2.05 μm holmium-doped all-fiber laser diode-pumped at 1.125 μm

We report a holmium-doped all-fiber laser oscillating at similar to 2.05 mu m in continuous wave at direct in-core pumping by a 1.125 mu m laser diode. Two types of home-made holmium-doped alumino-germano-silicate fiber (HDF), differentiated in the Ho3+ doping level, were fabricated to implement the laser, for revealing the effect of Ho3+ concentration upon the laser output. Firstly, the fibers were characterized thoroughly from the material and optical viewpoints. Then, laser action with both HDFs was assessed using the simplest Fabry-Perot cavity, assembled by a couple of spectrally adjusted fiber Bragg gratings, also made-in-house. In the best case, when using the lower-doped HDF of proper length (1.4 m), low threshold (similar to 370 mW) and moderate slope efficiency (similar to 13%) of similar to 2.05 mu m lasing were obtained at 1.125 mu m diode pumping. Long-term stability, high brightness, low noise, and purely CW operation are shown to be the laser's attractive features. Yet, when utilizing the heavier-doped HDF, laser output is revealed to be overall worse, with a possible reason being the deteriorating Ho3+ concentration-related effects.