Ultra-low-crosstalk multicore fiber-integrated pump-signal combiner for a core-pumped EDFA.

Fiber-integrated, submersible-qualified, core-pumped, multicore EDFAs are indispensable for space-division-multiplexing envisioned for the next generation of submarine communication lines. Here we demonstrate a fully packaged, 63-dB counter-propagating crosstalk, and 70-dB-return-loss four-core pump-signal-combiner. This enables core-pumping of a four-core EDFA.