Tm3+-doped silica fiber laser output at 1.94μm with multi-mode FBG as cavity

Abstract

An all-fiber LD-clad-pumped Tm-doped fiber laser was reported, and the CW maximal output power reached 24W at nearly 1.94µm. The homemade double-clad Tm 3+ -doped fiber had a demission of 25/250µm with the core NA 0.13 and inner-clad NA 0.46. A matched passive multi-mode FBG acted as the front cavity. The cavity was build-up by the high reflectivity FBG and fiber end Fresnel reflectivity. The all-fiber scheme was build-up by splicing the pigtail fiber, FBG fiber and Tm 3+ -doped fiber. Cooling by the water, the 56% high slope efficiency was achieved and threshold was 6.4W, respected to the launched pump power. When the output power was less-than 3W, the output laser was single-peak operating at 1936.4 nm with a very narrow linewidth (50 pm) laser output. Increasing the launched pump power, the output laser wavelength grew to 3~4 peaks. The multimode fiber Bragg grating (FBG) transmission spectrum was also measured with a matched 82cm Nufern Tm 3+ -doped fiber as fluorescent sources. With the dichroic and the FBG building up cavity, the output laser characteristics were also investigated. Because the multi-mode FBG reflectivity was not very high, both ends of the fiber laser had laser output power, and the ratio was nearly 10:1. As we know, it was the first time to report the multi-mode FBG all-fiber laser. Under this simple Tm 3+ -doped fiber laser scheme, we estimated that the maximal output power could reach several ten watts.