Improving chirp and ranging of FMCW LiDAR by external cavity laser design

Abstract

Recent advancements in Distributed Feedback (DFB) lasers have improved output power levels, offering benefits for automotive FMCW LiDAR. However, these high-power DFB lasers often show increased phase noise and broader linewidths. External Cavity Diode Lasers (ECDLs) offer an alternative, enabling high output power with narrow linewidths—especially when incorporating high-Q resonators within the external cavity. For optimal LiDAR performance, the laser must support a mode-hop-free (MHF) chirp excursion > 3 GHz, chirp rates on the order of several hundred kHz, and maintain optical output power above 500 mW with less than 1 dB variation. In photonic integrated circuit (PIC) implementations, linewidths as low as 1 kHz are achievable using high-Q resonators. However, the narrowband nature of these resonators limit the MHF tuning range to < 1 GHz and results in significant power fluctuations (3–6 dB) across the chirp range. This work presents a laser design targeting an MHF tuning range of approximately 10 GHz, with stable output power, chirp rates around 100 kHz, a linewidth below 10 kHz, and output power exceeding 500 mW—making it suitable for next-generation FMCW LiDAR in automotive applications.