Air-Clad Holmium-Doped Silica Fiber Laser

We report the design, fabrication, and operation of an air-clad holmium-doped fiber laser that was manufactured by directly milling the rare-earth-doped preform. This silica fiber laser operates at 2.1
$\mu \text{m}$
with a slope efficiency of 49.7%, and is in-band pumped with a 1.94-
$\mu \text{m}$
thulium fiber laser. To the best of our knowledge, this is the first demonstration of an air-clad holmium-doped fiber laser.