Hardware‐Efficient FMCW Laser Ranging Beyond the Coherence Length Approaching the Wiener Phase Noise Limit

Abstract

ABSTRACT Coherent ranging based on frequency‐modulated continuous‐wave (FMCW) lasers is highly promising for autonomous systems. However, the high‐cost laser source hinders the large‐scale deployment of FMCW lidar, which requires both narrow linewidth and large tuning bandwidth. With increasing computational power, digital parameter estimation offers an alternative solution to overcome the laser phase noise, thereby paving the way for low‐cost FMCW lidar. Here, we propose a model‐driven estimation framework that enables high‐precision FMCW ranging beyond the coherence length limit with high hardware efficiency. The optical phase is precisely tracked and recovered without pilots or auxiliary interferometers. Laser ranging beyond the coherence length is realized with a low‐cost 2‐MHz distributed feedback (DFB) laser. A ranging precision of 2.53 cm (1‐ms averaging time) can be achieved at twice the coherence length. The dynamic range is around 63 dB that is 24 dB higher than the conventional method. The length of a 1‐km fiber can be measured with centimeter‐level precision using the low‐cost DFB laser. The precision is only 3 dB higher than the Bayesian Cramér‐Rao lower bound. The method provides a hardware‐efficient solution for low‐cost and high‐precision FMCW lidar, paving the way for large‐scale applications.