39 research outputs found
Switching from visibility to invisibility via Fano resonances: theory and experiment
Subwavelength structures demonstrate many unusual optical properties which
can be employed for engineering functional metadevices, as well as scattering
of light and invisibility cloaking. Here we demonstrate that the suppression of
light scattering for any direction of observation can be achieved for an
uniform dielectric object with high refractive index, in a sharp contrast to
the cloaking with multilayered plasmonic structures suggested previously. Our
finding is based on the novel physics of cascades of Fano resonances observed
in the Mie scattering from a homogeneous dielectric rod. We observe this effect
experimentally at microwaves by employing high temperature-dependent dielectric
permittivity of a glass cylinder with heated water. Our results open a new
avenue in analyzing the optical response of hight-index dielectric
nanoparticles and the physics of cloaking.Comment: 8 pages, 4 figure
Interplay of magnetic responses in all-dielectric oligomers to realize magnetic Fano resonances
We study the interplay between collective and individual optically-induced
magnetic responses in quadrumers made of identical dielectric nanoparticles.
Unlike their plasmonic counterparts, all-dielectric nanoparticle clusters are
shown to exhibit multiple dimensions of resonant magnetic responses that can be
employed for the realization of anomalous scattering signatures. We focus our
analysis on symmetric quadrumers made from silicon nanoparticles and verify our
theoretical results in proof-of-concept radio frequency experiments
demonstrating the existence of a novel type of magnetic Fano resonance in
nanophotonics.Comment: 20 pages, 7 figure
Phase diagram for the transition from photonic crystals to dielectric metamaterials
Photonic crystals and metamaterials represent two seemingly different classes
of artificial electromagnetic media but often they are composed of similar
structural elements arranged in periodic lattices. The important question is
how to distinguish these two types of periodic photonic structures when their
parameters, such as dielectric permittivity and lattice spacing, vary
continuously. Here, we discuss transitions between photonic crystals and
all-dielectric metamaterials and introduce the concept of a phase diagram and
an order parameter for such structured materials, based on the physics of Mie
and Bragg resonances. We show that a periodic photonic structure transforms
into a metamaterial when the Mie gap opens up below the lowest Bragg bandgap
where the homogenization approach can be justified and the effective
permeability becomes negative. Our theoretical approach is confirmed by
detailed microwave experiments for a metacrystal composed of a square lattice
of glass tubes filled with heated water. This analysis yields deep insight into
the properties of periodic photonic structures, and it also provides a useful
tool for designing different classes of electromagnetic materials in a broad
range of parameters.Comment: 7 pages, 6 figure
Broadband isotropic μ-near-zero metamaterials
Natural diamagnetism, while being a common phenomenon, is limited to permeability values close
to unity. Artificial diamagnetics, to the contrary, can be engineered to provide much lower values
and may even possess an effective permeability close to zero. In this letter, we provide an
experimental confirmation of the possibility to obtain extremely low permeability values by
manufacturing an isotropic metamaterial composed of conducting cubes. We show that the
practical assembly is quite sensitive to fabrication tolerances and demonstrate that permeability of
about μ=0.15 is realisable.This work was supported by the Ministry
of Education and Science of Russian Federation (Project
11.G34.31.0020), Dynasty Foundation (Russia), grant of the
President of Russian Federation, and by the Australian
Research Council (CUDOS Centre of Excellence
CE110001018)