Pilot beam-assisted adaptive compensation for atmospheric turbulence in free-space optical transmission of beams carrying orbital angular momentum

One of the major challenges for free-space optical (FSO) communication through atmosphere is the turbulence caused by the random variations in temperature and convective motion of air. It induces fluctuation in intensity and phase of the propagating optical signal and impairs the transmission quality. The FSO communication using beams carrying orbital angular momentum would be vulnerable to such fluctuation since they have a unique spatial phase profile of the helical phase front. In order to overcome the issue, we propose a pilot beam-assisted adaptive compensation method for the turbulence-induced phase fluctuation by using spatial light modulators and a wavefront sensor. The proposed method is a potential candidate for real-time compensation due to its fast operation without algorithmic converging process. The propagation of Laguerre-Gaussian beam through atmospheric turbulence is numerically analyzed based on the modified von Karman model and split-step beam propagation method. The simulation results reveal that the compensation performances are considerably improved by using the pilot beam which has the same azimuthal index as that of the data beam. (C) 2020 The Japan Society of Applied Physics.