95 research outputs found
All-dielectric resonant metasurfaces with a strong toroidal response
We demonstrate how to create all-dielectric metasurfaces with a strong
toroidal response by arranging two types of nanodisks into asymmetric quadrumer
clusters. We demonstrate that a strong axial toroidal response of the
metasurface is related to conditions of the trapped (dark) mode that is excited
due the symmetry breaking in the cluster. We study the correlation between the
toroidal response and asymmetry in the metasurface and nanocluster geometries,
which appears from the different diameters of nanodisks or notches introduced
into the nanodisks.Comment: 17 pages, 6 figure
Transmission enhancement in loss-gain multilayers by resonant suppression of reflection
Using the transfer-matrix approach and solving time-domain differential
equations, we analyze the loss compensation mechanism in multilayer systems
composed of an absorbing transparent conductive oxide and dielectric doped with
an active material. We reveal also another regime with the possibility of
enhanced transmission with suppressed reflection originating from the resonant
properties of the multilayers. For obliquely incident and evanescent waves,
such enhanced transmission under suppressed reflection turns into the
reflectionless regime, which is similar to that observed in the PT-symmetric
structures, but does not require PT symmetry. We infer that the reflectionless
transmission is due to the full loss compensation at the resonant wavelengths
of the multilayers.Comment: 12 pages, 10 figure
Electromagnetic wave diffraction by periodic planar metamaterials with nonlinear constituents
We present a theory which explains how to achieve an enhancement of nonlinear
effects in a thin layer of nonlinear medium by involving a planar periodic
structure specially designed to bear a trapped-mode resonant regime. In
particular, the possibility of a nonlinear thin metamaterial to produce the
bistable response at a relatively low input intensity due to a large quality
factor of the trapped-mode resonance is shown. Also a simple design of an
all-dielectric low-loss silicon-based planar metamaterial which can provide an
extremely sharp resonant reflection and transmission is proposed. The designed
metamaterial is envisioned for aggregating with a pumped active medium to
achieve an enhancement of quantum dots luminescence and to produce an
all-dielectric analog of a 'lasing spaser'.Comment: 18 pages, 13 figure
Trapped-mode excitation in all-dielectric metamaterials with loss and gain
Non-Hermitian photonics based on combining loss and gain media within a
single optical system provides a number of approaches to control and generate
the flow of light. In this paper, we show that by introducing non-Hermitian
perturbation into the system with loss and gain constituents, the high-quality
resonances known as trapped modes can be excited without the need to change the
symmetry of the unit cell geometry. To demonstrate this idea, we consider a
widely used all-dielectric planar metamaterial whose unit cell consists of a
pair of rectangular nanoantennas made of ordinal (with loss) and doped (with
gain) silicon. Since the quality factor of the trapped-mode resonance can be
controlled by changing both spatial symmetry and non-Hermiticity, varying loss
and gain allows us to compensate for the influence of asymmetry and restore the
quality factor of the localized mode. The results obtained suggest new ways to
achieve high-quality resonances in non-Hermitian metamaterials promising for
many practical applications in nanophotonics.Comment: 7 pages, 6 figure
Modal Phenomena of Surface and Bulk Polaritons in Magnetic- Semiconductor Superlattices
We discuss peculiarities of bulk and surface polaritons propagating in a composite magnetic-semiconductor superlattice influenced by an external static magnetic field. Three particular configurations of magnetization, namely, the Voigt, polar, and Faraday geometries, are considered. In the long-wavelength limit, involving the effective medium theory, the proposed superlattice is described as an anisotropic uniform medium defined by the tensors of effective permittivity and effective permeability. The study is carried out in the frequency band where the characteristic resonant frequencies of underlying constitutive magnetic and semiconductor materials of the superlattice are different but closely spaced. The effects of mode crossing and anti-crossing in dispersion characteristics of both bulk and surface polaritons are revealed and explained with an assistance of the concept of Morse critical points from the catastrophe theory
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