High coupling efficiency and low signal light loss (2 + 1) × 1 coupler**Project supported by the National Natural Science Foundation of China (Grant No. 61307057) and the Fund from the State Key Laboratory of Tribology, Tsinghua University (Grant No. SKLT12B08).

Abstract

The coupling efficiency of the pump coupler determines the pump light injection capacity of a laser system. Experimental analysis of the influences of different factors on the pump coupling efficiency is in accordance with this conclusion. We use two Nufern fibers (400 μm/440 μm with NA = 0.22) as pump arm, one Nufern fiber (20 μm/400 μm with NA = 0.06/0.46) as a main fiber to make a side-pumping (2+1)× 1 coupler. The experimental result shows that the total output power of this (2+1)× 1 coupler is about 1160 W, corresponding to a coupling efficiency as high as 98.6%. The loss of signal light is less than 1%.