Prototype of a linear frequency modulation light source module for FMCW LiDAR

Directly modulated DFB lasers can achieve fast frequency sweeping of output light and serve as the core frequency-modulated light source for FMCW LiDAR. However, inherent frequency modulation nonlinearity exists in directly modulated lasers, which degrades FMCW system performance. This paper proposes a real-time closed-loop nonlinear correction scheme based on FPGA, employing an iterative learning control algorithm. With FPGA as the core correction control unit, a laser driver and nonlinearity correction module prototype integrating a high-precision constant-current source and feedback signal acquisition is implemented. The module realizes automatic nonlinearity correction for directly modulated lasers. At a sweep repetition rate of 5 kHz and a modulation current swing of 100 mA, the nonlinearity decreases from 1.32% and 1.52% to 0.022% and 0.027% before and after correction. Meanwhile, the 1-R² metric is reduced from the 10^-3 order to the 10^-7 order. This work offers an alternative low-cost, high-stability linearly frequency-modulated light source for FMCW LiDAR systems.