| Plasmonic structures, with periodic arrays of thin PMMA (Poly Methyl Methacrylate) ridges on metal substrates have been shown experimentally to overcome the diffraction limit. Here we present a theoretical description of this phenomenon. We use Mode Matching Method to analyze the dynamics of the electromagnetic waves in the periodic systems, taking into account the extended 2D-geometry and the finite thickness of the PMMA ridges. Specifically, we focus on the behavior of the plasmonic mode and its non-trivial coupling to the free space waves and to the other guided modes of the system. The eigenstates of the periodic system dominated by the surface waves are identified and their dispersion is analyzed via generalization of the mode-matching formalism and Bloch-periodic approach. An analytical approximation, adequately describing the behavior of the system is derived and is used to explain the suppression of diffraction in the system. |
