Design and Control of a frequency linear modulation system for FMCW LiDAR

Abstract

LiDAR (light detection and ranging) is used in a variety of fields such as robotics, autonomous vehicles, and military due to the advantage of being able to measure distance with or without external lighting. A pulsed ToF (time of flight) LiDAR, which is widely used in related fields, is sensitive to environmental factors such as fog, rain, and strong sunlight. However, FMCW (frequency modulated continuous wave) LiDAR is robust to environmental factors. It can also measure the velocity and distance of an object at the same time. In FMCW LiDAR, frequency linear modulation is important to improve its measurement performance such as distance measurement accuracy and SNR(signal to noise ratio). However, due to the characteristic of tunable lasers, the laser frequency is not modulated linearly even when the input is linear. Therefore, various methods such as feedback control and feedforward control for frequency linear modulation is being studied. However, the conventional feedback control is not suitable for LiDAR systems requiring a high measurement repetition rate because of loop delay, and the conventional feedforward control has the limitation that it cannot be applied when the laser is changed or the laser characteristics are changed due to temperature change. In this paper, a method is proposed to overcome the limitations of conventional control methods. The frequency linear modulation system is designed and controlled according to the proposed method and verified through experiments.