Simulation of Fog-Induced Attenuation and Inter-Symbol Interference in Mid-and Long-Infrared Free-Space Optical Communications

<div> Free-space optical (FSO) communications offer large bandwidths but are strongly affected by atmospheric fog. Recent advances in quantum cascade lasers enable high-speed transmission in the mid-and long-infrared ranges (3-6 and 8-12 µm), which are expected to provide increased robustness compared to the conventional visible or 1.55 µm bands. In this work, light propagation through fog is modeled using a time-domain approximate radiative transfer equation solver, accounting for wavelength-dependent scattering, absorption, and droplet size distributions of a realistic fog scenario, demonstrating its advantages against visibility-based models for satisfactory evaluation of FSO links performance in the mid-and long-infrared. The model is applied to an example optical communication link to assess attenuation and inter-symbol interference effects. Quantitative results indicate that long-infrared wavelengths exhibit reduced temporal spreading and improved tolerance to fog-induced impairments. </div>