Adaptive compensation for the angular deflection of beams carrying orbital angular momentum on mode sorting

Beams carrying orbital angular momentum (OAM) have attracted attention as a potential candidate to expand the transmission capacity in the optical communication. Mode sorting is an efficient method to demultiplex the OAM multiplexed lightwaves. We have reported the mode sorting performance for OAM beams suffering lateral displacement and angular deflection. It was found that the angular deflection was severe, namely, only 100- rad deflection deteriorated the performance in terms of crosstalk. Thus, the strict angular alignment would be required in the free-space optical communication using OAM multiplexing. In this paper, we propose an adaptive compensation method based on the detection of the angular deflection of beams carrying OAM on mode sorting in order to relax such a strict requirement. Numerical simulation results reveal that the compensation in every 100 rad effectively suppresses the crosstalk caused by the angular deflection.