Scattering of surface plasmon polaritons at abrupt surface interfaces: Implications for nanoscale cavities

We have developed a rigorous mode matching approach for the analysis of surface wave scattering at nonuniform semi-infinite dielectric-metal interfaces. An analytical derivation of the coupling coefficients between surface waves allows an efficient scattering matrix formulation to describe general structures with multiple interfaces. Using this, we resolve issues of accuracy and convergence of related approaches in the literature. Studies of the reflection, transmission, and radiation of surface plasmons incident on both dielectric and metallic surface discontinuities show a correspondence with an effective Fresnel description. We also model a surface plasmon distributed Bragg reflector (DBR) capable of reflecting between 80% and 90% of incident surface plasmon power. Radiation mode scattering ultimately limits the DBR's reflection performance rather than the intrinsic absorption of the metal. Thus, alternative plasmonic geometries that suppress radiation modes, such as gap and channel structures, could be superior for the design of strongly reflective DBRs for integration in high-Q-factor nanoscale cavities. We anticipate that this method will be a valuable tool for the efficient and intuitive design of plasmonic devices based on structural nonuniformities.