Abstract
Multiple plasmonic Fano resonances are generally considered to require complex nanostructures, such as multilayer structure, to provide several dark modes that can couple with the bright mode. In this paper, we show the existence of multiple Fano resonances in single layer core-shell nanostructures where the multiple dark modes appear due to the geometrical symmetry breaking induced by axial offset of the core. Both dielectric-core-metal-shell (DCMS) and metal-core-dielectric-shell (MCDS) configurations have been studied. Compared to the MCDS structure, the DCMS configuration provides higher modulation depth. Analytical studies based on transformation optics and numerical simulations have been performed to investigate the role of geometrical and material parameters on the optical properties of the proposed nanostructures. Refractive index sensing with higher-order Fano resonances has also been described, providing opportunity for multiwavelength sensing with high figure of merit.
Highlights
Localized surface plasmons (LSPs) sustained by plasmonic nanostructures depend strongly on the geometry and size of the structures and the surrounding materials [1]
We show the existence of multiple Fano resonances in single layer core-shell nanostructures where the multiple dark modes appear due to the geometrical symmetry breaking induced by axial offset of the core
With analytical method based on transformation optics and numerical simulations, we show that for both configurations, introducing the symmetry breaking by the core displacement induces the appearance of higher-order multiple Fano resonances
Summary
Localized surface plasmons (LSPs) sustained by plasmonic nanostructures depend strongly on the geometry and size of the structures and the surrounding materials [1]. Various structures have been proposed to achieve Fano resonances, such as ring/disk nanocavities [7, 15,16,17], plasmonic metamaterials [18,19,20,21], modified nanodisks [22], single rod-shaped nanoantenna [23], nano-clusters [24, 25], heterodimer structures [26, 27], and nano-shells [28,29,30,31,32] Among those numerous designs, considerable attempts have been made to achieve multiple Fanoresonances [17, 21, 29, 30, 32], that enable the applications to be explored simultaneously at different frequencies. Since experimental realization of nanoshells with symmetry breaking has already been reported [37,38,39], we expect that the nonconcentric core-shell nanowires designed in this work can be implemented in active optical devices and applied in multifrequency molecular sensing and SERS
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