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A multiwavelength tunable fiber laser operating at 1.9 µm is demonstrated. A 4 m long Tm-doped single-mode fiber is pumped by a 1.57 µm fiber laser. A Sagnac fiber loop is used in the fiber laser cavity as a tunable filter, and the fiber loop consists of a 3-dB coupler, a polarization controller (PC), and a segment of polarization-maintaining fiber. Adjusting the PC state and pump power, multiwavelength laser with wavelength spacing of 2.5 nm 1895–1915 nm is observed. The number of output wavelength can be tuned precisely from one to four by adjusting the PC state. The 3-dB linewidth and side-mode suppression ratio are 0.045 nm and 45 dB, respectively. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:401–403, 2015

We propose an all-fiber source at 3.8 μm with a high Tm-doped fiber as the gain medium pumped by a 1565-nm high-power fiber laser. With a laser diode at 1565 nm amplified by a high power erbium-doped fiber amplifier injecting into a segment of Tm-doped fiber, a fiber laser at 3.8 μm generates. Simultaneously, a second-order laser at 1.9 μm (dual-frequency of 3.8 μm) can be observed clearly. The laser has a threshold pump power of ∼300 mW and generates more than 176 mW continuous-wave output power with 1560 mW pump power. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:848–850, 2014