Effects of atmospheric turbulence on fiber-coupled DPSK system in Satellite-to-Ground downlink

Fiber-coupled differential phase-shift keying (DPSK) modulation is potentially an effective approach for further high-speed satellite lasercom, due to the high detection sensitivity, low linewidth requirements, and uncalled-for complex phase-locked loop techniques. Nevertheless, the phase distortion caused by atmospheric turbulence will destroy the spatial coherence of the incident light field, thereby limiting the coupling efficiency of spatial light to single-mode fiber. Here, we report on the effects of atmospheric turbulence on fiber-coupled DPSK system in Satellite-to-Ground (STG) downlink. Fading characteristics of receiving signals and average BER performances have been also studied to optimize DPSK system performances by using wavefront modal compensation method based on orthonormal polynomials. An optimal receiving aperture could be obtained to achieve lowest BER in finite items of mode compensation. The analysis results can provide a reference for optimization of the receiving aperture in the STG downlink laser communication system and the reasonable system margin design.