Ge-As-S chalcogenide fiber combiner for efficient mid-infrared power scaling

A fiber combiner is a flexible optical component that can superimpose the power of multiple lasers to yield much higher output power than the available power from a single laser source. In this work, we report the design, fabrication, and characterization of a high-efficiency mid-infrared 3 × 1 chalcogenide glass fiber combiner. For the first time, the fiber combiner has been fabricated based on Ge-As-S glass, which has a significantly higher damage threshold than the conventionally used As-S glass. A power combining experiment has been carried out on the fabricated Ge-As-S glass fiber combiner at mid-infrared wavelengths. The input and output fibers of the combiner have core diameters of 100 µm and 220 µm, respectively. The taper ratio is 2, while the taper transition length is 10 mm and the waist length is 5 mm. The measurement shows that the power combining efficiency of the fiber combiner is ∼75.1% at 4.6 µm and ∼77.0% at 2 µm, respectively. When each of the three input fibers is launched with a 6 W 2-µm laser simultaneously with a coupling efficiency of ∼64.2%, a total power of 8.9 W is obtained from the output fiber. To the best of our knowledge, this is the highest recorded output power from a mid-IR fiber combiner. It has, therefore, demonstrated the promise of Ge-As-S chalcogenide fiber combiners for efficient mid-infrared 2-5 µm power scaling.