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A Five-Mode Erbium-Doped Fiber Amplifier for Mode-Division Multiplexing Transmission

We describe a few-mode erbium-doped fiber amplifier with ring-doped erbium doping profile fiber and optimized optical setup amplifying LP01, LP11, and LP21 modes, simultaneously. Spectral and modal gain distribution is characterized as well as modal crosstalk. We study the gain evolution of every mode in several configurations, changing the input power or the number of injected modes. The gain is above 13 dB for all modes and its differential modal gain is lower than 5.7 dB across the whole C-band with a 3.5-m-long erbium-doped fiber when using a pump at 630 mW. As a proof of concept, we transmit up to five modes carrying each a PDM-QPSK signal at 32 Gbd through this amplifier.