Physical mechanism of extraordinary electromagnetic transmission in dual-metallic grating structures

Very recently, in a short letter [Appl. Phys. Lett. 91, 111111 (2007)], we outlined some important results of electromagnetic transmission in dual-metallic grating structures composed of two identical single-metallic gratings with periodic subwavelength slit arrays. Here we describe and explain our theoretical study on the propagation property of the electromagnetic radiation in such structures in detail. The results manifest that the longitudinal interval and lateral displacement between the two single-metallic gratings strongly influence the electromagnetic transmission behavior in the dual-metallic grating structures. We discover some interesting phenomena such as the frequency shift and splitting of the high transmission peak, and the transmission suppression over a broad frequency region. We reveal that the coupling between the two single-metallic gratings is responsible for those phenomena. In addition, the case of oblique incidence is also explored.