Multiplexing schemes for optical communication through atmospheric turbulence

TL;DR

This paper explores how MIMO and OAM multiplexing schemes are related in free-space optical communication and analyzes the impact of atmospheric turbulence on these modes, revealing their similarities and limitations.

Contribution

It demonstrates the equivalence of MIMO and OAM modes under certain conditions and studies turbulence effects using phase screen simulations.

Findings

MIMO and OAM modes are closely related for circular apertures.

Usable singular modes correspond to Laguerre-Gauss vortex beams with specific radii.

Atmospheric turbulence significantly affects the integrity of these communication modes.

Abstract

A central question in free-space optical communications is how to improve the transfer of information between a transmitter and receiver. The capacity of the communication channel can be increased by multiplexing of independent modes using either: (1) the MIMO (Multiple-Input-Multiple- Output) approach, where the communication is done with modes obtained from the singular value decomposition of the transfer matrix from the transmitter array to the receiver array, or (2) the OAM (Orbital Angular Momentum) approach, which uses vortex beams that carry angular momenta. In both cases, the number of usable modes is limited by the finite aperture of the transmitter and receiver, and the effect of the turbulent atmosphere. The goal of this paper is twofold: First, we show that the MIMO and OAM multiplexing schemes are closely related. Specifically, in the case of circular apertures, the usable singular modes of the transfer matrix are essentially the same as the commonly used Laguerre-Gauss vortex beams, provided these have a special radius that depends on the wavelength, the distance from the transmitter to the receiver and the ratio of the radii of their apertures. Second, we study the effect of atmospheric turbulence on the communication modes using the phase screen method put in the mathematical framework of beam propagation in random media.