Enhanced photonic band gaps of periodic dielectric structures composed of double cylindrical rods

On the basis of Maradudin and McGurn's model we investigate the spectral pr operties of a two-dimensional photonic crystal, consisting of cylindrical r ods disposed periodically throughout a dielectric matrix (the crystal is li mited by two surfaces perpendicular to the axes of the rods). The model is supplemented by a new structural element in the form of dielectric rods (al so cylindrical in shape) disposed coaxially within the original rods. The c enters of both kinds of rods overlap forming a two-dimensional rectangular lattice in the plane parallel to the surface. Thus, the object of our study is a Maradudin-McGurn's model in which the individual rods are replaced by coaxial double rods. For this modified model we search for the optimal set of structural parameter values for which the forbidden energy gaps become greatest, giving especial attention to the role played by the additional in ner rods in the emergence of gaps. We arrive at the conclusion that the con dition for the opening of absolutely forbidden gaps become more favourable in a photonic crystal with double rods compared with those required in a cr ystal with simple rods.