A single-longitudinal-mode thulium-doped fiber laser using Fabry-Perot (F-P) filter and saturable absorber is proposed and experimentally demonstrated at the 2 μm band. In the structure, the combination of a narrowband F-P filter and a section of unpumped thulium-doped fiber ensures the single-longitudinal-mode lasing operation. A stable lasing operation is obtained at room temperature, with the central wavelength of 1941.6 nm and the optical signal-to-noise ratio of 32 dB. For an experimental period of 100 min, the output power fluctuates less than 1.5 dB and the center wavelength shifts less than 0.04 nm, indicating that the single-longitudinal-mode thuliumdoped fiber laser possesses good long-term stability.

thulium-doped fiber laser  /  Fabry-Perot filter  /  saturable absorber  /  single longitudinal mode