Objective In the one-to-many laser communication indoor principle verification system, the antenna adopts multi-faceted tilt-mirror with independent optical axis alignment function to realize one point and multi-point laser communication in a broad range. To reduce the size and working envelope of the tilt-mirror in the laser communication ground test system to meet the limitation for size, a compact and integrated tilt-mirror with SiC/Al is proposed in this paper. The tilt-mirror can be connected to the turntable’s pitch axis seat to reduce the reflecting surface’s eccentric distance and the whole machine’s outer envelope size. The tilt-mirror and supporting structure’s mounting surface can only be separately grinded and then installed since the structure restrict the system. The test shows that when the grinding accuracy is 5μm, the tilt-mirror profile accuracy cannot meet the design requirements. The mounting surface must also be repaired by grinding several times according to the surface inspection results after the tilt-mirror is installed. However, the system has three independent tilt-mirrors, which makes the repair grinding cycle long and complicated. Thus, the tilt-mirror must be optimized to consider the impact of grinding errors on the surface quality and reduce the requirements for the surface quality of the mounting surface. This study focuses on the tracking tilt-mirror structure in the networked laser communication ground demonstration prototype, which causes the reflector and mounting base unable to use the traditional bonding process and can only be installed with screws, resulting in serious degradation of the reflector surface during the screw connection process. Theoretical and simulation analyses are conducted to verify the reasons and laws of the problem based on the original structure’s test results. It then optimized the design to improve the mirror surface’s stability, ensuring that the design requirements are met.
Methods First, the initial design mirror’s surface shape changes under different mounting points are tested. The theoretical calculations are conducted based on the experimental and test results of the original reflector structure. The analysis proves that the unevenness of the structure’s installation points affects the mirror surface’s accuracy. The law is consistent with the test results. Next, through finite element analysis, the influence of each installation point of the original structure is simulated, and compared with the test result, the reason and law of the problem are verified. It is obtained that the conventional grinding and other mechanical methods cannot meet the requirements. Thus, the tilt-mirror needs to be optimized and improved. The flexible structure is then used to isolate the stress transmission, and the tilt-mirror is optimized based on the original design. The flexible structure with isolation trenches is used to solve the problem of surface degradation. Therefore, isolation grooves are designed on the mounting plate to reduce the mounting surface’s flexibility and effectively isolate the installation force’s transmission. The analysis showed that the surface deformation of the high-quality surface tilt-mirror reduced significantly. Also, the surface stability of the tilt-mirror has significantly been improved. The ability to suppress the external forces influence is greatly enhanced, ensuring that the tilt-mirror meets the design index requirements after installation. Finally, it verified the mirror surface’s accuracy through static surface testing and verified its practical application effect through dynamic spot detection.
Results and Discussion The surface quality test shows that the tilt-mirror surface shape’s peak-valley value is better than λ/6, and the root-mean-square value is better than the λ/52 (Fig. 7 and Table 2). It shows that the integrated tilt-mirror with high surface stability guarantees its surface stability under the influence of installation flatness and temperature load and fully meets the design requirements. In multi-laser communication antennas using the high-surface stability integrated tilt-mirror mirrors and indoor demonstration experiments, the camera’s image processing software is used to identify the light spot in the fine tracking camera when capturing static (pointing but no tracking) and dynamic (dynamic tracking), and extract the light spot’s pixel information in the x- and y-axes directions (Fig. 9). Comparing the changes in spot size in different states and at different times, it can be seen that the spot roundness is better, and the spot roundness is slightly reduced under dynamic conditions, but the effect is small (Table 3).
Conclusion Aiming at the problems that the structure limits the compact tilt-mirror in the networked laser communication system, the grinding accuracy of the mounting surface affects the surface accuracy of the reflecting surface, and the surface accuracy after installation is remarkably reduced and cannot meet the design requirements, the stability of the tilt-mirror surface is optimized through theoretical analysis and finite element simulation. The mechanical characteristics of the integrated tilt-mirror installation are analyzed and investigated. The influence of the installation point parameters on the surface of the tilt-mirror is analyzed. The installation point position of the integrated tilt-mirror is optimized, and the parameters of the integrated tilt-mirror are designed. Because of the particularity of the tilt-mirror processing and installation methods, the flatness’ influence law and strength are analyzed. The isolation structure is designed to suppress the flatness’ influence, ensuring the integrated tilt-mirror’s surface stability after installation. The surface accuracy test results show that the tilt-mirror fully meets the design requirements after installation.
