All-fiber 7×1 pump combiner for high power fiber laser

•Influence of taper and its waist lengths on pump combiner is analyzed.•A pump combiner is fabricated with 98.4% efficiency and 3.81 kW output power.•The fabricated combiner delivers the highest pump power at present.

We investigate N×1 pump coupler theoretically and experimentally. Firstly the influence of lengths of the transitional region and the waist region of tapered fiber bundle on the efficiency of a 7×1 pump combiner is numerically analyzed. The results suggest that there is a minimum length for the transitional region in order to achieve high efficiency; meanwhile, the waist region should be as short as possible. Then a 7×1 pump combiner is fabricated. The transmission efficiencies of all 7 ports are higher than 98% and the final total output power is as high as 3.81 kW with 98.4% transmission efficiency. This is the highest output power reported to date and improvement further is possible by better cleaving, splicing and using LD with higher power. The experimental result verifies the simulation which can be applied in the fabrication of N×1 pump combiners.