numbers were under microwave kinetic inductance detector (MKID) effect in the superconducting environment. The average interval method and iterative method were adopted, and the theoretical analysis and experimental verification were carried out. The results show that, the number of photons of unknown 1550nm single-pulse light in the cryogenic measurement system can be identified by MKID. After data processing, the average photon numbers were 1.98 and 1.81 respectively. Among them, the process of calibrating the number of photons by the average interval method is relatively simple, and the iterative method needs to be further explored. It is helpful for single-pulse photon number detection.
In order to calibrate the number of photons contained in the unknown pulse, the signal difference of the system output was measured when the light pulses with different photon numbers were under microwave kinetic inductance detector (MKID) effect in the superconducting environment. The average interval method and iterative method were adopted, and the theoretical analysis and experimental verification were carried out. The results show that, the number of photons of unknown 1550nm single-pulse light in the cryogenic measurement system can be identified by MKID. After data processing, the average photon numbers were 1.98 and 1.81 respectively. Among them, the process of calibrating the number of photons by the average interval method is relatively simple, and the iterative method needs to be further explored. It is helpful for single-pulse photon number detection.
2022, 46(1): 64-68.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.005
Abstract:
In order to solve the technical bottleneck of the sensitive detection of the optically detected magnetic resonance (ODMR) signal from the nitrogen vacancy (NV) color centers in the diamond by taking the advantage of the directional amplification of stimulated radiation, an optical amplification system was set up to investigate the stimulated radiation of NV color centers in diamond, where the maximum amplification efficiency reached 10.5%. Besides, it is found that the amplification efficiency is related to the pump laser power and signal laser power as well as the polarization states of the two lasers. The results show that it is promising to use the amplification of stimulated radiation to replace the fluorescence in the ODMR measurement with NV color centers in the application of remote sensing.
In order to solve the technical bottleneck of the sensitive detection of the optically detected magnetic resonance (ODMR) signal from the nitrogen vacancy (NV) color centers in the diamond by taking the advantage of the directional amplification of stimulated radiation, an optical amplification system was set up to investigate the stimulated radiation of NV color centers in diamond, where the maximum amplification efficiency reached 10.5%. Besides, it is found that the amplification efficiency is related to the pump laser power and signal laser power as well as the polarization states of the two lasers. The results show that it is promising to use the amplification of stimulated radiation to replace the fluorescence in the ODMR measurement with NV color centers in the application of remote sensing.
2022, 46(1): 69-78.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.006
Abstract:
Nonlocal dispersion cancellation is one of the non-classical effects of quantum entangled photon sources, and it has important applications in quantum information science. A detailed introduction to the concept, research significance of nonlocal dispersion cancellation, and the research progress in China and abroad in recent years were reviewed. The following three cases: the nonlocal dispersion cancellation of frequency entangled photon sources, the nonlocal dispersion cancellation in Franson interferometers, and the local dispersion cancellation in the Hong-Ou-Mandel interferometer were then compared and analyzed. On this basis, the prospects for the study of quantum dispersion cancellation were anticipated.
Nonlocal dispersion cancellation is one of the non-classical effects of quantum entangled photon sources, and it has important applications in quantum information science. A detailed introduction to the concept, research significance of nonlocal dispersion cancellation, and the research progress in China and abroad in recent years were reviewed. The following three cases: the nonlocal dispersion cancellation of frequency entangled photon sources, the nonlocal dispersion cancellation in Franson interferometers, and the local dispersion cancellation in the Hong-Ou-Mandel interferometer were then compared and analyzed. On this basis, the prospects for the study of quantum dispersion cancellation were anticipated.
2022, 46(1): 79-84.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.007
Abstract:
In order to improve the efficiency of quantum secure transmission, the properties of n-particle Greenberger-Horne-Zeilinger(GHZ) state were used to study the quantum secure direct communication (QSDC) with single photon mixture. The implementation process of communication was designed. The transmission efficiency, quantum bit utilization, and coding capacity of communication were discussed, and its security was theoretically analyzed. Compared with other classical QSDC protocols, the results show that the coding capacity and the transmission efficiency can be respectively improved to (n+1)bit and 200% with this scheme. Security analysis shows that the protocol can resist interception and measurement retransmission attacks, Trojan horse attacks, denial of service attacks, auxiliary particle attacks and entanglement attacks.
In order to improve the efficiency of quantum secure transmission, the properties of n-particle Greenberger-Horne-Zeilinger(GHZ) state were used to study the quantum secure direct communication (QSDC) with single photon mixture. The implementation process of communication was designed. The transmission efficiency, quantum bit utilization, and coding capacity of communication were discussed, and its security was theoretically analyzed. Compared with other classical QSDC protocols, the results show that the coding capacity and the transmission efficiency can be respectively improved to (n+1)bit and 200% with this scheme. Security analysis shows that the protocol can resist interception and measurement retransmission attacks, Trojan horse attacks, denial of service attacks, auxiliary particle attacks and entanglement attacks.
2022, 46(1): 85-93.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.008
Abstract:
In order to realize the focusing function of the dielectric metasurface and the adjustment of the phase of the light field, the geometric phase modulation principle was used to design the micro-element structure and spatial distribution. Using SiO2 as the substrate and the hexagonal unit cell of sub-wavelength TiO2 elliptical cylinder as the basic structure, a metalens with a parabolic gradient distribution of phase mutation was designed, which was suitable for the wavelength range of 480nm to 580nm. Based on this structure, theoretical analysis and experimental verification were carried out. It is found that for the linearly polarized light with this structure, the normalized full width at half maximum of the focus is about 428nm, and the full width at half maximum obtained by focusing on vector light is about 258nm, which is better than that of the linearly polarized light. The focusing characteristics of the 3rd-order and 4th-order Ince-Gaussian vector light field after passing through the metasurface were studied, and the basic spatial structure of the focusing field can maintain the incident vector light field, but the center structure information will be lost. That is, the Ince-Gaussian vector vortex light field will show a broken spatial structure after focusing due to the existence of the vortex phase. The results show that the matching degree between the metasurface structure and the incident light field vector structure is an important factor affecting the focusing characteristics. This research provides a reference for understanding the metasurface focusing mechanism of complex vector light fields.
In order to realize the focusing function of the dielectric metasurface and the adjustment of the phase of the light field, the geometric phase modulation principle was used to design the micro-element structure and spatial distribution. Using SiO2 as the substrate and the hexagonal unit cell of sub-wavelength TiO2 elliptical cylinder as the basic structure, a metalens with a parabolic gradient distribution of phase mutation was designed, which was suitable for the wavelength range of 480nm to 580nm. Based on this structure, theoretical analysis and experimental verification were carried out. It is found that for the linearly polarized light with this structure, the normalized full width at half maximum of the focus is about 428nm, and the full width at half maximum obtained by focusing on vector light is about 258nm, which is better than that of the linearly polarized light. The focusing characteristics of the 3rd-order and 4th-order Ince-Gaussian vector light field after passing through the metasurface were studied, and the basic spatial structure of the focusing field can maintain the incident vector light field, but the center structure information will be lost. That is, the Ince-Gaussian vector vortex light field will show a broken spatial structure after focusing due to the existence of the vortex phase. The results show that the matching degree between the metasurface structure and the incident light field vector structure is an important factor affecting the focusing characteristics. This research provides a reference for understanding the metasurface focusing mechanism of complex vector light fields.
2022, 46(1): 94-98.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.009
Abstract:
In order to solve the problem of laser laminated lap welding of galvanized sheet for automobile body, a process of rolling a certain exhaust passage on the laminated joint surface of galvanized sheet was put forward, so that a better welding effect could be obtained under zero clearance. The welding quality of zero-gap laminated joints with and without exhaust channels was compared and analyzed from the aspects of weld surface morphology, splash generation, weld microstructure, micro-hardness, and mechanical properties of joints. The results show that the composite exhaust channel with the main exhaust channel depth of 125.0μm and the secondary exhaust channel depth of 32.6μm can be obtained by rolling, and the lap joint with satisfactory appearance and mechanical properties can be obtained at laser power of 2500W and scanning speed of 25mm/s. The research is helpful to improve the laser overlay welding process of body galvanized sheet.
In order to solve the problem of laser laminated lap welding of galvanized sheet for automobile body, a process of rolling a certain exhaust passage on the laminated joint surface of galvanized sheet was put forward, so that a better welding effect could be obtained under zero clearance. The welding quality of zero-gap laminated joints with and without exhaust channels was compared and analyzed from the aspects of weld surface morphology, splash generation, weld microstructure, micro-hardness, and mechanical properties of joints. The results show that the composite exhaust channel with the main exhaust channel depth of 125.0μm and the secondary exhaust channel depth of 32.6μm can be obtained by rolling, and the lap joint with satisfactory appearance and mechanical properties can be obtained at laser power of 2500W and scanning speed of 25mm/s. The research is helpful to improve the laser overlay welding process of body galvanized sheet.
2022, 46(1): 99-109.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.010
Abstract:
As a new high speed underwater wireless communication technology, underwater wireless optical communication (UWOC) plays an important role in marine ecological environment monitoring, resource exploration, and military operations, and has become a key technology for competition all over the world. Three kinds of underwater wireless communication modes were compared, the channel characteristics of UWOC were introduced, and the research progress of key technologies such as light source, modulation, channel coding, and detection in UWOC system were described in detail. At the same time, the development trend of UWOC technology was summarized, which provides a reference for further research and practical application of UWOC system in the future.
As a new high speed underwater wireless communication technology, underwater wireless optical communication (UWOC) plays an important role in marine ecological environment monitoring, resource exploration, and military operations, and has become a key technology for competition all over the world. Three kinds of underwater wireless communication modes were compared, the channel characteristics of UWOC were introduced, and the research progress of key technologies such as light source, modulation, channel coding, and detection in UWOC system were described in detail. At the same time, the development trend of UWOC technology was summarized, which provides a reference for further research and practical application of UWOC system in the future.
2022, 46(1): 110-119.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.011
Abstract:
Carbon fiber reinforced plastics (CFRP) has broad application prospects in aerospace, national defense, and other fields due to its excellent performance. In order to master the removal mechanism of laser processing CFRP, and to developed a high efficiency, low damage processing method of the material, the researches of the removal mechanism of CFRP by laser processing were reviewed. The progress of laser processing CFRP materials at domestic and abroad was introduced from the aspects of laser characteristics, process parameters, gas-liquid assistance and material properties. The factors affecting the quality of laser processing CFRP were summarized. Some suggestions to improving the processing quality were proposed. Finally, the development trend of laser processing CFRP was prospected.
Carbon fiber reinforced plastics (CFRP) has broad application prospects in aerospace, national defense, and other fields due to its excellent performance. In order to master the removal mechanism of laser processing CFRP, and to developed a high efficiency, low damage processing method of the material, the researches of the removal mechanism of CFRP by laser processing were reviewed. The progress of laser processing CFRP materials at domestic and abroad was introduced from the aspects of laser characteristics, process parameters, gas-liquid assistance and material properties. The factors affecting the quality of laser processing CFRP were summarized. Some suggestions to improving the processing quality were proposed. Finally, the development trend of laser processing CFRP was prospected.
2022, 46(1): 120-124.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.012
Abstract:
In order to achieve the purpose of measuring the height change of the liquid, the method based on the multimode interference effect of the hollow core fiber was used to study the change of the interference spectrum caused by the multimode interference of the light source in the hollow core fiber under the influence of the external medium. The liquid level sensing experiment of the multimode interference effect in the core optical fiber was carried out. The relationship between the interference spectrum of the liquid level sensor and the change of the liquid level and the influence of liquids with different refractive indexes on the measurement results were experimentally studied, and the experimental errors were analyzed. The results show that the liquid level measurement range of the fiber optic liquid level sensor is 0mm~55mm, when the liquid refractive index is 1.33 and 1.35, the liquid level measurement sensitivity is 0.180nm/mm and 0.224nm/mm, respectively. It is more accurate and feasible to use a sensor with a single-mode-air-core-single-mode structure to measure liquid level changes.
In order to achieve the purpose of measuring the height change of the liquid, the method based on the multimode interference effect of the hollow core fiber was used to study the change of the interference spectrum caused by the multimode interference of the light source in the hollow core fiber under the influence of the external medium. The liquid level sensing experiment of the multimode interference effect in the core optical fiber was carried out. The relationship between the interference spectrum of the liquid level sensor and the change of the liquid level and the influence of liquids with different refractive indexes on the measurement results were experimentally studied, and the experimental errors were analyzed. The results show that the liquid level measurement range of the fiber optic liquid level sensor is 0mm~55mm, when the liquid refractive index is 1.33 and 1.35, the liquid level measurement sensitivity is 0.180nm/mm and 0.224nm/mm, respectively. It is more accurate and feasible to use a sensor with a single-mode-air-core-single-mode structure to measure liquid level changes.
2022, 46(1): 125-128.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.013
Abstract:
In order to quickly expose vegetation camouflage and transform the hyperspectral research problem into the multi-spectral application problem, the hyperspectral band was selected based on the Relief-F algorithm was selected for the study of vegetation camouflage. First, the common plant spruce was used to simulate vegetation camouflage targets, and the HH2 ground-object spectrometer was used to collect experimental data. Then, the author introduced the Relief-F algorithm to screen the subset of feature bands, and conducted classification experiments with the subset of band obtained by other two common algorithms.The results show that the classification accuracy of using the Relief-F algorithm to choose the feature band subset is up to 96.4%, which is higher than the other two algorithms. This research is helpful for exposing the camouflage problem of vegetation.
In order to quickly expose vegetation camouflage and transform the hyperspectral research problem into the multi-spectral application problem, the hyperspectral band was selected based on the Relief-F algorithm was selected for the study of vegetation camouflage. First, the common plant spruce was used to simulate vegetation camouflage targets, and the HH2 ground-object spectrometer was used to collect experimental data. Then, the author introduced the Relief-F algorithm to screen the subset of feature bands, and conducted classification experiments with the subset of band obtained by other two common algorithms.The results show that the classification accuracy of using the Relief-F algorithm to choose the feature band subset is up to 96.4%, which is higher than the other two algorithms. This research is helpful for exposing the camouflage problem of vegetation.
2022, 46(1): 129-133.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.014
Abstract:
In order to reduce the interference of noise in laser Doppler vibration signal, a laser Doppler vibration signal processing method based on improved wavelet de-noising was proposed. The scale was introduced into the threshold function, and a new evaluation index was established to select the optimal decomposition level. The improved algorithm was used to process the vibration signal. The improved algorithm and the original algorithm were adopted for processing the vibration signal. The simulation analysis and experimental verification were then carried out, and the vibration data before and after processing were obtained. The results indicate that the signal-to-noise ratio of simulated signals processed by the improved algorithm is 19.4% higher than that of the original soft and hard threshold algorithm. The measured tuning fork vibration frequency is 515Hz, which is consistent with the actual tuning fork frequency. This result is helpful to reduce the influence of noise in the laser Doppler vibration signal and obtain the vibration state.
In order to reduce the interference of noise in laser Doppler vibration signal, a laser Doppler vibration signal processing method based on improved wavelet de-noising was proposed. The scale was introduced into the threshold function, and a new evaluation index was established to select the optimal decomposition level. The improved algorithm was used to process the vibration signal. The improved algorithm and the original algorithm were adopted for processing the vibration signal. The simulation analysis and experimental verification were then carried out, and the vibration data before and after processing were obtained. The results indicate that the signal-to-noise ratio of simulated signals processed by the improved algorithm is 19.4% higher than that of the original soft and hard threshold algorithm. The measured tuning fork vibration frequency is 515Hz, which is consistent with the actual tuning fork frequency. This result is helpful to reduce the influence of noise in the laser Doppler vibration signal and obtain the vibration state.
2022, 46(1): 134-138.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.015
Abstract:
In order to realize the power line extraction of long distance linear airborne light detection and ranging(LiDAR), a power line extraction method of long-distance airborne LiDAR based on cloth simulation was proposed. On the basis of data preprocessing, the function between cloth and corresponding airborne LiDAR point cloud was analyzed by simulating the falling process of cloth. The position where cloth stayed after gravity falling was determined as the power line point cloud with similar height, and then the straight line was fitted in the xOy plane. The distances from points to the fitting line were used to judge the number of power lines whether odd or even. And the power line point clouds were divided by the judgment of points on both sides of the line to achieve the extraction of a single power line. The experimental results show that the accuracy of the proposed method is 98.9%, with high degree of automation and not sensitive to the lack of local point cloud, which has good engineering application value for intelligent powerline inspection and automatic analysis of transmission channel spatial structure.
In order to realize the power line extraction of long distance linear airborne light detection and ranging(LiDAR), a power line extraction method of long-distance airborne LiDAR based on cloth simulation was proposed. On the basis of data preprocessing, the function between cloth and corresponding airborne LiDAR point cloud was analyzed by simulating the falling process of cloth. The position where cloth stayed after gravity falling was determined as the power line point cloud with similar height, and then the straight line was fitted in the xOy plane. The distances from points to the fitting line were used to judge the number of power lines whether odd or even. And the power line point clouds were divided by the judgment of points on both sides of the line to achieve the extraction of a single power line. The experimental results show that the accuracy of the proposed method is 98.9%, with high degree of automation and not sensitive to the lack of local point cloud, which has good engineering application value for intelligent powerline inspection and automatic analysis of transmission channel spatial structure.
2022, 46(1): 139-142.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.016
Abstract:
The large numerical aperture and high resolution mobile phone lens using the plastic asphere lenses E48R and LEXANH is demanded with the development of mobile phone market. A kind of large numerical aperture and high resolution mobile phone lens was designed by using Code-v optical design software. The mobile phone lens is constituted by five plastic asphere lenses, an infrared cut filter, and a sensor cover glass. The first and fourth lenses are positive lenses. The second, third, and fifth lenses are negative lenses. Design results show that when the space frequency is 350lp/mm, the modulation transfer function (MTF) of all field of view are more than 0.2, and the MTF of 0.7 field of view are more than 0.34. The field curves are less than 0.02mm, and the distortion are less than 2.55%. It provides a reference value for similar systems.
The large numerical aperture and high resolution mobile phone lens using the plastic asphere lenses E48R and LEXANH is demanded with the development of mobile phone market. A kind of large numerical aperture and high resolution mobile phone lens was designed by using Code-v optical design software. The mobile phone lens is constituted by five plastic asphere lenses, an infrared cut filter, and a sensor cover glass. The first and fourth lenses are positive lenses. The second, third, and fifth lenses are negative lenses. Design results show that when the space frequency is 350lp/mm, the modulation transfer function (MTF) of all field of view are more than 0.2, and the MTF of 0.7 field of view are more than 0.34. The field curves are less than 0.02mm, and the distortion are less than 2.55%. It provides a reference value for similar systems.
2022, 46(1): 143-148.
doi: 10.7510/jgjs.issn.1001-3806.2022.01.017
Abstract:
The high reflection film of large aperture mirror is an important optical element in the optical system of large aperture space camera. In order to observe more targets and obtain more earth and space observation information, higher requirements were put forward for the retro reflective film of large aperture space camera. It was necessary to have a wider working spectrum and higher reflectivity toimprove the optical performance of the substrate and to reduce the influence of space environment on the performance of the high reflection film and the stress of the film. In this paper, the achievements in the research of high reflective film for large aperture space camera mirrors at home and abroad in recent years were reviewed. The review shows that, although there are still many difficulties in the design and manufacture of high reflection film, with the deepening of research and the proposal of new methods, the solutions to these difficulties have been basically found.
The high reflection film of large aperture mirror is an important optical element in the optical system of large aperture space camera. In order to observe more targets and obtain more earth and space observation information, higher requirements were put forward for the retro reflective film of large aperture space camera. It was necessary to have a wider working spectrum and higher reflectivity toimprove the optical performance of the substrate and to reduce the influence of space environment on the performance of the high reflection film and the stress of the film. In this paper, the achievements in the research of high reflective film for large aperture space camera mirrors at home and abroad in recent years were reviewed. The review shows that, although there are still many difficulties in the design and manufacture of high reflection film, with the deepening of research and the proposal of new methods, the solutions to these difficulties have been basically found.
