Switchable single-longitudinal-mode narrow linewidth fiber laser with cylindrical vector beam output

Abstract

We experimentally demonstrated a switchable single-longitudinal-mode (SLM) narrow linewidth fiber laser with cylindrical vector beam (CVB) output. A mode selective filter is composed of a fiber Bragg grating and a mechanical long period fiber grating (LPFG), and it is used to realize the mode switch and wavelength switch. The compound ring cavity structure is composed of a main ring cavity and two passive subring cavities (SCs) so that the SLM operation is achieved. By controlling the polarization state of the light in the laser cavity and the pressure applied to the mechanical LPFG, both the radially and azimuthally polarized CVBs are obtained at 1543.35nm and 1544.38nm. Meanwhile, the signal-to-noise ratio is higher than 60dB. The 20dB linewidth of the proposed fiber laser for each wavelength is approximately 5.7kHz and 6.8kHz.