Misalignment tolerance enhancement of vector beams in a free-space optical communication link

Optical misalignment between transmitter and receiver leads to power loss and mode crosstalk in a mode division multiplexing (MDM) free-space optical (FSO) link. We report both numerical simulations and experimental results on the propagation performance of two typical vector beams, C-point polarization full Poincaré beams (FPB), and V-point polarization cylindrical vector beams (CVB), compared to homogeneous polarization scalar vortex beams (SVB) under optical misalignment. The FSO communication performance under misalignment using different transmit beams is evaluated in terms of power loss, mode crosstalk, power penalty, etc. Vector beams are shown to have superior misalignment tolerance compared to the corresponding SVBs, with the FPBs in particular being the most robust for small topological charges. At the same mode spacing, the CVBs have a larger misalignment tolerance, which causes the MDM-FSO communication systems with narrower mode spacing to have a smaller power penalty. Furthermore, moderately increasing the transmitted beam size could improve the system tolerance of lateral displacement while reducing that of tilt error.