Holmium-doped optical fibers for efficient fiber lasers

Holmium-doped silica-based optical fibers belong to intensively studied materials for fiber laser sources operating around 2.1 μm. In this contribution, we deal with silica-based optical fibers doped with holmium and aluminum oxide. The fibers were prepared by the modified chemical vapor deposition method combined either with a solution doping or a nanoparticle doping. A large set of fibers with various dopant concentrations was characterized related to their fluorescence lifetime, laser threshold and slope efficiency. The best-performance fibers exhibited a fluorescence lifetime longer than 1 ms, a laser threshold under 200 mW and a slope efficiency around 80%. These characteristics are discussed regarding the doping method and dopant concentrations.