Metal-insulator-metal thin film stack: flux enhancement due to coupling of surface plasmon polariton with wave guide modes

Abstract

Abstract A theoretical study is presented of the dispersion of surface plasmon polariton (SPP) and wave guide (WG) modes of a metal-insulator-metal (MIM) thin film stack. We study the dispersion of the reflectance and of the transmitted flux, originating from a local excitation source, of an asymmetric MIM air-Au-SiO2-Au-Ti-glass material system in the infrared and visible spectral region for a wide range of SiO2 and gold thicknesses, d S i O 2 and d A u . In comparison to reference stacks of air-Au-glass or air-SiO2-glass, between 1.4 and 2.0 eV, the transmitted flux intensity is enhanced 12 or 25 times, in the emission direction of the in-plane wave vector k ρ / k 0 ≈ 1.05 and for a thickness of d S i O 2 ∈ [300–700] nm, respectively. This enhancement is attributed to the coupling, through the avoided crossings, between the SPP a i r and WG modes. As the fields of the SPP a i r and WG modes are located in different regions of space the enhancement is nearly independent of the number of nodes in the WG mode. In summary we have identified sets of parameters giving rise to the observables enhancement. Therefore the present MIM thin film stack is a simple and a versatile system for the use in applications.