55 research outputs found
Dark-field hyperlens: Super-resolution imaging of weakly scattering objects
We propose and numerically demonstrate a technique for subwavelength imaging
based on a metal-dielectric multilayer hyperlens designed in such a way that
only the large-wavevector waves are transmitted while all propagating waves
from the image area are blocked by the hyperlens. As a result, the image plane
only contains scattered light from subwavelength features of the objects and is
free from background illumination. Similar in spirit to conventional dark-field
microscopy, the proposed dark-field hyperlens is promising for optical imaging
of weakly scattering subwavelength objects, such as optical nanoscopy of
label-free biological objects.Comment: 6 figure
Optical memory based on ultrafast wavelength switching in a bistable microlaser
We propose an optical memory cell based on ultrafast wavelength switching in
coupled-cavity microlasers, featuring bistability between modes separated by
several nanometers. A numerical implementation is demonstrated by simulating a
two-dimensional photonic crystal microlaser. Switching times of less than 10
ps, switching energy around 15--30 fJ and on-off contrast of more than 40 dB
are achieved. Theoretical guidelines for optimizing the performance of the
memory cell in terms of switching time and energy are drawn.Comment: to appear in Optics Letter
Bismuth ferrite as low-loss switchable material for plasmonic waveguide modulator
We propose new designs of plasmonic modulators, which can be utilized for
dynamic signal switching in photonic integrated circuits. We study performance
of plasmonic waveguide modulator with bismuth ferrite as an active material.
The bismuth ferrite core is sandwiched between metal plates
(metal-insulator-metal configuration), which also serve as electrodes so that
the core changes its refractive index under applied voltage by means of partial
in-plane to out-of-plane reorientation of ferroelectric domains in bismuth
ferrite. This domain switch results in changing of propagation constant and
absorption coefficient, and thus either phase or amplitude control can be
implemented. Efficient modulation performance is achieved because of high field
confinement between the metal layers, as well as the existence of mode cut-offs
for particular values of the core thickness, making it possible to control the
signal with superior modulation depth. For the phase control scheme, {\pi}
phase shift is provided by 0.8-{\mu}m length device having propagation losses
0.29 dB/{\mu}m. For the amplitude control, we predict up to 38 dB/{\mu}m
extinction ratio with 1.2 dB/{\mu}m propagation loss. In contrast to previously
proposed active materials, bismuth ferrite has nearly zero material losses, so
bismuth ferrite based modulators do not bring about additional decay of the
propagating signal
From surface to volume plasmons in hyperbolic metamaterials: General existence conditions for bulk high-k waves in metal-dielectric and graphene-dielectric multilayers
We theoretically investigate general existence conditions for broadband bulk
large-wavevector (high-k) propagating waves (such as volume plasmon polaritons
in hyperbolic metamaterials) in subwavelength periodic multilayer structures.
Describing the elementary excitation in the unit cell of the structure by a
generalized resonance pole of a reflection coefficient, and using Bloch's
theorem, we derive analytical expressions for the band of large-wavevector
propagating solutions. We apply our formalism to determine the high-k band
existence in two important cases: the well-known metal-dielectric, and recently
introduced graphene-dielectric stacks. We confirm that short-range surface
plasmons in thin metal layers can give rise to hyperbolic metamaterial
properties, and demonstrate that long-range surface plasmons cannot. We also
show that graphene-dielectric multilayers tend to support high-k waves and
explore the range of parameters for which this is possible, confirming the
prospects of using graphene for materials with hyperbolic dispersion. The
approach is applicable to a large variety of structures, such as continuous or
structured microwave, terahertz (THz) and optical metamaterials.Comment: 9 pages, 5 figure
Photonic band-gap engineering for volume plasmon polaritons in multiscale multilayer hyperbolic metamaterials
We theoretically study the propagation of large-wavevector waves (volume
plasmon polaritons) in multilayer hyperbolic metamaterials with two levels of
structuring. We show that when the parameters of a subwavelength
metal-dielectric multilayer ("substructure") are modulated ("superstructured")
on a larger, wavelength scale, the propagation of volume plasmon polaritons in
the resulting multiscale hyperbolic metamaterials is subject to photonic band
gap phenomena. A great degree of control over such plasmons can be exerted by
varying the superstructure geometry. When this geometry is periodic, stop bands
due to Bragg reflection form within the volume plasmonic band. When a cavity
layer is introduced in an otherwise periodic superstructure, resonance peaks of
the Fabry-Perot nature are present within the stop bands. More complicated
superstructure geometries are also considered. For example, fractal Cantor-like
multiscale metamaterials are found to exhibit characteristic self-similar
spectral signatures in the volume plasmonic band. Multiscale hyperbolic
metamaterials are shown to be a promising platform for large-wavevector bulk
plasmonic waves, whether they are considered for use as a new kind of
information carrier or for far-field subwavelength imaging.Comment: 12 pages, 10 figures, now includes Appendix
Asymmetric transmission in planar chiral split-ring metamaterials: Microscopic Lorentz-theory approach
The electronic Lorentz theory is employed to explain the optical properties of planar split-ring metamaterials.
Starting from the dynamics of individual free carriers, the electromagnetic response of an individual split-ring
meta-atom is determined, and the effective permittivity tensor of the metamaterial is calculated for normal
incidence of light. Whenever the split ring lacks in-plane mirror symmetry, the corresponding permittivity
tensor has a crystallographic structure of an elliptically dichroic medium, and the metamaterial exhibits optical
properties of planar chiral structures. Its transmission spectra are different for right-handed versus left-handed
circular polarization of the incident wave, so the structure changes its transmittance when the direction of
incidence is reversed. The magnitude of this change is shown to be related to the geometric parameters of the split
ring. The proposed approach can be generalized to a wide variety of metal-dielectric metamaterial geometries
Plasmonic rod dimers as elementary planar chiral meta-atoms
Electromagnetic response of metallic rod dimers is theoretically calculated
for arbitrary planar arrangement of rods in the dimer. It is shown that dimers
without an in-plane symmetry axis exhibit elliptical dichroism and act as
"atoms" in planar chiral metamaterials. Due to a very simple geometry of the
rod dimer, such planar metamaterials are much easier in fabrication than
conventional split-ring or gammadion-type structures, and lend themselves to a
simple analytical treatment based on coupled dipole model. Dependencies of
metamaterial's directional asymmetry on the dimer's geometry are established
analytically and confirmed in numerical simulations.Comment: 3 page
Transition absorption as a mechanism of surface photoelectron emission from metals
Transition absorption of electromagnetic field energy by an electron passing
through a boundary between two media with different dielectric permittivities
is considered both classically and quantum mechanically. It is shown that
transition absorption can make a substantial contribution to the process of
electron photoemission from metals due to the surface photoelectric effect.Comment: 4 pages, 3 figure
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