| 紧凑低成本非制冷长波红外连续变焦光学设计 |
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| 引用本文： | 唐晗,郑万祥,曾兴容,杨丹,周春芬,曹凌,徐曼,李洪兵,杨开宇.紧凑低成本非制冷长波红外连续变焦光学设计[J].红外与激光工程,2023,52(4):20220607-1-20220607-11. |
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| 作者姓名： | 唐晗 郑万祥 曾兴容 杨丹 周春芬 曹凌 徐曼 李洪兵 杨开宇 |
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| 作者单位： | 昆明物理研究所，云南 昆明 650223 |
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| 基金项目： | 国家重点研发计划(0701200) |
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| 摘 要： | 随着红外技术的快速发展，SWaP-C (尺寸小、质量轻、功耗低、成本低)概念已深入红外热像仪整机设计全过程。在非制冷连续变焦红外热像仪设计中，相对已模块化的非制冷探测器与成像电路、光学系统影响整机包络尺寸、产品质量及价格成本，因此设计一款总长短、质量轻、成本低、性能高的非制冷长波红外连续变焦光学系统将具有广阔的市场前景。非制冷长波红外连续变焦光学因相对孔径大、光学材料种类少等因素存在系统小型化和无热化设计难题，通过采用变F#设计方法约束物镜尺寸；利用三组联动变焦技术平衡像差、压缩系统总长；通过主动补偿的消热差技术使得系统在-40～+60℃温度范围成像质量良好，实现四片透镜构成的非制冷长波红外连续变焦光学系统设计。该系统工作波段为8～12μm，焦距变化范围为20.7～126 mm，对应F#为1.05～1.2，视场变化范围为21°×16.8°～3.5°×2.8°，变倍比为6.0×，最大物镜直径116 mm，光学系统总长180 mm，光学零件总质量418 g。该光学系统具有轻小型、高性能、低成本等SWaP-C特征，将在无人装备平台及手持热像仪设备中得到广泛应用。
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| 关 键 词： | 非制冷长波红外 连续变焦光学系统 变F#设计 三组联动变焦 无热化 |
| 收稿时间： | 2022-08-25 |
Compact and low-cost uncooled LWIR continuous zoom optical design |
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| Affiliation: | Kunming Institute of Physics, Kunming 650223, China |
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| Abstract: | Objective With the rapid development of infrared technology, the concept of SWaP-C (small size, light weight, low power consumption and low cost) has been expanded from infrared detector to the whole design process of infrared thermal imager. In the design of uncooled continuous zoom infrared thermal imager, compared with the modularized uncooled detector and imaging circuit, the optical system affects its envelope size, product weight and price cost. A light, small, low-cost, high-performance uncooled infrared optical system needs to achieve the following five goals. First, the number of lenses is as small as possible. Second, the length of the optical system is short. Third, the diameter of the large objective lens is small. Fourth, the optical system has high MTF. Fifth, the optical system has good environment adaptability. Therefore, the design of an uncooled LWIR continuous zoom optical system with short length, light weight, low cost and high performance will have broad market prospects. Methods There are difficulties in miniaturization and athermalization design of uncooled LWIR continuous zoom optical system due to its large relative aperture and few kinds of infrared optical materials. The purpose of compressing the total length of system and balancing aberration is achieved by using three groups of linkage zoom technology. Through the active compensation of athermalization technology, the system has good imaging quality in the temperature range of ?40-60 ℃. The specific design process of the optical system is as follows. Firstly, the calculation program is compiled according to the three groups of linkage continuous zoom models. According to the design index, the initial optical form is calculated by considering the total optical length, lens focal length distribution and lens spacing. The parameters are input into Zemax optical design software to establish the ideal optical model. Secondly, the shape and material are reasonably selected according to the focal length of the lens, and the evaluation function is set to enter the optimization and global optimization. Thirdly, according to the results of the evaluation function, the imaging quality at normal temperature and at high and low temperature is evaluated. Then, the tolerance analysis of optical system is carried out to make the system meet the tolerance range of processing and assembly requirements. Finally, the optical system zoom curve renormalization operation is carried out to complete the optical system design. The design flow chart is shown (Fig.2). Results and Discussions The final design result of the compact and low-cost uncooled LWIR continuous zoom optical system is shown (Fig.4). The whole system uses four lenses with the working band of 8-12 μm, the focal length range of 20.7-126 mm, the corresponding F# of 1.05-1.2, the field of view range of 21°×16.8°-3.5°×2.8°. The zoom ratio is 6.0×, the maximum machining diameter is 116 mm, the total length of the optical system is 180 mm, the total weight of the optical part is 418 g, and the telephoto ratio is 1.44. The MTF, SPT and distortion of the optical system are analyzed by Zemax optical simulation software. The system imaging is clear and meets the requirements. The MTF of the optical system at normal temperature (Fig.5), the SPT of the optical system (Fig.6). and the system distortion (Fig.7) are shown. The imaging quality of the optical system is evaluated at high and low temperature, and the optical system meets the requirements of athermalization. The tolerance of the optical system is estimated by statistical algorithm, and the tolerance of the system meets the actual use requirements. By renormalizing the cam curve of the optical system, the motion curves of the three lenses are obtained (Fig.15). The optical system achieves the SWaP-C goals. Conclusions Based on a 640×512 uncooled focal plane detector with pixels size of 12 μm, a compact low-cost continuous zoom optical system composed of four lenses was designed using variable F# design method, three groups of linkage zoom design technology and active compensation for athermalization. The focal length of the system varies from 20.7 mm to 126 mm, the total optical length is 180 mm, the lens processing technology is mature, the processing and adjustment tolerance is good, the zoom cam curve is smooth, the cam track is easy to process, and the motion servo control is simple. The system has clear imaging in the environment of ?40 ℃ to +60 ℃. The optical system has the characteristics of light weight, high performance and low cost. It will be widely used in unmanned equipment platform and handheld thermal imager equipment, and promote the development of uncooled infrared thermal imager in the direction of reducing SWaP-C. |
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