Controllable Laser Modes and Wavelength Selection in a Passively Q-switched Erbium-doped Fiber Laser

We report on a novel Q-switched all-fiber laser that allows direct oscillation of controllable transverse laser modes and switchable wavelengths using an intra-cavity based mode-selective coupler (MSC). The combination of a pair of fiber Bragg gratings and a MSC contributes to the wavelength and transverse-mode switching. Owing to the mode separation feature of the MSC and the dual-branch laser configuration, laser modes could be controlled with ease by tuning intra-cavity loss inside the dual-branch laser cavities. We observe a dual-wavelength Q-switched operation with simultaneous LP01 and LP11 modes output successfully. To the best of our knowledge, it is the first demonstration of intra-cavity MSC assisted all fiber laser emitting controllable modes and lasing wavelengths.