A novel algorithm for analysis of surface plasmon polaritons in metallic thin films

C. Trampel, G. Kobidze, B. Shanker, and D.P. Nyquist

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Electromagnetic scattering from periodic objects is of particular interest because they support waves bound to the surface of the structure. Specifically, dielectrics with negative real permittivity support charge density oscillations known as surface plasmons. The coupling between a surface wave and charge density oscillation is the so-called surface plasmon polariton. Research into nano-plasmon optics is growing into a rich research field, with far reaching implications. The dispersion relation for SPPs has been derived for a periodic array of scatterers at the interface between two infinite media, and the resulting dispersion curves show strong band gaps. Even more interesting optical properties of SPPs have been observed experimentally. Metal films perforated by periodically distributed holes exhibit stronger transmission than that predicted by geometrical optics. These transmission peaks occur at the same frequencies as SPP modes. Surface plasmon polaritons excited on both interfaces funnel energy through the film, resulting in enhance transmission. Numerical modeling of perforated metal structures presents several computational challenges. Researchers have resorted to both volume and surface integral equations to model these effects. However, since the holes occupy only 5% of the area of the film, and the material itself has a large negative real permittivity, the discretization has to be sufficiently dense to capture the wave physics. In this paper, we present an alternative method that is considerably more efficient and requires only the region inside the hole to be meshed.

The paper proceeds as follows. In Section 2 the integral equation formulation of the scattering problem is presented. Section 3 describes the periodic Green’s function for a layered medium. The method of moments scheme is detailed in Section 4. Some preliminary results are presented in Section 5 as are the paper’s conclusions.