Double Fano resonance with externally driven subradiant mode

In this study, we observe that a dark mode is not necessarily prerequisite for an asymmetric Fano resonance to take place in plasmonic structures. The characteristic asymmetry feature of Fano resonance is retained in a plasmonic structure when both superradiant and subradiant oscillators are externally driven. Double Fano resonances are experimentally and theoretically observed where a common subradiant driven oscillator is coupled with two superradiant oscillators. As a classical analogue of a four-level tripod atomic system, the extinction spectrum of the composite metamaterial exhibits a coherent effect based on double Fano resonances. Transfer of the absorbed power between two orthogonal superradiant oscillators is shown to be mediated by the common subradiant oscillator.