# Research on Optical System of Dim Target Simulator Based on Polarization Stray Light Suppression
## 1 Introduction  
Since Sputnik 1, with the development of deep space exploration technology, nearly 90,000 man-made space targets can be detected, and human exploration of space is also developing towards smaller and darker targets [1]. Therefore, effectively reducing the false alarm rate of optical detectors and realizing high-precision detection of smaller dim targets have become urgent problems in the field of space detection. However, due to the limited resources and high cost of the on-orbit platform [2], laboratory physical simulation of the optical characteristics of dim space targets has gradually developed into one of the important guarantees for the successful completion of the deep space exploration mission of optical detectors. The field of dim target simulation mainly serves the ground calibration and correction of dim target observation equipment, so the important factor in this field is how to more accurately simulate the optical characteristics of the target observed by the observation equipment. Airbus DS's Star Tracker Optical Simulator (STOS) [3], for the first time as the star chart display devices using LCOS, realize the dynamic display of the star chart, and star position simulation error is superior to 20\({}^{\prime\prime}\). Subsequently, Germany Jenaoptronik alsolaunched an Optical Star Simulator (OSI) [4] and improved the star position correction algorithm; the star position simulation error is better than 18\({}^{\prime\prime}\), and the magnitude simulation range is +2\(\rightarrow\)+8 Mv. With the development of dynamic display technology, the US Air Force Research Laboratory developed TASAT [5], which is used for the high-precision simulation of the photoelectric tracking process of the photoelectric detection system on the satellite and other targets. The STK EOIR module [6] developed by AGI is used for the simulation of various photoelectric payload imaging processes. Harbin Institute of Technology [7] proposed a digital image generation method for starry background statistics in an all-sky area, which used the imaging signal intensity model, the statistical function of the number and magnitude of stars, and the imaging characteristics of stars on the focal plane to generate starry background images above +10 magnitude stars. Although some progress has been made in the field of image simulation for space-based applications, this method is only validated for observation algorithms, and optical imaging methods for simulation images are still lacking for performance evaluation of space-based observation equipment. Changchun University of Science and Technology [8] applied the LCOS splicing display technology to the development of a dynamic star simulator; the star position simulation error was better than 25\({}^{\prime\prime}\), and the magnitude simulation error was better than \(\pm\)0.5 Mv. In the subsequent research, the team developed a high-contrast LCOS splicing dynamic star simulator using multiple superimposed prisms to solve the influence of polarization degree on the stray light [9]. The star position simulation error is less than 18\({}^{\prime\prime}\). In view of the problem of stray light in optical engines, [PERSON] [10], [PERSON] [11], and other teams have also carried out relevant research, but the redesigned optical engine has problems such as increased volume and reduced energy utilization, and it is difficult to apply to the high-precision simulation of dim targets. In summary, the dynamic dim target simulation technology has some problems, such as the difficulty of avoiding stray light in the dynamic display scheme, the increase in system volume caused by the method of eliminating stray light, and the difficulty of improving the simulation accuracy of dim targets. Therefore, an optical simulation method for dim targets based on polarization stray light suppression is proposed in this paper.