Space‐Division Multiplexing and MIMO Processing

This chapter first describes various optical fibers that can support space‐division multiplexing (SDM) transmission. It then reviews SDM transmission techniques that can be utilized in case the crosstalk between the spatial channels is small, for example, in multi‐core fibers (MCFs). The chapter also introduces the general principles for SDM transmission over optical fibers in the presence of coupling between the spatial channels, describes the basic properties of the fiber‐optic multimode channel, such as differential group delay (DGD) and mode‐dependent loss (MDL), as well as the strategies to reduce the impact of the DGD. It further discusses experimental results for multiple‐input multiple‐output (MIMO) transmission and MIMO digital signal processing (DSP) techniques specific to SDM systems. The second part of the chapter describes methods for SDM component characterization and components required for SDM transmission systems such as mode couplers, SDM wavelength‐selective switches (WSSs), and SDM optical amplifiers.