A 4-D FMCW LiDAR with Ultra-High Velocity Sensitivity

This work presents a novel scheme for a 4-dimensional (D) frequency modulated continuous wave (FMCW) LiDAR, which demonstrates an unprecedentedly high velocity sensitivity. This is achieved by utilizing the driving waveform to minimize the phase noise originating from the distributed feedback (DFB) laser during the wavelength sweeping process on the transmitting side, while on the receiving end, we use a combination of a self-injection-locked oscillator (SILO) and an avalanche photodiode (APD) with a cascaded multiplication layer, to ensure excellent responsivity and saturation current performance. Comparison is made with a reference LiDAR system comprised of the traditional radio-frequency (RF) oscillator with a p-i-n PD at the receiving-end. The results show that our SILO + APD design provides much better quality 4-D images of slow-moving objects (5 μm/sec) and state-of-the-art velocity sensitivity. This can be attributed to a reduction in the phase noise of the down-converted baseband signals, which is beneficial to the resolution of a small Doppler frequency shift. Furthermore, the incorporation of a high-performance APD also improves the contrast ratio between the object and the background pixels. These improvements offer new possibilities for the development of the next generation of 4-D FMCW LiDARs capable of simultaneously providing the absolute 3-D geometric size and small vibration information.