Hybridization and the origin of Fano resonances in symmetric nanoparticle trimers

Abstract

We study the light scattering by plasmonic and dielectric symmetric trimers to investigate the existence of polarization-independent Fano resonances. Plasmonic hybridization theory is revealed to hide simple physics, and we instead provide a simplified model for hybridization to derive a plasmonic trimer's eigenmodes analytically. This approach is demonstrated to accurately recreate full wave simulations of plasmonic trimers and their Fano resonances. We are subsequently able to deduce the grounds for modal interference in plasmonic trimers and the related formation of Fano resonances. However, by taking advantage of the generality of our simplified hybridization approach, we are also able to investigate the eigenmodes of all-dielectric trimers. We show that bianisotropic coupling channels between high-index dielectric nanoparticles are able to increase the capacity for Fano resonances, even at normal incidence. We finally provide the first experimental measurements of sharp, polarization-independent Fano resonances from a symmetric all-dielectric trimer, with very good agreement to the predicted response from our simplified hybridization theory.

Asymmetric backscattering from the hybrid magneto-electric meta particle

“…One of the fundamental properties of Maxwell's equations is that they are frequency scalablethis means that scattering from meta-atoms designed for the optical frequencies would be analogous to scattering from a similar meta-atom designed for radio frequencies (RF), provided that the material parameters and are the same [29]. This scalability enables emulation of optical metamaterials, which are often difficult to fabricate due to their small dimensions, with the relatively easily manufacturable metamaterials in the RF range [30], [31].…”

Cooperative eigenmodes and scattering in one-dimensional atomic arrays

“…As with the Fano resonance, the sign of the interference changes as the driving goes through resonance with the narrow mode, resulting in an asymmetric interference lineshape. Fano-like interference lineshapes have been predicted and observed in a number of coupled dipole systems [23,26,28,[77][78][79].…”

All-Dielectric Nanophotonic Structures: Exploring the Magnetic Component of Light

“…The number of eigenmodes of this system is much higher, because of both the additional magnetic dipoles and because electric-magnetic dipole coupling (cf. Equation 10.9) allows each dipole to be polarized parallel to the propagation direction [54]. The first consequence of this increased eigenmode count is that there are many more signatures of interference phenomena occurring across the extinction spectra.…”

“…An exceptional point refers to a point degeneracy of two or more eigenvalues when their eigenmodes simultaneously become linearly dependent, subsequently corresponding to a reduction in the dimension of the span of eigenmodes [55][56][57]. Exceptional points can exist even in simple plasmonic and dielectric oligomer systems at complex frequencies [54], but can generally be expected to occur more regularly when there are more interacting eigenmodes. For the discussion here, we need to recognize that the excitation magnitudes of coalescing eigenmodes can diverge in the vicinity of an exceptional point, given a component of the driving field is gradually becoming orthogonal to the eigenmodes that span it.…”

“…Assuming a normally-incident plane wave, the number of excitable eigenmodes in these rotationally-symmetric plasmonic oligomers is relatively contained: two degenerate pairs of eigenmodes for each ring of nanoparticles and one further pair if there is central nanoparticle [22]. On the other hand, the coupling between electric and magnetic dipoles in dielectric oligomers removes such eigenmode restrictions, making the number of excitable eigenmodes increase with the number of nanoparticles in each ring [54]. This means that even simple arrangements of dielectric nanoparticles can be used to achieve the behavior of more complicated plasmonic oligomers, an example of which will be investigated in the next section.…”