All-fiber 6-mode multiplexers based on fiber mode selective couplers

All-fiber 6-mode multiplexer composed of two consecutive LP11-mode selective couplers (MSC), two LP21-MSCs and an LP02-MSC is characterized by wavelength-swept interferometer. A pair of the multiplexers has minimum mode dependent loss of 4 dB and high mode group selectivity of over 15 dB. Mode division multiplexed transmission enabled by the all-fiber multiplexers is demonstrated over fiber spans of 117 km employing an in-line multimode optical amplifier. 6 modes of 120 Gb/s dual polarization quadrature phase shift keying signals combined with 30 wavelength channels are successfully transmitted