A Novel Switchable and Tunable Dual-Wavelength Single-Longitudinal-Mode Fiber Laser at 2

A switchable and tunable dual-wavelength single-longitudinal-mode (SLM) fiber laser in a 2- $\mu \text{m}$ region based on saturable absorber and self-injection locking is proposed and experimentally demonstrated. The laser topology is based on the parallel connection of fiber Bragg gratings (FBGs) using a coupler to realize switchability and tunability by adjusting the cavity losses and the center wavelengths of FBGs, respectively. The saturable absorber and the self-injection locking ensure the stable operation of the laser at SLM. Dual-wavelength with the power-instability of $\sim 0.7$ dB, the wavelength drift of ±0.08 nm, and a tuning range of 6.7 and 2.7 nm is obtained. Stable SLM operation with linewidths of <9.1 MHz analyzed by the self-homodyne method is obtained. The proposed configuration has ingenious and compact structure and reliable performance, and will have promising applications in the fields of multi-parameter detection in gas sensing or new wavelength-division-multiplexing (WDM) communication systems.