Fano resonances in a single defect nanocavity coupled with a plasmonic waveguide

Two Fano resonances are theoretically predicted in a single defect nanocavity, consisting of a rectangular cavity with a small stub defect, side-coupled with a plasmonic waveguide. These two Fano resonances are found to originate from two different mechanisms. One is caused by the excitation of a high-order resonant mode in the rectangular cavity owing to the structural breaking, and the other is attributed to the inherent resonant mode in the small stub defect. The narrow high-order mode and inherent mode couple with the broad low-order resonant mode in the rectangular cavity, giving rise to two Fano resonances. Because of the different origins, these two Fano resonances exhibit quite different responses to the variations of the structural dimensions. This has important applications in highly sensitive and multiparameter sensing in the complicated environments.