CO 2 -laser-ablation-assisted fabrication of signal-pump combiners with chirally coupled core fibers for co- and counter-pumped all-fiber amplifiers.

We report on the development of a side-fused signal-pump combiner with an integrated feed-through 34/250-µm chirally coupled core fiber. The manufacturing process involves a novel rotationally symmetrical cladding restructuring using a CO ₂ -laser beam. The signal-pump combiner exhibits the pump-to-signal fiber coupling efficiency of 90%, signal-to-pump isolation of 30 dB, and is high-power tested at a pump input power of >500 W. Additionally, a signal feed-through loss of 0.23 dB is measured and the S ² -method is used to confirm non-degradation of the spatial modes. The side-fused combiner technique has the advantage of an uninterrupted signal core and can be used in co- and counter-pumped configurations.