Tunable holmium-doped fiber laser with multiwatt operation from 2025 nm to 2200 nm

The emission band of holmium-doped silica fibers extends beyond 2200 nm, which means these lasers have the potential of covering considerable parts of the atmospheric transmission window between similar to 2100 nm and 2250 nm. However, efficient operation toward 2200 nm is challenging due to absorption in fused silica at the laser wavelength. Here we present a holmium-doped fiber laser specifically targeting long-wavelength operation. The laser is implemented as a high-feedback wavelength selective ring cavity and is tunable from 2025 nm to 2200 nm. A maximum slope efficiency of 58% is obtained at 2050 nm and a slope of 27% is obtained at 2200 nm. A power of 5.5 W from a single aperture (8.9 W total) is demonstrated at 2200 nm. Our results represent extended coverage of the 2 mu m spectral band with multiwatt-level silica fiber lasers. (C) 2019 Optical Society of America