Mixed Electric/Magnetic Fano Resonances in a Combined Square-Shaped Split Ring With an Internal Square Nanoantenna Nanocavities

Generally, the plasmonic Fano resonances can be divided into two types: the electric and the magnetic Fano resonance. Compared to pure electric or magnetic multiple Fano resonances, the mixed electric/magnetic multiple Fano resonances provide more flexibility for their application in multiwavelength surface enhanced Raman scattering and biosensing. Whereas, the dramatic difference between the two Fano resonances makes it difficult to realize magnetic and electric Fano resonances together in the same structure. In this paper, magnetic-octupole mode based Fano resonance and electric-quadrupole mode based Fano resonances in optical frequency were together achieved in a combined square-shaped split-ring resonator with an internal square nanoantenna nanocavities. The two Fano resonances are switchable by adjusting the polarization of the incident light. The lineshape modulated by the geometry and the environment of the two Fano resonances was investigated. Both the Fano resonances show high sensitivity to the environment. This study reveals a new multiple Fano resonance constitution and the proposed structure, which are expected with benefit application in multiwavelength polarization modulated chemistry and biological sensing.