Multi-wavelength narrow linewidth thulium-doped fiber laser operating at 1.9μm using a tunable Sagnac fiber period filter

We demonstrate a tunable multi-wavelength thulium-doped fiber laser (TDFL). A Sagnac fiber period filter is employed to achieve the tunable multi-wavelength fiber laser and consists of a 3-dB coupler, a segment of 4 m long polarization maintained thulium-doped fiber (PM-TDF) and a polarization controller (PC). Multi-wavelength laser are observed in the wavelength region of 1.9 mu m, and the side-mode suppression ratio (SMSR) of the multi-wavelength fiber laser is over 55 dB with 1 W pump power at 1.56 mu m. By adjusting PC, tunable range of output laser spectrum from 1955 to 1962 nm can be obtained with single-wavelength laser. In addition, the linewidth of the laser is narrower due to the use of a fiber loop for suppressing multimode oscillation. This fiber laser around 1.9 mu m wavelength are useful mid-infrared laser generation, free space laser communications, medicine and biomedical, coherent laser radar for remote atmospheric sensing, pump for nonlinear frequency conversion based on soliton self-frequency shift and second-harmonic generation.