Ring-Core Multicore Few-Mode Erbium-Doped Fiber Amplifier

In this letter, we demonstrate a seven-core few-mode erbium-doped fiber amplifier by core pumping for long-haul transmission system using a few-mode multicore fiber. The differential modal gain between the LP01 and LP11 modes is reduced to 3.2 dB or less regardless of the pumping-light mode using a ring-core refractive-index profile, and flattened averaged gains of over 20 dB and noise figures of less than 7 dB for all cores and all modes of the input light are achieved in the C-band. The inter-core crosstalk between the center and outer cores has a very low value of -49 dB or less at a wavelength of 1560 nm.