Thulium-doped optical fibers and components for fiber lasers in 2 µm spectral range

Thulium-doped fiber lasers are attractive light sources in the infrared region at around 2 micrometers. Their slope efficiency may reach 70 % and thus they are challenging the well-established ytterbium-doped fiber lasers operating at around 1 micrometer. Two-micrometer radiation sources have many advantages over the one-micrometer sources, e.g., better eye-safety, relaxed non-linear limits and more efficient material processing for some types of materials. Particularly important applications of lasers at 2 micrometers are in nonlinear frequency conversion to mid-infrared wavelength. In this paper we review our recent progress in research of thulium-doped fibers and fused fiber components.