Low beam quality degradation, high-efficiency pump and signal combiner by built-in mode field adapter.

A low beam quality degradation, high-efficiency (6+1)×1 pump and signal combiner based on an end-pumping technique was realized by a built-in mode field adapter. A 2D simulation model to calculate the taper ratios of signal input and output fibers for matching the mode field profile in the coupling region was established. Based on the simulation results, we fabricated a combiner, achieving a signal coupling ratio of 87.52% and an average pump coupling ratio of 98.56%. The beam quality degradation caused by the signal feed-through of the combiner was theoretically determined in terms of the well-known M parameter and experimentally measured to be only ΔM=0.15 (1.05 to 1.2). Theoretical results are in good agreement with the experimental results.