Polarization gaps in spiral photonic crystals

We studied the optical properties of a dielectric photonic crystal structure with spirals arranged in a hexagonal lattice. The dielectric constant of the material was 9 and the filling ratio was 15.2%. We found that this kind of structure exhibits a significant polarization gap in the light that was incident along the axis of the spirals. The eigenmodes inside the polarization gap were predominantly right-hand (left-hand) polarized depending on the whether if the spirals are left-handed (right-handed). We calculated the transmission spectrum of a slab of such a structure and it matches well with the analysis of the eigenmodes.