52 research outputs found
Paired cut-wire arrays for enhanced transmission of transverse-electric fields through sub-wavelength slits in a thin metallic screen
It has recently been shown that the transmission of electromagnetic fields
through sub-wavelength slits (parallel to the electric field direction) in a
thin metallic screen can be greatly enhanced by covering one side of the screen
with a metallic cut-wire array laid on a dielectric layer. In this Letter, we
show that a richer phenomenology (which involves both electric- and
magnetic-type resonances) can be attained by pairing a second cut-wire array at
the other side of the screen. Via a full-wave comprehensive parametric study,
we illustrate the underlying mechanisms and explore the additional degrees of
freedom endowed, as well as their possible implications in the engineering of
enhanced transmission phenomena.Comment: 4 pages, 8 figures; slight corrections in Figs. 1, 2, and
Electromagnetic tunneling through a single-negative slab paired with a double-positive bi-layer
We show that resonant tunneling of electromagnetic fields can occur through a
three-layer structure composed of a single-negative (i.e., either
negative-permittivity or negative-permeability) slab paired with bi-layer made
of double-positive (i.e., positive permittivity and permeability) media. In
particular, one of the two double-positive media can be chosen arbitrarily
(even vacuum), while the other may exhibit extreme (either near-zero or very
high) permittivity/permeability values. Our results on this counterintuitive
tunneling phenomenon also demonstrate the possibility of synthesizing
double-positive slabs that effectively exhibit single-negative-like
wave-impedance properties within a moderately wide frequency range.Comment: 5 pages, 5 figures (minor revisions
A General Class of Metamaterial Transformation Slabs
In this paper, we apply transformation-based optics to the derivation of a
general class of transparent metamaterial slabs. By means of analytical and
numerical full-wave studies, we explore their image displacement/formation
capabilities, and establish intriguing connections with configurations already
known in the literature. Starting from these revisitations, we develop a number
of nontrivial extensions, and illustrate their possible applications to the
design of perfect radomes, anti-cloaking devices, and focusing devices based on
double-positive (possibly nonmagnetic) media. These designs show that such
anomalous features may be achieved without necessarily relying on
negative-index or strongly resonant metamaterials, suggesting more practical
venues for the realization of these devices.Comment: 25 pages, 13 figures; minor changes in the tex
Guided resonances in photonic quasicrystals
In this paper, we report on the first evidence of guided resonances (GRs) in
aperiodically-ordered photonic crystals, tied to the concept of "quasicrystals"
in solid-state physics. Via a full-wave numerical study of the transmittance
response and the modal structure of a photonic quasicrystal (PQC) slab based on
a representative aperiodic geometry (Ammann-Beenker octagonal tiling), we
demonstrate the possibility of exciting GR modes, and highlight similarities
and differences with the periodic case. In particular, we show that, as for the
periodic case, GRs arise from the coupling of the incident plane-wave with
degenerate modes of the PQC slab that exhibit a matching symmetry in the
spatial distribution, and can still be parameterized via a Fano-like model.
Besides the phenomenological implications, our results may provide new degrees
of freedom in the engineering of GRs, and pave the way for new developments and
applications.Comment: 12 pages, 8 figures, 1 table. Three figures added; Sec. 3.3
significantly expande
Experimental evidence of guided resonances in photonic crystals with aperiodically-ordered supercells
We report on the first experimental evidence of guided resonances (GRs) in
photonic crystal slabs based on aperiodically-ordered supercells. Using the
Ammann-Beenker (quasiperiodic, 8-fold symmetric) tiling geometry, we present
our study on the fabrication, experimental characterization, and full-wave
numerical simulation of two representative structures (with different filling
parameters) operating at near-infrared wavelengths (1300-1600 nm). Our results
show a fairly good agreement between measurements and numerical predictions,
and pave the way for the development of new strategies (based, e.g., on the
lattice symmetry breaking) for GR engineering.Comment: 10 pages, 5 figures (minor revisions
Transformation-optics generalization of tunnelling effects in bi-layers made of paired pseudo-epsilon-negative/mu-negative media
Transformation-media designed by standard transformation-optics (TO)
approaches, based on real-valued coordinate-mapping, cannot exhibit
single-negative (SNG) character unless such character is already possessed by
the domain that is being transformed. In this paper, we show that, for a given
field polarisation, pseudo-SNG transformation media can be obtained by
transforming a domain featuring double positive (or double-negative) character,
via complex analytic continuation of the coordinate transformation rules.
Moreover, we apply this concept to the TO-based interpretation of phenomena
analogous to the tunnelling effects observable in bi-layers made of
complementary epsilon-negative (ENG) and mu-negative (MNG) media, and explore
their possible TO-inspired extensions and generalizations.Comment: 13 pages, 1 table, 6 figures; minor changes in the title and tex
Guided resonances in photonic crystals with point-defected aperiodically-ordered supercells
In this paper, we study the excitation of guided resonances (GRs) in
photonic-crystal slabs based on point-defected aperiodically-ordered
supercells. With specific reference to perforated-slab structures and the
Ammann-Beenker octagonal lattice geometry, we carry out full-wave numerical
studies of the plane-wave responses and of the underlying modal structures,
which illustrate the representative effects induced by the introduction of
symmetry-preserving and symmetry-breaking defects. Our results demonstrate that
breaking the supercell mirror symmetries via the judicious introduction of
point-defects enables for the excitation of otherwise uncoupled GRs, with
control on the symmetry properties of their field distributions, thereby
constituting an attractive alternative to those GR-engineering approaches based
on the asymmetrization of the hole shape. In this framework,
aperiodically-ordered supercells seem to be inherently suited, in view of the
variety of inequivalent defect sites that they can offer.Comment: 13 pages, 12 figures, 1 table. Slight change in the title; major
changes in the text and figure
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