Simplified Eye-Safe Pulsed ToF LiDAR With Modified Newtonian Telescope for Long-Distance High-Resolution Detection in Rain Atmosphere

We demonstrate a 1.5- $\mu $ m pulsed time-of-flight (ToF) LiDAR with 1-km detection distance and 1.7-cm ranging resolution in heavy rain atmosphere with a visibility of 1 km. The signal processing scheme is simplified by denoting leakage signal of an optical circulator in the sending and receiving unit as the reference signal. Hence, the combination of reference and echo signals into one signal detection and processing channel can be realized for a low-cost and compact system design. Moreover, modified Newtonian telescope, characterized with high echo signal harvesting efficiency and nearly no detection energy waste, is first proposed by transforming the Gaussian detection laser into a ring-shape laser with an axicon-based relay optics, where the intensity of the detection signal (~0.57 W/cm2) can be controlled to meet the human eye safety standard. Finally, the LiDAR performance is verified under regular and rainy atmospheres, and a BOXCAR algorithm is applied to deal with the weak echo signal in tough weathers. The results pave a way for further development of the current system in wild environments for disaster prevention.