Visible-IR transmission enhancement through fog using circularly polarized light.

Detection range is an important factor affecting the transmission characteristics of polarized light through fog. We first selected certain spectral bands from visible to IR wavelengths that exhibit lower path loss. For both radiation fog and advection fog, these optimized wavelength ranges include 0.4-1.1 μm, 1.48-1.56 μm, 1.63-1.86 μm, 2.03-2.18 μm, and 2.39-2.45 μm, and radiation fog in particular contains 3.5-4.3 μm. The long-wave IR wavelengths were excluded due to higher absorption losses. We further investigated the transmission performance of circular and linear polarization in variable foggy environments, exploring the impact of the detection range in particular. Using polarization-tracking Monte Carlo simulations for varying particle size, wavelength, refractive index, and detection range, we show that circular polarization outperforms linear polarization when transmitting in both radiation and advection fog. For radiation fog, circular polarization persists longer than linear polarization for 5 μm and 9 μm particles over the entire optimized wavelength range from the visible to mid-wave IR (MWIR). However, linear polarization outperforms circular polarization for 1 μm particles over the entire MWIR and a part of the short-wave IR (SWIR). For advection fog, circular polarization persists longer than linear polarization for all three particle sizes (10, 20, and 40 μm) over the entire optimized wavelength range from the visible to SWIR. We show that circular polarization retains a higher degree of polarization and has better enhancement in some detection ranges.