This is our third installment of a four-series blogs about steering mirrors. We have talked previously aboutsteering mirrors in laser markingsandsteering mirrors in OCTsystems. This week, we will talk about the steering mirror requirements for those in LIDAR systems. In the past we, have talked about thelens design in LIDARsystem, as well ashow to make LIDAR systems cheaper.
光检测和范围（LIDAR）是为自动驾驶汽车中广泛使用的数十种机器人应用的必不可少的技术。LIDAR用于测量与物体的距离。这是通过从源中发送激光脉冲来完成的，然后将其反射为对象。检测到反射的光，并根据光子返回时间计算出飞行时间（TOF）的估计。
激光束转向是LiDAR系统中的重要组成部分。机械扫描系统是使用万山坐骑，快速的镜子，里斯利棱镜，旋转的多边形镜子和光栅设计的。通常，我们希望拥有几乎没有运动部件或没有运动部件的转向机制，而小的惯性则用于快速和紧凑的梁转向设备，以便可以降低大小，重量，成本和功耗。这些要求对于自动驾驶车辆尤为重要。虽然可以设计非机械扫描系统，例如空间光调节器，光学阶段阵列和液晶电流扫描仪，但它们尚不非常常见。
在自动驾驶汽车的激光雷达应用中，需要一个较大的转向角（约40度）以及较大的光束尺寸，以覆盖大角度的扫描角度并最大程度地减少由于衍射而导致的光束差异。图1显示了LIDAR光学系统扫描镜头以及F-Theta lens.
Figure 1. LIDAR Optical System. Image from Xiaobao Lee and Chunhui Wang, Appl. Opt. 54, 2219-2223 (2015)
In recent years, a popular solution for creating the LIDAR steering mirror is using MEMS technology. Although MEMS micromirrors can usually just tilt around 10-degrees, it is possible to increase the system FOV by combining the MEMS with additional optical components. Even a simple telescope-type structure is capable of increasing the FOV angle by a factor of 5. Depending on your application, the latter may ne be desired as it will affect the beam distribution.
In general, if you are detecting fast-moving objects at a large distance (like in a case of an self-driving vehicle), you will need to correct the beam distribution. If you are interested in mapping relative static areas, it may not be so critical.
A scanning electron microscope of a MEMS mirror used in LIDARs is shown in Figure 2.
Figure 2. Scanning electron microscope image of a MEMS mirror. IMAGE: IEEE Spectrum DINGKANG WANG
