Dark to Bright Mode Conversion on Dipolar Nanoantennas: A Symmetry-Breaking Approach

Abstract

The excitation of plasmonic dark modes via a radiative channel is a phenomenon strongly hindered in the subwavelength regime. Recently, for achieving this purpose it has been proposed to exploit near-field interactions between radiating (bright) modes and lossless dark modes. However, this approach unveils challenging difficulties related to the excitation of dark modes through the near-field coupling with a bright mode. Here, it is experimentally and numerically shown how symmetry breaking applied to a nanoantenna dimer can conversely induce the excitation of plasmonic resonances, which play a key role for the dark modes' activation in more complex nanoassemblies. On the basis of this study, a Tshaped nanoantenna trimer has been introduced as an elemental unit for the energy transfer between bright and dark modes in plasmonic nanostructures. Finally, we implemented an analytical perturbative model to further investigate the plasmonic hybridization of subwavelength systems.

Dark and bright modes manipulation for plasmon-triggered photonic devices

“…In this condition, we can observe how the LSPs associated to the aligned dimer sub-system are exclusively triggered by near-field channel. For symmetry reasons, the mode sustained by the aligned dimer is dark 19 . …”

“…By gradually increasing θ, the extinction efficiency inside the dip rises becoming comparable with the bonding and anti-bonding resonance peaks. In θ = 45° condition we are exciting the bright modes sustained by the L-shape dimer sub-elements 19,20 and the aligned nanoantenna dark mode is completely suppressed. In this analysis, the high polarization sensistivity and spectral selectivity of T-shape trimer clearly emerges.…”

“…In fact dark modes, due to their weak coupling to free radiation, present narrow band spectral responses [14][15][16][17][18] . One of the simplest plasmonic systems which can sustain dark oscillations is the aligned nanoantenna dimer 19 . This elemental nanoassembly presents two low order hybridized modes: (i) the low energy (bonding) mode is characterized by the in-phase oscillation of the localized surface plasmons (LSPs) associated to each nanoantenna arm, and (ii) the high energy (anti-bonding) mode is determined by the mutually out-of-phase oscillation of LSPs.…”

Generation of High-Order Resonance Modes in Visible and Near-Infrared Range from Square Ring-Disk System

“…Noble metal nanostructures have been attracting more and more attention due to the development of the theory and application of surface plasmon resonance (SPR) [1][2][3][4]. Numerical simulation, which efficiently combines theoretical and experimental study, plays a very important role in the study of plasmonics.…”

Coil-type Fano Resonances: a Plasmonic Approach to Magnetic Sub-diffraction Confinement

“…The samples have been characterized via optical transmission spectroscopy in far-field (normal incidence condition), reporting the associated extinction efficiency spectra in Figure 2(b). By exploiting the morphological symmetry breaking [3,12] associated to the upper nanodisk, we can promote an intense out-of-phase oscillation of localized surface plasmons (LSPs) inside nanodisk trimers. In this regard, we can compare the charge current density distribution in the case of D = 160 nm ( Fig.…”