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

Abstract A multi-wavelength and transversely mode-switchable fiber laser based on ring-core fiber Bragg grating (RCFBG) is proposed. Two RCFBGs with high and low reflectivities are inscribed by femtosecond laser and phase mask scanning technique, serving as the mirrors of an all-fiber laser linear resonator. Leveraging the polarization dependence of RCFBG through side exposure, we can readily achieve single-wavelength, dual-wavelength, or triple-wavelength switchable laser outputs by adjusting the polarization controller (PC) inside the resonator. Additionally, three distinct modes—namely cylindrical vector beam (CVB), fundamental and mixed modes—have been 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.