Surface plasmon modes and their interactions in multilayer thin-film structures

Abstract

The propagation of surface plasmons in thin films is important for a number of technologies and has found applications in chemical and biological sensing. There is growing interest in the use of surface plasmons coupled with optical systems for high density photonic devices. While the analysis of the properties of surface plasmons at a metal-dielectric interface is straightforward, it becomes increasingly more difficult as the number of surfaces is increased, as in a multi-layer thin film structure. In this paper we discuss recent developments in mathematical methods for studying the properties of surface plasmons in multi-layer thin film structures of the metal-insulator-metal (MIM) type. The films may consist of a large number of layers creating MIMIM... structures that determine the allowed modes of the surface plasmons. The mathematical formulation is based on a matrix method that yields the eigenvalues (dispersion relation) and the eigenfunctions (mode profiles) associated with the surface plasmons. The method is used to analyze modes in a number of structures. In particular it is shown that modes in structures that contain an optically resonant film can have dispersion curves that cross one another and that changing the resonances in the film can lead to switching of the surface plasmon modes.