Fano
resonances in plasmonics have received widespread attention for their
distinctly narrow asymmetric line shapes. A variety of configurations
have been considered, either requiring complex metallic nanostructures
or being extremely faint if originated in simple single nanoparticles.
Here we report on the emergence of high-contrast, strongly asymmetric
Fano line shapes in the light scattered from semiconductor nanorods.
Numerical calculations are carried out for the scattering cross sections
of finite semiconducting nanorods, with dimensions such that the lowest-order
(transverse) Mie resonances coexist with the lowest-order guided modes.
Such intense narrow Fano resonances are strongly/weakly asymmetric
in TE/TM polarization and overlap with the Mie-like background. A
physical interpretation is presented stemming from the (strong or
weak) interference of the far-field angular patterns of Mie resonances
(indeed, of both magnetic and dielectric dipole character) with narrow
Fabry–Perot (guided mode) resonances, the latter calculated
through a 1D line current model. A quasi-analytical expression is
developed for the scattering cross sections that reproduce fairly
well the Fano numerical line shapes, along with a generalized Fano
formula, with fitting factors confirming their high asymmetry and
contrast. These high-contrast, strongly asymmetric Fano resonances
herein obtained could be potentially exploited in nanophotonics and
sensing in the visible and near-IR, eased by simplified fabrication
requirements of shape (nanorod) and material (semiconductor).
A two-dimensional monolayer multi-scaled polyaniline inverse opal film is fabricated and exhibits efficient polarization filtering, which separates s- and p-polarized light for polarization sensing and imaging.
We consider the design of magnetic mirrors that consist of a layer of two-dimensional high-refractive-index dielectric particles. The central idea is to search for conditions for which the electric field of the light backscattered by a single particle has a zero phase difference with respect to the incident field. Employing physical arguments, we conclude that this can occur when the electric dipolar contribution vanishes. Optimizing the form of the cross section, we find a situation in which the vanishing of the dipolar contribution coincides with an in-phase condition for the magnetic dipole and the electric quadrupole contributions. The resulting scattering pattern of the particle resembles that of an electric dipole, with the difference that the forward and backscattered electric fields have opposite signs. Based on these results, we design a metasurface reflector that behaves as a magnetic mirror at a specific wavelength within a wideband spectral response. Subsequently, we extend the results to the design of supported structures where a magnetic mirror condition at a single wavelength is similarly found.
We demonstrate polarization-switching in conducting, electrochromic photonic-crystal films. These ordered, multi-scale structures offer numerous opportunities for inexpensive, large-area, active metasurfaces and fabrication over flexible and non-flat substrates.
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