LiDAR plays a crucial role in vehicle-assisted and autonomous driving by detecting the surrounding environment and aiding in obstacle avoidance. Micro-electro-mechanical system (MEMS)-based LiDARs offer rapid scanning speed, high resolution, and cost-effectiveness, which makes them widely used commercially. A MEMS-based LiDAR with a 360° field of view can comprehensively scan the scene around a vehicle, which offers significant practical value. However, conventional optical systems struggle to achieve consistent outgoing beam divergence angles in both horizontal and vertical directions due to their asymmetric fields of view when attempting 360° scanning. To tackle this challenge, we present a panoramic LiDAR optical system based on MEMS scanning. It enables 360° horizontal scanning of the environment using a torus lens, anamorphic prism, and MEMS mirror. Simulation results demonstrate that our design maintains outgoing beam divergence angles at approximately 0.32° horizontally and 0.13° vertically across different MEMS placement configurations.

The MEMS-based scanning LiDAR system comprises two modules: the transmitting module and the receiving module. The transmitting module includes laser LA, anamorphic prism P1, MEMS, and torus lens L, while the receiving module consists of anamorphic prism P2 and detector D. In the transmitting module, the laser beam emitted by LA undergoes refraction through the special spherical surface S₁ on top of anamorphic prism P1. This beam converges after passing through surface S₁ and then enters MEMS through the lower surface S₂ of anamorphic prism P1. After reflection by MEMS, the beam passes through region A of prism P1 where total internal reflection occurs. The beam then moves into region B where it undergoes refraction before being output. The beam exiting region B is further collimated by toroidal lens L and finally output with a small divergence angle in the horizontal direction. By rotating the MEMS mirror 360° around the Z-axis, the LiDAR achieves a scanning field of view of 360°. The emitted beam strikes an obstacle object, causing diffuse reflection on its surface which scatters light in random directions. Only scattered beams with direction angles closely matching the output beam can enter refraction region B of prism P2. The beams entering region B are redirected towards total reflection region A in prism P2. The reflected beams from region A of prism P2 pass through the bottom surface S₂ of prism P2 and ultimately converge onto detector D. Several crucial considerations must be taken into account for the design of anamorphic prism P1. It is imperative to achieve total internal reflection within region A, which enables ray reflection and manipulation without relying on high anti-reflection film coatings. This necessitates precise control over the angle between the total reflecting surface A and the vertical direction. Another point to note is that surface S₁ of anamorphic prism P1 should have a certain converging effect on the beam, but not collimation. The curvature of surfaces A and B in anamorphic prism P1 differs in the horizontal and vertical directions, which leads to a marked difference in divergence angle between the horizontal and vertical directions as the beam passes through these surfaces. In the design and optimization process, the priority is to ensure good collimation in the horizontal direction. Therefore, a torus lens L is added outside anamorphic prism P1. The torus lens has minimal effect on horizontal divergence but significantly improves vertical collimation. The design concept of anamorphic prism P2 is similar to anamorphic prism P1.

The design of a panoramic LiDAR optical system based on MEMS scanning enables 360° horizontal scanning of the surrounding environment. Moreover, the vertical field of view can be extended up to 6.7°. An anamorphic prism effectively reduces the divergence angle of the output beam to 0.32° horizontally. After passing through the torus lens, it reduces the vertical divergence angle to 0.13°. Simulation results demonstrate that consistent outgoing beam divergence angles of approximately 0.32° horizontally and 0.13° vertically are maintained across different MEMS positions within this system configuration. Transmitting and receiving modules are positioned on either side of the MEMS. Calculation results indicate a maximum detection distance of approximately 200 m. Furthermore, calculations reveal that the ambient light noise reflected by the environment is approximately 0.01 times lower in intensity compared to the useful signal light.

We design a MEMS-based LiDAR system capable of achieving 360° horizontal field of view ring scanning. The system comprises a transmitting module and a receiving module positioned on opposite sides of the MEMS device. The receiving module comprises a specially-shaped prism P2 and a detector D. The top surface of prism P2 is aligned in the same plane as the special-shaped prism P1 of the transmitting module, which maintains a consistent structure throughout. The system achieves high resolution in both horizontal (0.32°) and vertical (0.13°) directions, utilizing minimal components and featuring a compact structure. Moreover, the optical components are symmetrically oriented, which results in manageable processing complexity and immense commercial potential for this system. Future research will focus on analyzing the influence of manufacturing tolerances and equipment variations on resolution.