An all-fiber Raman laser for cylindrical vector beam generation

We demonstrate a compact Raman all-fiber oscillator for cylindrical vector beam generation. The laser is based on a strongly guiding passive fiber with two fiber Bragg gratings inscribed in it, which separates the different transverse modes in wavelength. Additionally, the impact of core ellipticity in strongly guiding fibers for the generation of cylindrical vector beams is theoretically analyzed. In this work, the elliptical core is compensated by introducing stress. Thereby, an azimuthally polarized beam with an output power of 480 mW and a radially polarized beam with an output power of 400 mW are generated, limited only by the onset of nonlinear effects inside the Raman fiber oscillator. Switching between these two cylindrical vector beams is possible by rotating the polarization of the pump. The presented concept is well suited for all-fiber microscopic applications.