Passive matching of large nonlinear phase in ultrafast twin-core fiber amplifier for coherent combination

Abstract

We use a bespoke design and fabrication procedure to realize a polarization-maintaining Yb-doped fiber with two near-identical, un-coupled, cores, suitable for coherent beam combination (CBC) of ultrashort pulses at large nonlinear phase accumulation. Using an in-house Dammann grating for seeding the two cores from a common input, we experimentally evaluated parabolic pulse amplification at 1064 nm. From a measured output interference pattern at a B-integral of 26 rad ± 15% according to simulations, we calculated a theoretical CBC efficiency of 88.5%, which to our knowledge is unprecedented with such high nonlinear phase. This suggests an averaged difference in B between channels of at most 0.5 rad (1.9% of 26 rad). Also, the 27 nm spectral width requires better than 17 μm optical path-length (OPL) matching. The OPL and B-integral remained stably equalized as B increased to 26 rad, suggesting that multicore fibers with carefully fabricated cores are well suited to power and energy scaling through CBC of pulses at high nonlinearity.

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Identifiers

ORCID for Huaiqin Lin: orcid.org/0000-0002-9805-4570

ORCID for Yujun Feng: orcid.org/0000-0001-7839-065X

ORCID for Jonathan H.V. Price: orcid.org/0000-0003-0256-9172

ORCID for Jayanta K. Sahu: orcid.org/0000-0003-3560-6152

ORCID for Johan Nilsson: orcid.org/0000-0003-1691-7959

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