Band structure of a two dimensional metallic photonic crystal and the   experimental observation of negative refraction in the microwave region
  In this paper we describe an application of the finite difference method to obtain the transverse magnetic photonic band gap diagram of a photonic crystal. The strategy of this method is to formulate the Maxwell equations in finite differences in order to write a computational code. We present experiments that confirm the validity of the calculations of the photonic band diagram as well as the refraction indix of such structure. All calculations were made for two dimensional metallic photonic crystal. 
R. A. Gutierrez-Arenas and D. Mendoza
physics.optics