Fano approximation for coupled modes in metal-dielectric multilayer structures

Abstract

We study the response of coupled modes in metal-dielectric multilayer planar structures consisting of a metal layer attached to a high-index waveguide by a low-index spacer layer. The structure supports excitation and coupling of a surface plasmon polariton mode and a waveguide mode. A coupled-mode model is developed to analyse the field transfer processes and describe the appearance of Fano resonances as a result of the modes interaction. It is demonstrated that the response of the plasmonic mode can be well fitted to a Fano function that allows extraction of width, height, sensitivity, and field enhancement.