Spatially and Spectrally Resolved Gain Characterization of Space-Division Multiplexing Amplifiers with Coherent Swept-Wavelength Reflectometry

We directly measure the spatially and spectrally resolved gain of erbium doped multi-core and few mode fiber amplifiers using a coherent swept wavelength interferometer operated in the reflection mode. It greatly simplifies the characterization of multi-spatial mode amplifiers because it enables characterization of the mode-dependent gain with only a single mode-selective multiplexer at the input. The gains for both multi-core fiber amplifier and 3 spatial mode (LP01 and LP11) amplifier are measured. Measurements for multi-core fiber amplifier are conducted using two pump schemes, core pump and cladding pump. Also, the comparison with the cutback experiments shows the validity of this technique.