FMCW LiDAR with a GaN-based distributed feedback laser diode at 466 nm

Frequency-modulated continuous-wave (FMCW) LiDAR requires a visible narrow-linewidth laser capable of a wide linear chirp for operations in underwater environments. To this end, we evaluated a GaN-based 466 nm distributed feedback laser diode (DFB-LD) using a delayed self-heterodyne interferometer, measuring its modulation waveform. The chirp span reached a 12.2 GHz peak-to-peak value (Fourier-limited theoretical resolution: 0.92 cm in the water). The modulation nonlinearity was 9% full scale, and the coherence length was 14 m (β-separation linewidth: 1.9 MHz). Using the proposed LD, we demonstrated free-space FMCW LiDAR at ∼3 m without predistortion. Although the resolution degraded to ∼2 m due to nonlinearity and frequency noise, this work represents, to our knowledge, the first experimental demonstration of FMCW LiDAR using a visible DFB-LD, showing its potential for visible coherent sensing.