PLANAR DEFECTS IN PHOTONIC CRYSTALS

We establish the existence of an absolute frequency gap of the electro magnetic field in photonic crystals with tetragonal symmetry, and exam ine the dependence of the gap on the geometry of the structure. We cal culate the transmittance through a slab of finite thickness of the mat erial, and show that planar defects in the slab produce interface stat es of the electromagnetic field, at frequencies within the photonic ga p, manifested by sharp resonances in the transmittance of these system s