2,495 research outputs found
Nonlinear directional coupler for polychromatic light
We demonstrate that nonlinear directional coupler with special bending of
waveguide axes can be used for all-optical switching of polychromatic light
with very broad spectrum covering all visible region. The bandwidth of
suggested device is enhanced five times compared to conventional couplers. Our
results suggest novel opportunities for creation of all-optical logical gates
and switches for polychromatic light with white-light and super-continuum
spectrum.Comment: 3 pages, 3 figure
Shaping and control of polychromatic light in nonlinear photonic lattices
We overview our recent results on spatio-spectral control,
diffraction management, broadband switching, and self-trapping of polychromatic
light in periodic photonic lattices in the form of rainbow gap
solitons, polychromatic surface waves, and multigap color breathers. We
show that an interplay of wave scattering from a periodic structure and
interaction of multiple colors in media with slow nonlinear response can
be used to selectively separate or combine different spectral components.
We use an array of optical waveguides fabricated in a LiNbO3 crystal to
actively control the output spectrum of the supercontinuum radiation and
generate polychromatic gap solitons through a sharp transition from spatial
separation of spectral components to the simultaneous spatio-spectral localization
of supercontinuum light. We also show that by introducing specially
optimized periodic bending of waveguides in the longitudinal direction, one
can manage the strength and type of diffraction in an ultra-broad spectral
region and, in particular, realize the multicolor Talbot effect
Polychromatic gap solitons and breathers in nonlinear waveguide arrays
We predict the spatial localization of multiple wavelength components in the form of stationary polychromatic gap solitons and dynamic multi-gap breathers, and observe experimentally tunable spatio-spectral trapping of supercontinuum radiation in nonlinear periodic photonic structures
Shaping and switching of polychromatic light in arrays of periodically curved nonlinear waveguides
We overview our recent theoretical results on spatio-spectral control, diffraction management, and broadband all-optical switching of polychromatic light in periodically curved one and two dimensional arrays of coupled optical waveguides. In particular, we show that polychromatic light beams and patterns produced by white-light and supercontinuum sources can experience wavelength-independent normal, anomalous, or zero diffraction in specially designed structures. We also demonstrate that in the nonlinear regime, it is possible to achieve broadband all-optical switching of polychromatic light in a directional waveguide coupler with special bending of the waveguide axes. Our results suggest novel opportunities for creation of all-optical logical gates and switches which can operate in a very broad frequency region, e.g., covering the entire visible spectrum
Temporal Rainbow Scattering at Boundary-Induced Time Interfaces
Since the dawn of modern optics and electromagnetics, optical prism is one of
the most fascinating optical elements for refracting light. Exploiting its
frequency dispersive behaviour, a prism is able to refract different
frequencies in different directions, realizing polychromatic light rainbows.
Recently, thanks to their engineerable electromagnetic response, metamaterials
have been exploited for achieving novel refractive scattering processes, going
beyond the classical prism effects. In this Manuscript, we report on a novel
rainbow-like scattering process taking place at the interface of a
boundary-induced temporal metamaterial realized by instantaneously opening the
boundary conditions of a parallel plate waveguide. Changing abruptly the
conductivity of one of the two metallic plates, we demonstrate that an
equivalent temporal interface between two different media is realized, and the
monochromatic wave propagating into the waveguide gets scattered into a
polychromatic rainbow in free-space. We derive the relationships between the
waveguide mode and the raising rainbow in terms of scattered amplitude and
frequencies as a function of the elevation angle with respect to the waveguide
axis. We apply the underlying physics to control the temporal rainbow by
imposing a principal direction of scattering by design. Full-wave numerical
simulations are performed for computing the rainbow temporal scattering and
verifying the design guidelines for achieving controlled temporal rainbow
scattering.Comment: 14 pages, 3 figures, Appendi
Efficient radiative transfer modelling with SKIRT
We present SKIRT, a three-dimensional Monte Carlo radiative transfer code
developed to study dusty galaxies. We discuss SKIRT's most important
characteristics and present a number of applications. In particular, we focus
on the kinematical aspect of SKIRT. We demonstrate that dust attenuation mimics
the presence of dark matter around elliptical galaxies and that it severely
affects the rotation curves of edge-on galaxies.Comment: 12 pages, 5 figures. To appear in "The Spectral Energy Distribution
of Gas-Rich Galaxies: Confronting Models with Data", eds. C.C. Popescu and
R.J. Tuffs, AIP Conference Series. A version with high resolution figures can
be found at http://allserv.ugent.be/~mbaes/AIP.ps.g
Feasibility of thickness mapping using ultrasonic guided waves
Detection and sizing of corrosion in pipelines and pressure vessels over large, partially
accessible areas is of growing interest in the petrochemical and nuclear industries.
Traditionally, conventional ultrasonic thickness gauging and eddy current techniques
have been used to precisely measure the thickness in structures. These techniques
only allow the measurement of the local thickness under the probe. Consequently
obtaining the remnant thickness of a specimen over a large area requires the probe to
be scanned, which is a long and tedious process. Moreover, with these techniques,
the scanning may become impossible when the area of inspection is inaccessible.
There is therefore a need for a rapid, accurate, long range inspection technique to
measure the remaining thickness in corrosion patches.
Low frequency guided waves are now routinely used to screen large area of pipes and
other structures for cracks and corrosion. Their detection and location capability is
very good, but the standard screening technique only gives a rough estimate of the
remaining wall thickness. Guided waves have multiple properties which can be used
for thickness mapping over large partially accessible areas e.g. dispersion and cutoff
frequency thickness product of the high order modes.
The present work aims to demonstrate the potential of guided waves for thickness
mapping over large partially accessible areas. It starts with a general introduction
on ultrasonic guided waves and a literature review of the different techniques for the
evaluation of thickness with guided waves. The severity of the errors introduced in
time-of-flight tomography for thickness reconstruction by breaking the assumption
of the ray theory are investigated. As these errors are significant, the possibility of
using the cutoff property of the high order modes is investigated in a frequency range
where the ray theory is valid. It is found that the attenuation due to the scattering
of the waves in corrosion is too large for this technique to work. Finally the use of
low frequency guided wave for diffraction tomography is examined. Finite element
simulations of a 64 element circular array on a plate show that when the scattering
mechanism of the object to be reconstructed satisfies the Born approximation the reconstruction of the thickness is accurate. However the practical implementation is
more challenging when the incident field is not known. Experimental results demonstrate
that ultimately the scattering from the array of transducer is a major source
of error in the tomographic reconstruction, but when there is no scattering from
the array of transducers the reconstructions are very similar to the finite element
simulations
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