Investigation of the spectra of coupled polaritons on the periodically modulated metallic layer and the narrow regions of anomalous transparency

The paper deals with the theoretical investigation of plane, normally incident electromagnetic wave transmission through the flat metal film whose dielectric constant has small periodical sinusoidal modulation in one dimension parallel to the projection of the electric field onto the film surface. The dependencies of the film transmittancy on the parameters of the problem (frequency, modulation depth and absorption) are examined. It is shown that the film transmittancy increases considerably when the conditions for resonance interaction of an incident electromagnetic wave with surface plasmon polaritons (SPPs) are met. It is found that for small but finite absorption there are two frequencies in the vicinity of which the transmittancy can achieve the values of the order of unity due to resonances on symmetric and antisymmetric (relative to the mean plane) SPP modes. It is shown that for each value of absorption there exists a certain optimal modulation depth, which maximizes the resonance transparency.