Designing high power, low linewidth, PIC based external cavity lasers with extended FMCW chirp

Abstract

In recent years, significant improvements in the output power of DFB laser chips have been achieved, which benefits automotive solid-state FMCW LiDAR systems. However, these high-power devices generally produce significant noise, increasing their linewidth. External cavity diode lasers (ECDL) offer a pathway to high power and low linewidths, especially when high-Q resonators are used inside the cavity. LiDAR system performance requires design of a laser with a mode-hop free (MHF) chirp excursion of >3GHz, a chirp rate of 10-100kHz and an optical output power of >500mW with a deviation of <1dB. Generally, in PIC technology, heaters are used to tune the resonant frequencies with speeds upto <10kHz. So, to achieve higher chirp rates, the gain section is directly modulated via current injection. Due to the narrow resonance of the high-Q resonator in a PIC based ECDL, the MHF chirp is very limited, <1GHz, the output power will fluctuate in the order of 3-6dB over the entire MHF chirp range. Here, we present a specific design tailored to achieve MHF tuning ranges of ~10GHz, with stable output power and chirp rates of ~100kHz, laser linewidth <10 kHz and output powers >500mW.