激光雷达 (Light Detection And Ranging, LIDAR) 是以激光为载体，用来探测目标位置等特征量的雷达系统。由于激光具有抗干扰能力强、测量范围广、可靠性好的特点，在三维成像领域激光雷达可以适应更为复杂的环境，实现图片更高的清晰度和分辨率。在目前室内场景重建、无人驾驶、机器人等领域有极为广泛的应用前景。小型化、低成本和高精度一直是未来成像激光雷达的发展方向。为此，本文从成像激光雷达原理入手，对雷达系统进行了整体设计，并对其中器件选型、光学系统设计和二维扫描等关键技术进行了研究与讨论，初步搭建了激光雷达系统并通过实验进行验证。本文从以下几个方面展开:首先，介绍了成像激光雷达在国内外研究现状，根据国内已取得的非扫描与扫描式成像机制成就，确定了本文利用二维微机电系统 (Micro-Electro-Mechanical System, MEMS) 振镜扫描的成像方式。其次，介绍了成像激光雷达设计的基本原理。包括雷达探测机制、大气对激 光传输的影响、激光雷达距离方程以及光电转换模块的原理。基于本文设计要求，选择了直接探测的方式以及以雪崩光电二极管 (Avalanche Photo Diode, APD) 为核心的光电转换模块。然后基于成像激光雷达原理确定了系统整体设计方案，主要包括发射、扫描、接收和信号处理四部分。根据系统目标，计算得到了激光器的相关参数要求。接着重点介绍了MEMS 的逐行扫描和李萨如扫描两种二维扫描技术，并对振镜的扫 描角度以及扫描轨迹进行了测试实验。本文还从多个角度比较了收发合置与收发分置光学系统的优劣，详细介绍了设计的以偏振分光棱镜 (Polarizing Beam Splitter, PBS) 为光学隔离开关的收发合置光学系统结构，并且就如何提高系统信噪比展开研究，另外与现有的收发合置系统相比，创新性地将系统杂散光作为距离探测的起始光信号，解决了杂散光影响探测的固有问题。理论上分析了系统发射与接收性能，并通过实验进行了验证。最后介绍了以现场可编程门阵列 (Field Programmable Gate Array, FPGA) 为核心的信号处理系统。利用FPGA实现了延迟线插入法测量时间间隔，并进行了近距离激光测距实验，测量误差达到厘米量级。
Light Detection And Ranging (LIDAR) is a radar system that uses laser as a carrier to detect feature quantities such as the target position. Because the laser has strong anti- interference ability, wide measurement range and good reliability, the LIDAR can adapt to more complex environments in the field of three-dimensional imaging, achieving higher definition and resolution of the picture. And it has a wide range of application prospects in the fields of indoor scene reconstruction, autonomous driving, ground robots.Miniaturization, low cost and high precision have always been the development direction of future imaging LIDAR. To this end, this paper starts with the principle of imaging LIDAR, and designs the radar system as a whole. The key technologies such as device selection, optical system design and two-dimensional scanning are studied and discussed. This paper initially built a laser radar system and verified it through experiments. This paper starts from the following aspects:Firstly, the research status of imaging laser radar at home and abroad is introduced. According to the achievements of non-scanning and scanning imaging mechanisms obtained in China, this paper determines to use two-dimensional micro-electro-mechanical system (MEMS) galvanometer scanning.Secondly, the basic principle of imaging LIDAR design is introduced, which includes radar detection mechanisms, the effects of the atmosphere on laser transmission, the LIDAR distance equation, and the principles of photoelectric conversion modules. Based on the design requirements of this paper, the direct detection method and the photoelectric conversion module with Avalanche Photo Diode (APD) as the core are selected.Then based on the principle of imaging LIDAR, the overall design scheme of the system is determined, which mainly includes four parts: transmission, scanning, receiving and signal processing. According to the system goal, the relevant parameters of the laser are calculated. Then, the two-dimensional scanning technology of MEMS progressive scanning and Lissajous scanning is introduced, and the scanning angle and scanning trajectory of the galvanometer are tested.This paper also compares the advantages and disadvantages of division and mono- static optical systems from several angles, and introduces the structure of monostatic optical system with polarized beam splitter (PBS) as optical isolation switch. This paper studies how to improve the system signal-to-noise ratio. In addition, compared with the existing monostatic system, the system uses the stray light as the starting light signal for distance detection, which solves the inherent problem of stray light impacting detection. The transmitting and receiving performance of our system is theoretically analyzed and verified by experiments.Finally, the signal processing system based on Field Programmable Gate Array (FPGA) is introduced. The time interval of the delay line insertion method was mea- sured by FPGA, and the close-range laser ranging experiment was carried out, and the measurement error reached the order of centimeter.
