Multi-wavelength and transversely mode-switchable fiber laser based on ring-core fiber Bragg grating

A multi-wavelength and transversely mode-switchable fiber laser based on a ring-core fiber Bragg grating (RCFBG) is proposed. Two RCFBGs with high and low reflectivity are inscribed using a femtosecond laser and the phase mask scanning technique, serving as the mirrors in an all-fiber laser linear resonator. Leveraging the polarization dependence of the RCFBG through side exposure, we can readily achieve switchable single-wavelength, dual-wavelength, or triple-wavelength laser outputs by adjusting the polarization controller (PC) inside the resonator. Additionally, three distinct modes, namely, cylindrical vector beam (CVB), fundamental and mixed modes, are successfully obtained in single-wavelength laser operation. Azimuthally or radially polarized lasers can be realized by tuning two PCs inside and outside the resonator while operating in CVB mode. This innovative multi-wavelength and transversely mode-switchable fiber laser based on RCFBGs holds significant potential for applications in wavelength division multiplexing and mode division multiplexing systems.