Beam quality analysis and optimization in an adiabatic low mode tapered fiber beam combiner

We study tapered fiber bundle based beam-combining structures that closely maintain their lowest supermodes in order to optimize the output beam quality. A method for efficiently producing structures with high beam quality is proposed. The method is based on monitoring the output powers of the tapered fiber bundle during fabrication and evaluating the beam properties at the central portion based on symmetry considerations. The method is demonstrated experimentally and supported by theoretical analysis. Several seven-fiber combiner configurations are demonstrated. The obtained beam qualities are close to the theoretical limits, as dictated by the brightness conservation law.