Multi-Watt Operation of a Holmium Doped Silica Fibre Laser at 2.2 μm

Laser sources operating in the atmospheric transmission window between 2.1 and 2.25 μm are of interest for a range of applications (e.g. remote sensing, free-space communication and defence). Holmium fibre lasers provide good coverage of the lower part of this spectral region [1], but operation towards 2.2 μm is much more challenging due to a reduced emission cross-section and higher propagation losses associated with the IR absorption edge of fused silica. Furthermore, OH
^-
-contamination can cause additional absorption around 2.2 μm. Here we investigate the limits of long-wavelength tuning of a holmium-doped fibre laser, and report, to the best of our knowledge, the first watt-level (4.1 W) output from a silica fibre laser operating at 2.2 μm.