Multiple Fano Resonances In Metal Nanoring Cavity Dimers

Over the past decade, the research related to the surface plasmonpolaritons(SSPs) of metallic nanostructures has drawn a lot of attention. Theoptical properties were originated from localized surface plasmon resonances.Localized surface plasmon resonances (LSPRs) in metallic nanostructures are ofseveral characteristics,such as strong nearfield enhancement, sensitive toenvironmental influences, can break through the diffraction limit and so on, thusleading it to a wide application on biosensing, SERS, subluminal propagation,nano antenna, non-linear enhancement and so on. However, radiative dampingdramatically increases as the particle size increases, and we often encountersituations where the line width is broad and the sensing performance is poor.Fano resonance caused by destructive interference between subradiantdark modes and superradiant bright modes. The excitation of dark modes cansuppress radiative damping effectively, resulting in a narrow line width and strong near field enhancement, and the sensing performance characterized byfigure of merit (FOM) can be significantly improved. When a system haveseveral subradiant dark modes,the interference of subradiant dark modes andsuperradiant bright modes can lead to the fomation of the Multiple Fanoresonances. Multiple Fano resonances are very suitable for multi-wavelengthbiosensing because they can simultaneously modify the plasmon line at severalspectral positions.This study proposes that surface plasmon interaction between dark modesis a favorable method to generate multiple Fano resonances. According to theplasmon hybridization theory, the interaction between dark modes can lead tothe formation of a subradiant bonding and a subradiant antibonding combination.The destructive interference between both hybridization subradiant dark modesand superradiant bright mode can lead to the appearance of double Fanoresonances in the spectra.In this paper, it demonstrates that a concentric ring/ring cavity dimer.Research has shown that without breaking system symmetry, the interactionbetween nano rings can directly excite the quadrupole resonance mode, and theinteractions render bonding subradiant hybridized mode, thus leading to thefomation of the Fano resonance in spectra. The corresponding antibondingquadrupolar ring mode is excited in a symmetry breaking nonconcentric cavitydimer, and double Fano resonances appear in the spectra.