Tunability and linewidth sharpening of plasmon resonances on a periodic gold nanowire array coupled to a thin textured silver film

We theoretically study the plasmon mode spectrum of a multilayer structure consisting of a periodic gold nanowire array and a spatially separated thin silver film with periodic slits. Results show that the plasmon mode spectrum of the multilayer structure depends sensitively on the relative lateral displacement of the Au nanowire array with respect to the textured silver film. This is due to the interaction between the localized surface plasmon (LSP) of the nanowire array and the plasmon modes, including the horizontal LSP and the antisymmetric short-range surface plasmon polariton (SPP), of the textured thin silver film. The strong coupling between the LSP and the antisymmetric short-range SPP results in a redshifted plasmon resonance with a significantly narrow linewidth and a large electromagnetic field enhancement. Moreover, the lateral displacement also has a great influence on the spacer layer controlled dipole-surface interaction. Therefore, this relative lateral displacement provides an efficient way to tune the optical properties of the multilayer structure, and this kind of highly tunable nanostructure can be used as a tunable plasmonic filter or a substrate for LSPs sensor.