Space-division multiplexing: the next frontier in optical communication

TLDR

Space‑division multiplexing (SDM) increases optical communication capacity by exploiting multiple spatial channels and is applicable to both free‑space and guided‑wave systems. This paper investigates SDM in fiber‑optic links using few‑mode or multimode fibers, focusing on the critical challenge of mode crosstalk. The authors propose applying MIMO equalization from wireless communication to cancel mode crosstalk, augmenting it with optical techniques such as differential modal group delay management, strong mode coupling, and multicore fibers, while reviewing advances in passive devices (demultiplexers) and active devices (amplifiers, switches) to reduce computational complexity. The study concludes by outlining the prospects for SDM in future optical transmission and networking applications.

Abstract

Space-division multiplexing (SDM) uses multiplicity of space channels to increase capacity for optical communication. It is applicable for optical communication in both free space and guided waves. This paper focuses on SDM for fiber-optic communication using few-mode fibers or multimode fibers, in particular on the critical challenge of mode crosstalk. Multiple-input–multiple-output (MIMO) equalization methods developed for wireless communication can be applied as an electronic method to equalize mode crosstalk. Optical approaches, including differential modal group delay management, strong mode coupling, and multicore fibers, are necessary to bring the computational complexity for MIMO mode crosstalk equalization to practical levels. Progress in passive devices, such as (de)multiplexers, and active devices, such as amplifiers and switches, which are considered straightforward challenges in comparison with mode crosstalk, are reviewed. Finally, we present the prospects for SDM in optical transmission and networking.