Watt-level 2.94μm Er: ZBLAN fiber laser with low threshold

We have successfully demonstrated a high-power erbium-doped fluoride glass fiber laser operating at 2.94 μm. The system achieved continuous operation with an output power of 7.1 W at 2.94 μm. The all-fiber Fabry–Perot laser cavity was constructed using an 11.5 m, 7 mol. % Er³⁺ :ZBLAN fiber with two fiber Bragg gratings (FBG) having reflectivities of 99.7% and 29.2%. These fiber Bragg gratings were inscribed using a 513 nm femtosecond (fs) laser direct-writing technique. To prevent deterioration at high output powers, an endcap was fused at the output fiber end. The system operated at 2.94 μm exhibited an overall slope efficiency of 20.5% in relation to the launched pump power at 980 nm, and demonstrated a single-mode output beam quality with M² < 1.2.