Single-frequency DBR lasing by integrating FBGs into germanium-free photosensitive highly Yb3+-doped silica fiber

Yet, the doping level of rare-earth (RE) ions has generally to be sacrificed in the classical Ge-photosensitized RE-doped silica fibers because of the dramatic refractive index increase caused by the introduction of Ge.

Here, we demonstrate an approach to realize the trade-off between photosensitivity and RE doping concentration. We validate that the addition of a small amount of cerium (0.37wt.%) instead of Ge could photosensitize Yb3+-doped silica fiber (YDF), while maintaining fiber numerical aperture (NA) at 0.12 under a high 2.5-wt.% Yb doping level. Based on the short monolithic DBR cavity constructed by this germanium-free photosensitive highly YDF, a 1064 nm fiber laser with a 48.6% slope efficiency and an over 200 mW power on two orthogonally polarized modes could be realized.