The influence of circularly polarized light on FMCW LiDAR signal persistence in fog environments

Due to advances in sensor technology which enable reliable navigation and collision avoidance, there is a marked increase in the use of autonomous transportation. Light detection and ranging (LiDAR) sensors are employed in this context because they function over useful ranges for transportation applications and can provide high resolution imaging and ranging. However, receiving accurate sensor feedback through degraded visual environments (DVE’s), like smoke and fog, remains a significant challenge. Conventional LiDAR uses linearly polarized light which does not maintain its polarization well in high-scatter environments. Research has shown that circularly polarized light has improved persistence in fog environments (i.e., it maintains polarization) which makes transmitted signals more discernable through DVE’s. Here, we investigate how circularly polarized light impacts frequency-modulated continuous-wave (FMCW) LiDAR performance in fog. FMCW LiDAR is of particular interest because it uses coherent detection to amplify the signal of interest, boosting signal-to-noise ratio. We also investigate the persistence of circular polarization for a range of targets that can be found in everyday circumstances to assess which types of targets can be sensed by a circularly polarized LiDAR system. For our experiments we use our tabletop aerosol chamber to generate an analogue of a real-world fog that recreates degraded transportation conditions. We transmit both linearly and circularly polarized signals and measure their polarization extinction ratio upon return through fog from a gold mirror. Our results demonstrate that using circularly polarized light in FMCW LiDAR improves polarization persistence in fog and merits further investigation into all-weather LiDAR systems.