**Abstract**

Space division multiplexing (SDM) over fibers has introduced a new paradigm in optical communication thanks to its capability to meet the ever-renewed demand of more transmission capacity and on large spectral efficiency. This ever-increasing demand is pushed by the nonstop increase of the number of connected users, devices, processes, and data (toward internet of everything IOE). One of the most promising variants of SDM, that has recently shown great potential, is based on harnessing orbital angular momentum (OAM) modes as data carriers. These OAMs are multiplexed, transmitted over special optical fibers (OAM-fibers) then de-multiplexed. In order to highlight the potential of SDM system incorporating OAM modes through fibers, in this chapter, we disassemble an SDM system and we examine its main key elements. The potential of OAM-SDM is discussed as a promising candidate for the next generation local/global communications networks. This chapter is intended to provide a comprehensive and deep understanding of SDM, which will push R&D community to derive future research directions in the field.

**Keywords:** optical communication, space division multiplexing (SDM) systems, orbital angular momentum (OAM), optical fibers
