Polarization properties of chiral fiber gratings

Recent experiments (Kopp et al 2007 J. Opt. Soc. Am. B 24 A48) have demonstrated that the polarization sensitivity of chiral fiber gratings depends strongly on the grating symmetry: double-helix fibers are polarization sensitive while single-helix fibers are not. A coupled-mode perturbation theory is developed and used to explain the polarization properties of chiral fiber gratings. Features of the transmission spectrum such as multiple dips in the spectrum and circular dichroism are also derived and attributed to chiral Bragg scattering of the core modes into the cladding modes of the fiber.