Temporal coupled-mode theory for resonant apertures

We develop the coupled-mode theory for nanoscale resonant apertures. We show that the maximum transmission and absorption cross sections for subwavelength resonant apertures are only related to the wavelength of the incident light and the directivity of the aperture's radiation pattern. A general relation between the transmission cross section and the directivity is proven from the coupled-mode theory. As a specific example, we apply the theory to a nanoslit aperture in a metallic film and obtain excellent agreement with direct numerical simulations. (C) 2010 Optical Society of America