Reconfigurable Modal Gain Control of a Few-Mode EDFA Supporting Six Spatial Modes

We experimentally demonstrate an inline few-mode erbium doped fiber amplifier supporting six spatial modes with reconfigurable differential gain control and excellent gain flatness obtained through mode-selective bidirectional pumping of a custom fiber with a radially profiled erbium dopant distribution. A signal gain of
${>}{\rm 20}~{\rm dB}$
was obtained for all the guided modes with a differential modal gain
${<}{\rm 2}~{\rm dB}$
and good gain flatness across the C-band.