Performance metrics and design parameters for an FSO communications link based on multiplexing of multiple orbital-angular-momentum beams

We investigate the design parameters for an OAM multiplexing-based free-space optical data link by analyzing power loss, channel crosstalk, and power penalty of the link, considering the misalignment between the transmitter and receiver (displacement, angular error, or their combination). Given a specific link distance, a transmitted beam size design approach is suggested. In addition, we also provide a trade-off approach to design proper transmitter and receiver aperture sizes and mode spacing of the transmitted OAM beams under a certain displacement or angular error. Our simulation indicates that (1) system with a larger beam size and a larger aperture seems to be more tolerant to the displacement but less tolerant to the receiver angular error. (2) system with a small mode spacing shows lower system power penalty under a small displacement or receiver angular error, while a larger mode spacing shows lower power penalty when the displacement or receiver angular error is above a certain threshold.