Coherent amplification of peak-power-scalable out-of-phase supermode in Yb-doped multicore fiber

We demonstrate selective excitation and coherent amplification in multicore fiber of the out-of-phase supermode that has equal intensities but interleaved 0/π phases in the neighboring cores. The out-of-phase supermode is beneficial due to its stability at arbitrary high powers, contrary to the fundamental supermode. We fabricated a double-clad all solid silica fiber with six highly Yb-doped coupled cores arranged in a ring structure. We obtained amplification of 50 picosecond chirped pulses up to ~1 μJ energy with measured content of the out-of-phase mode of >80%. We demonstrated in 3D numerical simulation the possibility of the out-of-phase supermode amplification for powers up to damage threshold in silica glass.