Analysis of the orbital angular momentum spectrum for Laguerre-Gaussian beams under moderate-to-strong marine-atmospheric turbulent channels

Free-space optical (FSO) communication based on orbital angular momentum (OAM) can be used to enhance the capacity of systems for vessel-to-vessel or ship-to-aircraft communication. Studying the OAM spectrum is important for analyzing the performance of FSO-OAM communication systems under marine-atmosphere channels. This study offers a new, concise form for the OAM spectrum for Laguerre-Gaussian (LG) beams propagating under moderate-to-strong marine-atmospheric turbulent channels with high accuracy. We use a concise expression to analytically investigate the rules governing the variation in the OAM spectrum versus OAM number, distance, refractive-index structure parameter, and wavelength. We demonstrate that broadening of the OAM spectrum caused by marine-atmospheric channels can be analytically studied based on a simplified expression. The results indicate that an increase in the transmitted OAM number, distance and refractive-index structure parameter exacerbates broadening of the OAM spectrum and that using a larger wavelength relieves such broadening. This data contributes to the analysis of FSO-OAM multiplexing communication systems under marine-atmospheric turbulent channels and the design of future over-the-sea communication systems.