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 multicore and few mode fiber amplifiers using a coherent swept wavelength interferometer operated in the reflection mode. It greatly simplifies the characterization of multispatial 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 multicore fiber amplifier and three spatial modes (LP 01 and ${\rm{LP}}_{{11}}$ ) amplifier are measured. Measurements for multicore 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.