Quadruple-Dyadic Spectral Green's Functions of Current Sources in Planar Layered Media: Application to Plasmonic Layer-Structures

In this paper a generalized formulation for the spectral domain Green's functions of unit current sources embedded within a multilayer stack is presented. The current source can be either electric or magnetic. It can be oriented either parallel to the layers or perpendicular to them. The electric and magnetic fields due to these generalized sources are calculated. The proposed technique utilizes inward and outward recurrence processes in order to solve for the desired quadruple-dyadic Green's functions. It requires the calculation of 6 spectral coefficients only, from which all types of spectral Green's functions can be calculated. The proposed formulation is written such that the electromagnetic fields are directly obtained in terms of the current sources rather than the vector and scalar potentials with no explicit analogy with transmission lines. The dependencies on the
z
-coordinates of the source and field points are expressed explicitly, which is important for Volume Integral Equation (VIE) formulation. The proposed generalized formulation is applied on a number of plasmonic layer structures such as Insulator/Metal/Insulator (IMI), Metal/Insulator/Metal (MIM), and five-layer plasmonic/dielectric layer structure. The poles of the spectral domain Green's functions are linked to the Surface Plasmon Polaritons (SPPs), i.e., surface wave modes, associated with the source-free layer structure. The spectral Green's functions calculated using the proposed generalized technique are also used by an in-house Method of Moments (MoM) solver. The results of this solver are compared with those obtained by a full-wave commercial software.