Generation of an azimuthally polarized beam with a metallic ring core fiber

A fiber with a thin-metallic layer introduced between the central core and the cladding is proposed to lift the near-degeneracy of the modes TE01, TM01, and HE21. It can be used to obtain the pure mode TE01 as both the active and passive fibers. In the case of the active fiber, the fiber with the appropriate rare earth doping profile in the central core is presented as the gain medium of a fiber laser. The numerical results show that the pure mode TE01 (99.99%) can be obtained. In the case of the passive fiber, Gaussian light beams with suitable shift distance from the center core are coupled into the fiber. The results indicate that only the mode TE01 remains with the increasing propagation distance.