Crystal-derived double-clad fibers for high gain and high efficiency Tm fiber lasers

We investigate Tm-doped double-clad fibers drawn from fused silica preforms with inserted Tm:YAG laser crystal rods. Based on the Molten-Core-Method the drawn crystal-derived fibers show typical amorphous properties covering a Tm concentration range from 0.2 to 0.84 mol% Tm2O3. They are studied in terms of their suitability of for multi-Watt level fiber lasers and compared to a Tm-laser fiber conventionally fabricated by Modified Chemical Vapor Deposition and solution doping. For the crystal-derived fibers, we demonstrate up to 4 W output power around 2 μm emission wavelength and a slope efficiency of 47 %, which are to date the highest achieved values for 790 nm pumping.