Metal-dielectric-metal surface plasmon-polariton resonators

A theoretical study of standing-wave resonances of surface plasmon polaritons (SPPs) in finite-length metal-dielectric-metal cavities is presented. A Fabry-P\'erot model is constructed to describe the cavity resonances, and the associated optical parameters are calculated analytically. One key parameter is the phase acquired by resonating SPPs upon reflection from cavity end faces. This phase pickup is associated with the near-field energy storage at these end faces, and the imaginary part of the reflection coefficient is shown to be approximately proportional to the stored energy. Using the Fabry-P\'erot model, we also calculate the transmission cross section, peak position, as well as the $Q$ factor of the cavity, and we find good agreement with full-field numerical simulations for a wide range of wavelengths and device dimensions.