Focusing properties of a photonic crystal slab with negative refraction

A layered Korringa-Kohn-Rostoker method is exploited to study the subwavelength imaging through a slab of rods-in-air photonic crystal. Both the intensity and phase spectra of transmission are investigated. The high transmission of evanescent waves arises due to the excitation of some slab-guided bound modes and the high coupling between the incident evanescent field and some bulk-guided Bloch modes. Through a study of the phase spectrum of transmission, it is shown that the self-collimation effect occurs at smaller incident angles whereas the negative refraction effect occurs at relatively larger incident angles. The existence of imaging aberrations is also explained with the phase spectrum. The focusing properties of the photonic crystal slab are mainly due to the negative-refraction effect for large incident angles, rather than the self-collimation effect.