High-power 2.04  μm laser in an ultra-compact Ho-doped lead germanate fiber

A highly Ho-doped single-mode lead germanate glass fiber is developed for compact ∼2  μm lasers. Over 600 mW of laser output operating at 2.04 μm is demonstrated in a 2 cm-long active fiber. The slope efficiency reaches ∼34.9% with respect to the launched 1.94 μm laser pump power. To the best of our knowledge, this is the highest laser output power demonstrated within a few centimeters of a Ho-doped fiber. This result shows that the fiber is highly promising for high-power single-frequency laser applications.