High efficient single-end operation Tm-doped silica fiber laser based on intracore FBGs

A LD-clad-pumped single-end operation Tm-doped silica fiber laser was reported. The output center wavelength was located at nearly 1.96 μm, and the maximal output power was 2.41 W with a 7.2 W threshold and 37.7% slope efficiency respected to the launched pump power. The laser cavity was made up only by the multi-mode FBGs, which was directly written into the 25/250 μm double-clad Tm-doped multi-mode fiber core using an 800 nm femtosecond laser and a phase mask. There was no output coupler at the other fiber end, which was angle-polished (40.4°) to suppress the fiber end Fresnel reflection. The out-put power characteristics were investigated with variable angle-polished fiber end as output coupler, such as: 0°, 5.4°, 25.5°, and 40.4°. With the increasing of fiber end polished angle, the fiber laser output slope efficiency almost held invariable, and the fiber laser only had a increasing of threshold. The output laser spectrum had no change at different polished angles.