Single-shot ranging and velocimetry with a CW lidar far beyond the coherence length of the CW laser

Abstract

The spectral linewidth of the continuous-wave (CW) lasers is one of the key limitations on the coherent lidar systems, which defines the maximum detection range. Furthermore, precise phase or frequency sweeping requirements are a deterrent in many applications. Here, we present the Phase-Based Multi-Tone Continuous Wave (PB-MTCW) lidar measurement technique that eliminates the necessity of using high coherence laser sources as well as any form of phase or frequency sweeping while employing coherent detection. In particular, we modulate a CW laser source with multiple radio-frequency (RF) tones to generate optical sidebands. Then, we utilize the relative phase variations between the sidebands that are free from laser phase noise to calculate the target distance via post-processing and triangulation algorithms. We prove that the PB-MTCW technique is capable of performing single-shot ranging and velocimetry measurements at more than 500× the coherence length of a CW laser in a benchtop experimental demonstration. Overall, precise phase or frequency sweeping requirements and the spectral linewidth of CW lasers, which defines the maximum detection range, are the key limitations of long-distance coherent lidar systems. The proposed approach overcomes these limitations and enables single-shot ranging and velocimetry measurements, especially for long-range applications such as spacecraft and airborne coherent lidars.