A Focusing Mirror-Based Atmosphere Turbulence Mitigation Technique for Orbital Angular Momentum with OFDM-IM in Free Space Optical Communications

Orbital Angular Momentum (OAM) communication has gained significant interest in Free Space Optical (FSO) communications due to its ability to multiplex multiple data streams onto different OAM modes, thereby significantly enhancing data transmission capacity. This inherent multiplexing capability of OAM allows for the simultaneous transmission of multiple channels over the same frequency. However, the propagation of OAM modes through free space is heavily impacted by atmospheric turbulence (AT), which induces signal attenuation and crosstalk, thus degrading system performance. This study aims to mitigate crosstalk and enhance bit-error rate by employing a focusing mirror and orthogonal frequency division multiplexing with index modulation (OFDM-IM) technique which offers improved spectral efficiency and bit-error rate (BER). Through numerical simulations, we demonstrate that the focusing mirror reduces crosstalk among OAM modes, improving the OAM-based FSO communication systems.