Destruction of a polaritonic gap in a 2D photonic crystal

In a photonic crystal, an ionic material causes a wide polaritonic gap in the infrared region, induced by lattice resonances. A 2D square photonic crystal consisting of BeO cylinders in a dielectric matrix is studied by transfer matrix photonic band structure calculations. In particular it is shown under what conditions - in terms of the packing fraction of the cylinders, and the dielectric function of the matrix - the polaritonic gap can be destroyed.