Mid-infrared laser emission in heavily Er³⁺ doped double cladding ZBYA fibers

We report, to the best of our knowledge, the first demonstration of Er³⁺ doped ZrF₄-BaF₂-YF₃-AlF₃(ZBYA) glass fiber operating at 2.8 µm. The double cladding ZBYA fiber was fabricated by using the rod-in-tube method and the Er³⁺ ions concentration is 70000 ppm. Under the dual-end pumping of 976 nm LDs, the maximum unsaturated output power of 6.74 W was obtained in a 231 cm long gain fiber with a total slope efficiency of 15.2%. The thermal load can be effectively distributed through the application of double-cladding fibers and appropriate pumping methods. The dependence of slope efficiency and laser threshold on gain fiber length for dual-end-pumping was also investigated. This work may pave the way for a powerful 2.8 µm fiber laser with high robustness.