Propagation of optical vortices in coiled weakly guiding optical fibers

The structure of the l = 1 modes of regularly coiled weakly guiding optical fibers with round cross section is determined. The l = 1 modes are shown to be represented by two right-and left-hand polarized stable optical vortices, as well as by TE and TM modes. The polarization corrections to the scalar propagation constant are found. The stability of an optical vortex transmitted along a coiled fiber is estimated. The parameters for optimal coiling at which the transmission of vortices along the fibers is the most stable with respect to fiber perturbations are determined.