Strong Coupling between Propagating and Localized Surface Plasmons in Plasmonic Cavities

Au/GaAs/Au plasmonic cavities with a periodic hole array perforated in the top Au layer are studied. Propagating surface plasmons (PSPs) and localized surface plasmons (LSPs) associated with the rectangle hole shapes are found to interact and highly hybridize in the cavity structure, which eventually determines the resonance properties of the cavities. An anticrossing of resonance frequencies in the reflection spectra is observed when the frequency of PSPs approaches that of LSPs, demonstrating the strong coupling between SPPs and LSPs in the tri-layer plasmonic cavities. This work may provide hints to the plasmonic cavity design for light-harvesting optoelectronic applications.