Single-Mode Fiber Coupling with Adaptive Optics for Free-Space Optical Communication under Strong Scintillation

The need for space-ground data transmission systems with high data throughput has encouraged the development of new satellite-to-ground laser links, using adaptive optics to compensate for the deleterious effects of atmospheric turbulence. On the ground segment, the use of single-mode fiber components, and thus the coupling of the propagating signal into a single-mode fiber, is strongly favored. However, the single-mode fiber coupling efficiency and the resulting data rate are strongly hampered by the turbulence-induced phase distortions and amplitude fluctuations (called "scintillation"). The effects of scintillation in the pupil are the strongest at low elevations of Low Earth Orbit satellites-to-ground links and are not compensated by traditional adaptive optics, which correct only the phase of the distorted signal. In this paper, we assess the effects of AO correction on the statistical properties of single-mode fiber coupled flux based on experimental data obtained in the presence of medium and strong scintillation. We show preliminary results of coupled flux, as well as their temporal variations and probability distribution, for different adaptive optics correction levels.