Guided modes supported by plasmonic films with a periodic arrangement of subwavelength slits

We calculate the guided band diagram of a metallic film with a one-dimensional periodic arrangement of cut-through subwavelength slits. We find that this system supports two distinct types of guided modes propagating in a direction perpendicular to the slits when the metal obeys a plasmonic dispersion model. The first type is a well-known surface mode. The second type results from the presence of a subwavelength electromagnetic resonance inside the slits and closely resembles waveguide modes in a dielectric slab. We refer to them as effective dielectric slab modes. We show how the behavior of both modes is affected by film thickness and surface properties. (c) 2006 American Institute of Physics.