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Optical Design and Fabrication|349 Article(s)
Novel Design of Athermal and Rigid Support Structure for Small- and Medium-Aperture Mirrors
Jian Yuan, and Lei Zhang
A novel rigid support structure is proposed in this paper to solve the contradiction between thermal stability and structural stiffness in small- and medium-aperture space mirrors assembled using traditional flexible supports. Additionally, a high-precision secondary mirror assembly with a clear aperture of ?214 mm is developed for a high-resolution space camera. The combination of a mirror body, cone, support cylinder, and rigid base plate is adopted to realize heat dissipation by extending and optimizing the transmission path of the thermal stress within the assembly. The secondary mirror assembly with a rigid support structure weighs 2.6 kg, and the surface accuracy change has a root-mean-square (RMS) value of 2.573 nm in the simulation under the condition of a 4 °C uniform temperature rise. The inclination and displacement of the mirror body subjected to the gravity test are 2.028" and 0.566 μm, respectively, revealing the outstanding advantages of the proposed scheme over traditional flexible support systems. The measured surface accuracy RMS value of the secondary mirror is 0.0181λ (λ=632.8 nm), and the changes in the surface accuracy at 16 and 24 °C do not exceed 0.0025λ. The fundamental frequency of the assembly reaches 502.1 Hz, and the surface accuracy of the secondary mirror remains relatively unchanged after rapid heat cycles and large-scale vibrations. In the assembling tolerance test, the secondary mirror is only slightly deformed under 0.02 mm unevenness. The proposed rigid support structure can significantly improve the working performance of small- and medium-aperture mirrors and has broad application prospects in the optomechanical structural design of remote sensors. A novel rigid support structure is proposed in this paper to solve the contradiction between thermal stability and structural stiffness in small- and medium-aperture space mirrors assembled using traditional flexible supports. Additionally, a high-precision secondary mirror assembly with a clear aperture of ?214 mm is developed for a high-resolution space camera. The combination of a mirror body, cone, support cylinder, and rigid base plate is adopted to realize heat dissipation by extending and optimizing the transmission path of the thermal stress within the assembly. The secondary mirror assembly with a rigid support structure weighs 2.6 kg, and the surface accuracy change has a root-mean-square (RMS) value of 2.573 nm in the simulation under the condition of a 4 °C uniform temperature rise. The inclination and displacement of the mirror body subjected to the gravity test are 2.028" and 0.566 μm, respectively, revealing the outstanding advantages of the proposed scheme over traditional flexible support systems. The measured surface accuracy RMS value of the secondary mirror is 0.0181λ (λ=632.8 nm), and the changes in the surface accuracy at 16 and 24 °C do not exceed 0.0025λ. The fundamental frequency of the assembly reaches 502.1 Hz, and the surface accuracy of the secondary mirror remains relatively unchanged after rapid heat cycles and large-scale vibrations. In the assembling tolerance test, the secondary mirror is only slightly deformed under 0.02 mm unevenness. The proposed rigid support structure can significantly improve the working performance of small- and medium-aperture mirrors and has broad application prospects in the optomechanical structural design of remote sensors.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0522005 (2024)
Focusing Analysis of Linear Zone Plate with Equal-Width Single-Mode Slits Waveguide Working in Extreme Ultraviolet
Wenxuan Chen, Qing Cao, Changjie Cheng, Chaoyue Li, Jirui Zhu, and Yaxing Mao
With the development of processing technology and the increasing requirement of spatial resolution, the slit widths of linear zone plate have become increasingly small. For slits with different widths on the linear zone plate, the incident uniform plane wave can excite one or more waveguide modes, resulting in inter-mode dispersion and phase differences. Even if there is only single-mode transmission in the slits, the effective refractive index of the fundamental mode is related to the width of the slit, which leads to phase difference of slits with different widths at the exit. To eliminate these phase differences, we propose an equal-width single-mode slit waveguide linear zone plate, study its focusing effect in the extreme ultraviolet band, and establish the corresponding Gaussian far-field analytical model. Numerical simulations based on finite element software confirm the distribution of the Gaussian mode field of fundamental mode, and a calculation based on the Fresnel diffraction integral further confirms the validity of the far-field analytical model. As one example, we design an equal-width single-mode slit waveguide linear zone plate and calculate its normalized one-dimensional light field distribution in the focal plane. With the development of processing technology and the increasing requirement of spatial resolution, the slit widths of linear zone plate have become increasingly small. For slits with different widths on the linear zone plate, the incident uniform plane wave can excite one or more waveguide modes, resulting in inter-mode dispersion and phase differences. Even if there is only single-mode transmission in the slits, the effective refractive index of the fundamental mode is related to the width of the slit, which leads to phase difference of slits with different widths at the exit. To eliminate these phase differences, we propose an equal-width single-mode slit waveguide linear zone plate, study its focusing effect in the extreme ultraviolet band, and establish the corresponding Gaussian far-field analytical model. Numerical simulations based on finite element software confirm the distribution of the Gaussian mode field of fundamental mode, and a calculation based on the Fresnel diffraction integral further confirms the validity of the far-field analytical model. As one example, we design an equal-width single-mode slit waveguide linear zone plate and calculate its normalized one-dimensional light field distribution in the focal plane.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0522004 (2024)
Design of a High-Precision Repeatable Secondary Mirror Deployment Mechanism for Space Cameras
Junwei Song, Xiaoping Tao, Minglin Xu, and Xun Wang
High-resolution imaging in space cameras requires a long focal length, leading to increased distance between the primary and secondary mirrors. Consequently, this results in a larger camera volume and inefficient space utilization. To decrease the launch cost and envelope size of the space camera during launch, a high-precision, repeatable secondary mirror deployment mechanism is designed based on the four-link space structure for the coaxial three-mirror optical system. The mechanism's error was analyzed, and finite element analysis was conducted to evaluate its reliability. Additionally, a repeatability test plan was devised to ensure the mechanism's consistency. Following the folding of the secondary mirror deployment mechanism, the optical axis direction length of the space camera is reduced from 875 mm to 324 mm, achieving a 63% compression in volume. In its unfolded state, the mechanism exhibits a fundamental frequency of 96.64 Hz. The maximum deviation in repeated unfolding displacement is measured at 15.61 μm, and the maximum inclination deviation is 16.89″. These results demonstrate the mechanism's effectiveness in minimizing the space camera's volume and meeting the in-orbit requirements, attributable to its locked state fundamental frequency. Furthermore, the mechanism maintains the optical system's repeatability and can accommodate the payload conditions of micro and nano satellites, making it an ideal solution for aerospace applications. High-resolution imaging in space cameras requires a long focal length, leading to increased distance between the primary and secondary mirrors. Consequently, this results in a larger camera volume and inefficient space utilization. To decrease the launch cost and envelope size of the space camera during launch, a high-precision, repeatable secondary mirror deployment mechanism is designed based on the four-link space structure for the coaxial three-mirror optical system. The mechanism's error was analyzed, and finite element analysis was conducted to evaluate its reliability. Additionally, a repeatability test plan was devised to ensure the mechanism's consistency. Following the folding of the secondary mirror deployment mechanism, the optical axis direction length of the space camera is reduced from 875 mm to 324 mm, achieving a 63% compression in volume. In its unfolded state, the mechanism exhibits a fundamental frequency of 96.64 Hz. The maximum deviation in repeated unfolding displacement is measured at 15.61 μm, and the maximum inclination deviation is 16.89″. These results demonstrate the mechanism's effectiveness in minimizing the space camera's volume and meeting the in-orbit requirements, attributable to its locked state fundamental frequency. Furthermore, the mechanism maintains the optical system's repeatability and can accommodate the payload conditions of micro and nano satellites, making it an ideal solution for aerospace applications.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0522003 (2024)
Design and Analysis of a High Flat Tunable Terahertz Electro-Optical Frequency Comb
Wei Zhang, Feng Zhao, Cong Qiao, Andi Liu, Tegang Yan, Yue Cui, and Mingxing Liu
A high-flat broadband optical frequency comb (OFC) signal generation scheme is proposed, and the mechanism and simulation analysis of the signal generation mechanism and method of high-flat and wideband electro-optical comb are carried out. In the simulation analysis, the dual-drive Mach-Zehnder modulator is used to generate the optical frequency comb signal, the phase modulator is used to further increase the number of comb lines, and finally the flatness is improved by jointly optimizing the drive signal power and DC bias voltage of the Mach-Zehnder modulator. The simulation results show that the scheme can generate a broadband comb signal with a bandwidth of 1.08 THz, with a tone-to-noise ratio of 60 dB and a flatness of 0.5 dB. The proposed scheme is applied to the optical carrier terahertz communication system, and the transmission performance of single-channel and multi-channel 16th-order quadrature amplitude modulation (16QAM) terahertz signals in the case of back-to-back (BTB) or 10 km optical fiber transmission is verified by simulation. The results show that the bit error rate in each of the above cases is lower than the threshold of forward error correction code. A high-flat broadband optical frequency comb (OFC) signal generation scheme is proposed, and the mechanism and simulation analysis of the signal generation mechanism and method of high-flat and wideband electro-optical comb are carried out. In the simulation analysis, the dual-drive Mach-Zehnder modulator is used to generate the optical frequency comb signal, the phase modulator is used to further increase the number of comb lines, and finally the flatness is improved by jointly optimizing the drive signal power and DC bias voltage of the Mach-Zehnder modulator. The simulation results show that the scheme can generate a broadband comb signal with a bandwidth of 1.08 THz, with a tone-to-noise ratio of 60 dB and a flatness of 0.5 dB. The proposed scheme is applied to the optical carrier terahertz communication system, and the transmission performance of single-channel and multi-channel 16th-order quadrature amplitude modulation (16QAM) terahertz signals in the case of back-to-back (BTB) or 10 km optical fiber transmission is verified by simulation. The results show that the bit error rate in each of the above cases is lower than the threshold of forward error correction code.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0522002 (2024)
Bionic Compound Eye Based on a Flexible Fresnel Lens Array
Wenya Zhao, Yecan Zhang, Yonghao Jiao, Haobo Sun, Ningde Miao, Dongdong Han, and Yonglai Zhang
Biological compound eyes have excellent optical properties, including large field of view, small size, no aberrations, and sensitivity to moving objects. Sensitivity to moving objects is crucial for flying insects that chase small, fast-moving targets. Inspired by the sensitivity of compound eyes possessed by insects to moving objects, we prepared a single-layer bionic compound eye with five ommatidia, each consisting of a Fresnel lens. Using femtosecond laser two-photon polymerization processing technology and soft lithography technology, a flexible bionic compound eye with high accuracy and repeatability was prepared. Experimental results show that the prepared bionic compound eye could obtain high-quality images and be used to track moving targets. Biological compound eyes have excellent optical properties, including large field of view, small size, no aberrations, and sensitivity to moving objects. Sensitivity to moving objects is crucial for flying insects that chase small, fast-moving targets. Inspired by the sensitivity of compound eyes possessed by insects to moving objects, we prepared a single-layer bionic compound eye with five ommatidia, each consisting of a Fresnel lens. Using femtosecond laser two-photon polymerization processing technology and soft lithography technology, a flexible bionic compound eye with high accuracy and repeatability was prepared. Experimental results show that the prepared bionic compound eye could obtain high-quality images and be used to track moving targets.
Laser & Optoelectronics Progress
- Publication Date: Mar. 10, 2024
- Vol. 61, Issue 5, 0522001 (2024)
Error Calibration Method of Null Correctors for Large-Aperture Aspherical Mirrors
Qiuyun Xu, and Lingchen Kong
Aspheric mirrors commonly utilize a zero position compensator along with an interferometer for surface shape detection. Therefore, the machining and assembly accuracy of the zero position compensator play a crucial role in determining the reliability of the detection results. This paper introduces a universal compensation error calibration method based on computer generated hologram (CGH). To test the method, a Φ856 mm,f/1.54 hyperboloid mirror is employed as the target aspheric mirror. First, a reflective CGH is designed, and the phase function of the CGH is determined using a ray tracing method. This ensures that the introduced spherical aberration is the same as the normal aberration of the aspheric main mirror to be tested. Subsequently, the correctness of the design is confirmed through ZEMAX simulation calculation, and the primary hologram is processed based on the phase function. Holographic strips are designed and processed on the same glass substrate for adjusting the calibration optical path. The experimental results demonstrate that the CGH calibration achieves a zero position compensator accuracy of λ/80. The proposed method is applicable to concave aspheric mirrors with large apertures and fast focal ratios. Consequently, it can serve as a reliable guide for calibrating zero position compensators in most positive axis aspheric mirrors. Aspheric mirrors commonly utilize a zero position compensator along with an interferometer for surface shape detection. Therefore, the machining and assembly accuracy of the zero position compensator play a crucial role in determining the reliability of the detection results. This paper introduces a universal compensation error calibration method based on computer generated hologram (CGH). To test the method, a Φ856 mm,f/1.54 hyperboloid mirror is employed as the target aspheric mirror. First, a reflective CGH is designed, and the phase function of the CGH is determined using a ray tracing method. This ensures that the introduced spherical aberration is the same as the normal aberration of the aspheric main mirror to be tested. Subsequently, the correctness of the design is confirmed through ZEMAX simulation calculation, and the primary hologram is processed based on the phase function. Holographic strips are designed and processed on the same glass substrate for adjusting the calibration optical path. The experimental results demonstrate that the CGH calibration achieves a zero position compensator accuracy of λ/80. The proposed method is applicable to concave aspheric mirrors with large apertures and fast focal ratios. Consequently, it can serve as a reliable guide for calibrating zero position compensators in most positive axis aspheric mirrors.
Laser & Optoelectronics Progress
- Publication Date: Feb. 25, 2024
- Vol. 61, Issue 4, 0422001 (2024)
Design of a Compact Infrared Continuous Optical Zoom System Based on Alvarez Lenses
Qi Ouyang, Mengyao Liu, Yan Ning, Jie Cao, Qun Hao, and Yang Cheng
In this study, a transverse moving infrared optical continuous zoom system based on the Alvarez lens is proposed to address the challenges associated with the complex structure and large volume of traditional axial-moving mechanical optical zoom systems. The system consists of two sets of Alvarez lenses, apertures, focusing lenses, and infrared detectors. Herein, two sets of Alvarez lenses adopt a Kepler-type telescope structure, where the first set of Alvarez lenses functions as the zoom group and the second set of Alvarez lenses serves as the compensation group. The infinitely far incident light passes through two sets of Alvarez lenses and exits, the emitted parallel light is then focused and imaged onto the target surface of the infrared detector through a fixed focal lens. Utilizing Zemax software for optical simulation, our designed optical zoom system covers the 8?12 μm long wave infrared band, with a maximum field of view angle of 6°, a maximum pupil diameter of 6 mm, an F-number of 2, distortion of <2.1%, and a total optical length of ~74 mm. The Alvarez lens only requires to be horizontally moved by ~1 mm to achieve continuous optical magnification from 5× to 15×. Moreover, the modulation transfer function of the proposed optical zoom system can attain up to 0.5@17 lp/mm, assuming a resolution of 320×240 and pixel sizes of 30 μm for the infrared detector. The simulation results indicate that the system has the advantages of high magnification, a compact structure, and high imaging quality, making it a promising candidate for applications in the field of miniaturized infrared zoom imaging. In this study, a transverse moving infrared optical continuous zoom system based on the Alvarez lens is proposed to address the challenges associated with the complex structure and large volume of traditional axial-moving mechanical optical zoom systems. The system consists of two sets of Alvarez lenses, apertures, focusing lenses, and infrared detectors. Herein, two sets of Alvarez lenses adopt a Kepler-type telescope structure, where the first set of Alvarez lenses functions as the zoom group and the second set of Alvarez lenses serves as the compensation group. The infinitely far incident light passes through two sets of Alvarez lenses and exits, the emitted parallel light is then focused and imaged onto the target surface of the infrared detector through a fixed focal lens. Utilizing Zemax software for optical simulation, our designed optical zoom system covers the 8?12 μm long wave infrared band, with a maximum field of view angle of 6°, a maximum pupil diameter of 6 mm, an F-number of 2, distortion of <2.1%, and a total optical length of ~74 mm. The Alvarez lens only requires to be horizontally moved by ~1 mm to achieve continuous optical magnification from 5× to 15×. Moreover, the modulation transfer function of the proposed optical zoom system can attain up to 0.5@17 lp/mm, assuming a resolution of 320×240 and pixel sizes of 30 μm for the infrared detector. The simulation results indicate that the system has the advantages of high magnification, a compact structure, and high imaging quality, making it a promising candidate for applications in the field of miniaturized infrared zoom imaging.
Laser & Optoelectronics Progress
- Publication Date: May. 25, 2024
- Vol. 61, Issue 10, 1022001 (2024)
Optical System Design of Broadband Hyperspectral Cameras Based on Linear Variable Filter
Yazhen Cui, Chunyu Liu, Yunqiang Xie, and Minglin Xu
Broadband hyperspectral cameras can comprehensively record the spectral information of a target, which is currently a significant research direction in studies on hyperspectral cameras. However, the broadband is bound to cause problems with excessive chromatic aberration and secondary spectra of the system, affecting the image quality. Therefore, based on an analysis method called the Buchdahl vector dispersion model, an optical system of broadband hyperspectral camera based on linear variable filter is proposed in this study. An image side telecentric transmitted optical system with a focal length of 100 mm, F-number of 5, field of view of 14.2°, and spectral range of 400-1000 nm was designed. The hyperspectral camera based on this system can capture images with a spatial resolution of 21.5 m, spectral resolution of 10 nm, and swath width of 125 km at an altitude of 500 km. The image quality evaluation and tolerance analysis show that the system has an excellent image quality and satisfies fabrication and alignment requirements. The modulation transfer function test results show that the system can satisfy actual application requirements. Broadband hyperspectral cameras can comprehensively record the spectral information of a target, which is currently a significant research direction in studies on hyperspectral cameras. However, the broadband is bound to cause problems with excessive chromatic aberration and secondary spectra of the system, affecting the image quality. Therefore, based on an analysis method called the Buchdahl vector dispersion model, an optical system of broadband hyperspectral camera based on linear variable filter is proposed in this study. An image side telecentric transmitted optical system with a focal length of 100 mm, F-number of 5, field of view of 14.2°, and spectral range of 400-1000 nm was designed. The hyperspectral camera based on this system can capture images with a spatial resolution of 21.5 m, spectral resolution of 10 nm, and swath width of 125 km at an altitude of 500 km. The image quality evaluation and tolerance analysis show that the system has an excellent image quality and satisfies fabrication and alignment requirements. The modulation transfer function test results show that the system can satisfy actual application requirements.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2023
- Vol. 60, Issue 9, 0922002 (2023)
Optimal Design of Optical Modules for Double Free-Form Surface Head-Up Display Systems
Xiaowei Chen, Yan Cao, Jialong Xue, Jinwei Ren, Bo Wang, and Shenjiang Wu
To ensure high quality of virtual images in augmented reality head-up display (AR-HUD) systems, the size of the AR-HUD should be reduced as much as possible to achieve a longer distance and a larger field of view. Using an off-axis dual-reflection system with a free-form surface, a virtual image display optical path with a virtual image distance of 10 m and a field of view angle of 10°×5° is designed. Furthermore, the Eyebox (aperture diaphragm offset range) is divided into the moving range of a driver's field of view. The system has nine structures, and multiple structures can be used for the optimization simulation. The light spot from each field of view falls within the Airy disk. The modulation transfer function of the image is close to the diffraction limit, and both the distortion and dynamic aberration values are less than the industry standard values. Once the imaging requirements are satisfied, the dust-proof film of the head-up display (HUD) system is drawn, and the light damage simulation is performed; based on the results, sunlight can be prevented from entering the eyes. Finally, the AR-HUD shell is drawn, and the measured volume is 10 L. The display effect is simulated through a user interface (UI) image to verify the correctness and feasibility of the design. To ensure high quality of virtual images in augmented reality head-up display (AR-HUD) systems, the size of the AR-HUD should be reduced as much as possible to achieve a longer distance and a larger field of view. Using an off-axis dual-reflection system with a free-form surface, a virtual image display optical path with a virtual image distance of 10 m and a field of view angle of 10°×5° is designed. Furthermore, the Eyebox (aperture diaphragm offset range) is divided into the moving range of a driver's field of view. The system has nine structures, and multiple structures can be used for the optimization simulation. The light spot from each field of view falls within the Airy disk. The modulation transfer function of the image is close to the diffraction limit, and both the distortion and dynamic aberration values are less than the industry standard values. Once the imaging requirements are satisfied, the dust-proof film of the head-up display (HUD) system is drawn, and the light damage simulation is performed; based on the results, sunlight can be prevented from entering the eyes. Finally, the AR-HUD shell is drawn, and the measured volume is 10 L. The display effect is simulated through a user interface (UI) image to verify the correctness and feasibility of the design.
Laser & Optoelectronics Progress
- Publication Date: May. 10, 2023
- Vol. 60, Issue 9, 0922001 (2023)
Detection and Lightweight Analysis of Large-Diameter Semi-Annular High-Order Aspheric Surface
Jinlong Cui, Mingyong Hu, Yachao Bi, Zhiwei Feng, Qian Bai, Guangyu Chen, and Jianfeng Xu
This study aims to accurately detect the surface shape of large-aperture high-order aspheric mirrors. A compensation detection system is designed, and lightweight analysis of a semi-annular concave high-order aspheric mirror with inner and outer diameters of 572 mm and 800 mm, respectively, is performed. Based on the theory of three-order aberration, the aspheric mirror is compensated for and detected using the double-lens structure and single-reflecting surface, and a compensation detection system with a root-mean-square (RMS) value of 0.0037λ (λ=632.8 nm) is developed. Triangular holes are used to lighten the high-order aspheric mirror. After achieving light weight, the weight of the lens body becomes less than 30 kg, and the weight reduction rate is 32.7%. A finite element analysis of the high-order aspheric mirror and the support structure under its gravity, combined with the mechanical support structure, is conducted. The RMS values obtained when the optical axis is parallel and perpendicular to the direction of gravity are 0.012λ and 0.013λ, respectively. The maximum stresses on the mirror body and mechanical support structure are 1.308×105 Pa and 1.381×105 Pa, respectively. The stresses on the aspheric mirror and support structure are lower than the ultimate stress of the respective material. This study aims to accurately detect the surface shape of large-aperture high-order aspheric mirrors. A compensation detection system is designed, and lightweight analysis of a semi-annular concave high-order aspheric mirror with inner and outer diameters of 572 mm and 800 mm, respectively, is performed. Based on the theory of three-order aberration, the aspheric mirror is compensated for and detected using the double-lens structure and single-reflecting surface, and a compensation detection system with a root-mean-square (RMS) value of 0.0037λ (λ=632.8 nm) is developed. Triangular holes are used to lighten the high-order aspheric mirror. After achieving light weight, the weight of the lens body becomes less than 30 kg, and the weight reduction rate is 32.7%. A finite element analysis of the high-order aspheric mirror and the support structure under its gravity, combined with the mechanical support structure, is conducted. The RMS values obtained when the optical axis is parallel and perpendicular to the direction of gravity are 0.012λ and 0.013λ, respectively. The maximum stresses on the mirror body and mechanical support structure are 1.308×105 Pa and 1.381×105 Pa, respectively. The stresses on the aspheric mirror and support structure are lower than the ultimate stress of the respective material.
Laser & Optoelectronics Progress
- Publication Date: Apr. 10, 2023
- Vol. 60, Issue 7, 0722003 (2023)
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