Nanomechanical modulation cavities of localized surface plasmon resonance with elastic whispering-gallery modes

Abstract

The dispersion of mechanical vibration limits nano-optomechanical modulation. In this work, we propose an optomechanical modulation exploiting elastic local resonances, also called whispering-gallery modes (WGMs). We find that our structure supports two quadripolar and two hexapolar elastic WGMs, which are nondispersive to avoid losses where the displacement field is localized on the gold nanodisks (AuNDs). We numerically demonstrate that the coupling between localized surface plasmon resonance (LSPR) and WGMs are relative both to the symmetry displacement of the elastic modes and to the strong isolation of phononic modes in the AuNDs. The amplitude of the modulation is evaluated by computing the wavelength shift of dipolar LSPR under different deformations by four WGMs. A detailed comparison between the four WGMs allows us to determine the ones with more efficient coupling. Furthermore, this simultaneous confinement gives a large acousto-plasmonic coupling that can be used to design a new mechanical sensor with the plasmonic response as a potential application and innovation toward new acousto-plasmonic devices.