2.05-μm Holmium-doped all-fiber continuous-wave laser at in-core diode-pumping at 1.125 μm

We report a Holmium-doped all-fiber laser oscillating in continuous-wave at ~2.05 μm, at in-core pumping by a 1.125-μm laser diode. The active fibers employed are alumino-germano-silicate fibers doped with Ho3+ at concentrations of ~1.2×1019 and ~1.8×1019 cm-3. The laser is implemented in non-optimized Fabry-Perot cavity’s geometry, composed of a couple of fiber Bragg gratings with reflectivity of 99 and 90%. When using the lower doped Holmium-doped fiber of proper length (1.4 m), low threshold (~370 mW) and moderate slope efficiency (~13%) of ~2.05-μm lasing were obtained. High-brightness (laser line’s width is ~60 pm) and good noise-to-signal ratio (<0.006) are the laser’s attractivities. In case of the heavier doped fiber of optimal length (1.2 m), the laser output (threshold of ~430 mW, slope efficiency of ~9%, output power of ~9 mW, laser line’s width of 110 pm, noise-to-signal ratio of <0.009) is worse, with a probable reason being deteriorating Ho3+ concentration effects.