**5. Conclusions**

Multiplexing spatial modes (SDM) seems to be viable solution to cope with the upcoming capacity crunch. In this chapter, we attempted to focus on the different aspects from an SDM system (emission, transmission and reception) over optical fibers aiming to highlight their main key elements and components that allow this technology to be the desired one for next generation local/global optical communication systems/networks. We focused on the last trend of SDM communication research direction: OAM-SDM over optical fibers. We discussed the OAM modes and the main devices & schemes for the generation & detection and the transmission of them. OAM specialty fibers are highlighted with focus on, their key features, their main achievements (throughput & main contributions) and main challenges that face their progress. Perspectives and future research orientations that may touching SDM systems have been presented at the end of this chapter. From what we have attempted to present, SDM still unexhausted research area that optical communication R&D community have to derive/touch future research directions in the field.
