1.7 W holmium-doped fluoroindate fiber laser at 3920 nm

A monolithic fiber laser emitting 1.7 W at 3920 nm is experimentally demonstrated in a Ho³⁺:InF₃ fiber. The cavity comprises a pair of highly reflective fiber Bragg gratings written in the active fiber with the femtosecond phase-mask scanning technique and is spliced to the pump diode with a robust silica-to-fluoride fiber splice. This work is an important step toward high-power all-fiber laser operating in the vicinity of 4 µm.