Some study of 2D photonic crystals of negative refraction for subwavelength focusing

A slab of "left-handed material" (LHM) with simultaneously negative permittivity and permeability has the amazing property of subwavelength focusing, i.e., focusing the propagating components and restoring the evanescent components of the field of a point source placed in front of the slab. One of the most important applications of subwavelength focusing is the realization of an optical lens that may overcome the diffraction limit. Subwavelength focusing can also be achieved by a slab of photonic crystal (PhC) with negative refraction. We study the mechanism of the amplification of evanescent waves in these special photonic crystals and the contribution of various field components to the subwavelength focusing with the effective layer-KKR (Korringa-Kohn-Rostoker) method (Ohtaka, K. et al., 1998; He, S. et al., 2004) and the scattering matrix method (Whittaker, D.M. and Culshaw, I.S., 1999). A relationship between the band structure and the transfer spectrum function is established and the role of negative refraction for the amplification of evanescent waves in a photonic crystal is examined. The impact of loss and surface termination to subwavelength focusing is also studied. The subwavelength focusing performance of these PhC slabs is compared with that of a LHM slab.