“…Further the strong modal overlap in MMFs can be used to build efficient multimode amplifiers where all spatial-modes are amplified at the same time similarly to the way optical amplifiers are used to amplify multiple wavelength channels in wavelength-division multiplexed (WDM) systems. Additionally, wavelength-selective switches (WSS) that support multiple modes, while maintaining a complexity comparable to traditional SMF WSS, have recently been demonstrated [2,3]. Mode-division multiplexing, however, also presents some formidable challenges, like mode coupling and mixing in optical components and MMFs, differential group-delay (DGD) spread present between the fiber modes, and differential attenuation of higher order modes nearer to the cladding index resulting in loss of capacity.…”