Fractal, Diffraction-encoded Space-Division Multiplexing for Free Space Optical Communication

Abstract

With free space optical (FSO) systems, information is generally transmitted to minimize diffraction. Here, we demonstrate an alternate paradigm in which multiple spatial bit streams are diffraction-encoded, an approach that enables a wider cone for reception and is especially robust to noise. We leverage the fact that diffracted fractal patterns or diffractals redundantly encode information over large areas as they propagate to the far field. This scheme enables a roving receiver to capture multiple spatial bits simultaneously when sampling a portion of the far-field beam. Our numerical FSO studies with and without atmospheric turbulence are a basis for new design considerations governing roaming area, beam divergence, and proper diffraction encoding. Concepts related to the sparse complexity of fractal, diffracted patterns show promise for diffractal space division multiplexing and may also be applied to channel marking, sensing, imaging, and other FSO systems.