Space-division multiplexing (SDM) systems has been the subject of much research during the past decade as a way to overcome the capacity limit of current single-mode fiber (~100 Tbit/s). The main focus is oriented towards mode-division multiplexing transmission over few-mode fibers as a one of SDM approach and the design of energy efficient few-mode erbium doped fiber amplifier (FM-EDFA) for SDM long haul systems. The main objectives of this book is to study the performance of the FM-EDFAs in an optical SDM systems by using an appropriate pump field intensity distribution and an erbium doped fiber with a tailored erbium-doped profile.