Few-mode fiber transmission with in-line few-mode erbium-doped fiber amplifier

We demonstrate wavelength-division multiplexed (WDM) and mode-division multiplexed (MDM) transmission over a fiber recirculating loop comprising of a 25-km span of low differential mode group dispersion (DMGD) few-mode fiber carrying the LP01 and LP11 mode groups, and an inline few-mode erbium-doped fiber amplifier (FM-EDFA) providing low mode-dependent gain (MDG) per span. We successfully transmitted a 10λ × 6 × 28-Gbaud QPSK signal over a distance of 700 km.