Detection of Free-Space Optical Orbital Angular Momentum Modes Based on GS Algorithm

In free-space optical (FSO) communications, orbital angular momentum (OAM) provides extra degrees of freedom to improve spectrum efficiency by multiplexing a set of orthogonal modes on the same wavelength channel. To recover the information carried on the optical OAM modes correctly, the receiver has to first know which OAM modes are transmitted. In this paper, we first present the atmospheric turbulence channel model and the FSO system model. Then, we propose an OAM mode detection method based on Gerchberg-Saxton (GS) algorithm from the perspective of optical signal processing, rather than using additional optical components. Simulation results show that the proposed GS algorithm-based detection method is able to restore the vortex phase of multi-mode multiplexed Laguerre-Gaussian (LG) beams in weak and medium atmospheric turbulence cases, and the optical OAM modes could be detected with the recovered vortex phase.