Coupled-mode analysis for chiral fiber gratings with a core enclosed by a non-circular equiwidth curve

Polarization properties of chiral fiber gratings with the core enclosed by a non-circular equiwidth curve have been analyzed and examined numerically. Since the curve has multiple odd number degree of symmetries, the specific analysis is mainly based on the simplest triple-helix chiral fiber gratings and difference of properties caused by small geometric deformation. Results show that, only right-handed circularly polarized core modes couples with cladding modes. Besides, if the shape of the fiber core was closer to a circle, rather than a triangle with curved edges, both the shortest total power transfer length and the distance between the relevant resonant dips of the transmission spectrum would increase. Therefore, as a multiple-helix chiral fiber grating, it might have some potential applications, such as filters, polarizers, and sensors.