The basic principle of three-dimensional (3D) imaging lidar-an active imaging technology, is parallel laser ranging. Compared with traditional passive sensor imaging and microwave radar, the 3D imaging lidar has obvious advantages, so it promises to possess a wide application prospect. Non-scanning 3D imaging lidar has seven modulation modes. Among them, the 3D imaging lidar based on polarization modulation has the advantages of large measurement range, high measurement accuracy, fast imaging speed, and no motion artifacts. At the same time, it is not limited by other modulation methods, such as intensified charge coupled device and avalanche photodiode array detectors, and its process is complex but easy to saturate and damage. However, its disadvantage is that it requires two cameras, electro-optic crystal limits the imaging field of view, and is easily affected by atmospheric conditions such as incident angle and cloud and mist.
In order to overcome the above shortcomings, in this paper we propose to use polarization imaging lidar and short-wave infrared zoom optical system to construct a dual-mode target detection imaging system by means of common aperture, which can not only reduce the volume of the two systems and solve the coaxial problem of the two systems, but also solve the problems such as the influence of atmospheric conditions (small viewing angle, incident angle and cloud and mist) on imaging quality of polarization modulation imaging lidar and the limitation of low energy of short-wave infrared imaging targets. According to the above ideas, the design and research of polarization imaging lidar and shortwave infrared composite optical system are carried out. The optical design software is used to complete the optical design of the telescope group, shortwave infrared imaging lens group, polarization modulation lens group and the system as a whole. In the telescope group the off-axis three-mirror structure is used to solve the blocking problem of the center of the field of view, and in the shortwave infrared lens group the type of mobile zoom compensation group is used to realize zooming. Analysis of the image quality of the optical system shows that the designed optical system has high imaging quality and its optical design meets the requirements for system design. The optical simulation software is used to simulate the imaging process of the optical system. The results show below. The polarization imaging lidar and shortwave infrared imaging have high quality, the stray light has little influence on the imaging of the system, the target edge imaging is clear, and the independent square targets with a 1-m in diameter can be distinguished. The field of view of the short-wave infrared short-focus mode is 9 times that of the long-focus mode. The shortwave infrared telescopic mode is basically consistent with the field of view of polarization imaging lidar. The received illuminance value of polarization imaging lidar is about 2.4 times that of short-wave infrared long focal length mode. The overall energy distribution of polarization imaging lidar is more balanced, and the imaging effect is better. The method adopted in this paper provides a new idea for studying the polarization modulated imaging lidar. The next step in experimental research is to complete the physical processing, assembly and adjustment, and selection of suitable targets.
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