Interaction Between Adaptive Optics and Mode Diversity Reception in GEO Optical Downlinks

Atmospheric turbulence significantly hinders the reliability of satellite-to-ground laser communication, posing a particularly severe challenge for Geostationary Earth Orbit (GEO) links. Adaptive optics (AO) combined with mode diversity reception (MDR) is an effective turbulence mitigation strategy (referred to as AO+MDR). This paper leverages a GEO downlink simulation model to systematically investigate the power gain and spectral-efficiency gain achieved by AO, MDR, and their combined approach across various turbulence intensities. A key focus is a systematic examination of the interaction mechanisms within the AO+MDR method. Notably, we establish a novel finding: within the AO+MDR framework, AO and MDR exhibit a mutually weakening effect under weak turbulence, while demonstrating a mutual enhancement under strong turbulence. This significant observation has been further corroborated through desktop experiments.