“…A stable and wavelength-selectable erbium-doped fiber (EDF) ring laser is an attractive light source for applications such as optical fiber sensing, optical testing, microwave photonics, wavelength-division-multiplexing (WDM) transmission, and optical instrument testing [1][2][3][4]. Generally, in order to accomplish the wavelength lasing and tuning, the fiber Fabry-Perot tunable filter (FP-TF), tunable bandpass filter (TBF), and variable fiber Bragg grating (FBG) have been proposed and utilized inside the fiber-loop cavity [5][6][7]. Due to the modehopping and homogeneous broadening of EDF, it would result in the unstable and densely multi-longitudinal-mode (MLM) wavelength output [8].…”