Field Conjugation Adaptive Arrays in Free-Space Coherent Laser Communications

We analyze the performance of adaptive field conjugation array receivers in coherent laser communications through the turbulent atmosphere. We consider coherent fiber arrays consisting of densely packed multiple subapertures, with each subaperture interfaced to a single-mode fiber. In a field conjugation fiber array, the single-mode fiber outputs are detected, and the photocurrents are adaptively co-phased and scaled, and then summed to mitigate signal fading associated with atmospheric turbulence and compensate for imperfect fiber coupling efficiency. We quantify how field conjugation processing improves performance in the presence of turbulence, as compared to a monolithic-aperture coherent receiver having an equal total cross-sectional area.