Robust Coherent Free-Space Optical Communication Using Ultrashort Pulses and Dynamic Coherent All-Optical Matched Filter

Optical space-ground communication is regarded as the next leap in global connectivity. However, in such free-space optical communication links, atmospheric turbulence causes fluctuations in the intensity and phase of the received light signal, significantly impairing the link budget and rendering the system impractical. This paper presents a novel communication technique designed to mitigate turbulence-induced intensity fluctuations-specifically signal fading and phase distortions-resulting from multipath interference, while still enabling high-order coherent modulation schemes and dual polarization. Spatial distortions can be simultaneously corrected using established adaptive optics techniques. The proposed method is based on transmitting ultra-short pulses, on the order of picoseconds or hundreds of femtoseconds, through a turbulent atmosphere and utilizing a unique detection scheme known as the dynamic coherent all-optical matched filter (DCOF). The system concept, including the atmospheric channel, was evaluated through Monte Carlo simulations. Core photonic engines within this concept were further tested in an experimental laboratory setting, demonstrating the ability to generate and modulate ultra-short pulses, perform coherent detection by mixing two synchronized pulse trains, and optimize detection performance via spectral phase encoding. Both experimental and simulation results indicate the feasibility of a robust coherent free-space optical communication system capable of supporting high-speed data rates.