Performance of Oceanic Wireless Optical Communication Systems Based on Orbital Angular Momentum Multiplexing with Spatial Diversity

In oceanic wireless optical communication systems based on orbital angular momentum multiplexing, oceanic turbulence will bring the channel crosstalk. To solve the problem of channel crosstalk, a spatial diversity mitigation scheme is proposed. Random phase screen method is used to simulate phase perturbation caused by ocean turbulence and split-step transmission method is used to simulate the beam diffraction. Equal gain diversity combination is used to process signal at the receiver. 4 orbital angular momentum-multiplexed channels and 8-spatial diversity are used in the system. The influences of orbital angular momentum mode sets, oceanic turbulence strength and communication distance on the bit-error rate are investigated. Simulation results show that bit error rates decrease obviously with the modes spacing increases from 1 to 2 in the orbital angular momentum multiplexed sets. Performances of bit-error rates remain steady as modes spacing become larger. Bit-error rate will also increase with the increasing transmission distance and turbulence strength. Results show using diversity combination on orbital angular momentum-multiplexed systems can effectively mitigate the performance degradation from oceanic turbulence.