Polarization dependent Fano resonance in a metallic triangle embedded in split ring plasmonic nanostructures

The extinction properties of a plasmonic nanocavity consisting of a regular triangle embedded in a split ring (RTSR) plasmonic nanostructure have been investigated. Due to symmetry breaking of the RTSR cavity, we find that the extinction properties of the RTSR cavity are highly sensitive to the polarization of the incident light, resulting in strong Fano resonances. The Fano resonances originate from strong coupling between the regular triangle and the split ring. It is found that the size and relative orientation of the regular triangle are crucial parameters for the Fano resonance since these parameters finely control the strength of the electromagnetic coupling and the effective capacitance of the metallic gap region. By using combinations of different symmetrical nanostructures we can actively modulate the Fano resonance spectra in a polarization dependent manner. Calculation results show that bulk refractive index sensitivities exceeding 800 nm/RIU, with a figure of merit exceeding 6.8 in the near-infrared, are obtained with the RTSR cavity. These properties give the RTSR cavity potential applications in plasmonic Fano switches and sensing.