A 1.8-μm multiwavelength thulium-doped fiber laser based on a hybrid interference filter

A 1.8-mu m tunable multiwavelength thulium-doped fiber laser based on a hybrid filter is proposed. In the designed ring-cavity fiber laser, the filter consists of one Sagnac loop and one dual-pass Mach-Zehnder filter. In the experiment, the lasing threshold is 155mW, and a continuously tunable and stable single-wavelength laser could be realized with a minimum tuning interval of 2.1nm within a scope of 22.5nm. When an 1858-nm laser is obtained, the peak power fluctuation is less than 0.83dB within 20 minutes at room temperature. By adjusting the polarization controller, stable dual-wavelength lasers are simultaneously achieved, and the peak power shift is less than 1.24dB within a scan time of 20 minutes at room temperature. By changing the polarization state, stable triple-wavelength lasing is obtained, and the power fluctuation is less than 1.95nm. In the experiment, the 3-dB linewidth of the laser is less than 0.4nm.