262 research outputs found
A coupling model for quasi-normal modes of photonic resonators
We develop a model for the coupling of quasi-normal modes in open photonic
systems consisting of two resonators. By expressing the modes of the coupled
system as a linear combination of the modes of the individual particles, we
obtain a generalized eigenvalue problem involving small size dense matrices. We
apply this technique to dielectric rod dimmer of rectangular cross section for
Transverse Electric (TE) polarization in a two-dimensional (2D) setup. The
results of our model show excellent agreement with full-wave finite element
simulations. We provide a convergence analysis, and a simplified model with a
few modes to study the influence of the relative position of the two
resonators. This model provides interesting physical insights on the coupling
scheme at stake in such systems and pave the way for systematic and efficient
design and optimization of resonances in more complicated systems, for
applications including sensing, antennae and spectral filtering
Ces jeunes qui ne viennent pas en Mission Locale : du délai de « latence » au phénomène du « non-recours »
Contribution au dossier de la MRI
Finite Element Method
International audienceIn this chapter, we demonstrate a general formulation of the Finite Element Method allowing to calculate the diffraction efficiencies from the electromagnetic field diffracted by arbitrarily shaped gratings embedded in a multilayered stack lightened by a plane wave of arbitrary incidence and polarization angle. It relies on a rigorous treatment of the plane wave sources problem through an equivalent radiation problem with localized sources. Bloch conditions and a new Adaptative Perfectly Matched Layer have been implemented in order to truncate the computational domain. We derive this formulation for both mono-dimensional gratings in TE/TM polarization cases (2D or scalar case) and for the most general bidimensional or crossed gratings (3D or vector case). The main advantage of this formulation is its complete generality with respect to the studied geometries and the material properties. Its principle remains independent of both the number of diffractive elements by period and number of stack layers. The flexibility of our approach makes it a handy and powerful tool for the study of metamaterials, finite size photonic crystals, periodic plasmonic structures..
Quasi-modal analysis of segmented waveguides
International audience—In the present paper, we show that it is possible to use a periodic structure of disconnected elements (e.g. a line of rods) to guide electromagnetic waves, in the direction of the periodicity. To study such segmented waveguides, we use the concept of quasimodes associated to complex frequencies. The numerical determination of quasimodes is based on a finite element formulation completed with Perfectly Matched Layers (PMLs). These PMLs lead to non Hermitian matrices whose complex eigenvalues correspond to quasimode frequencies. Using Floquet-Bloch theory, a numerical model is set up that allows the spectral study of structures that are both open and periodic. With this model, we show that it is possible to guide electromagnetic waves on significant distances with very limited losses
Transmission enhancement through square coaxial apertures arrays in metallic film: when leaky modes filter infrared light
We consider arrays of square coaxial apertures in a gold layer and study
their diffractive behavior in the far infrared region. These structures exhibit
a resonant transmission enhancement that is used to design tunable bandpass
filters. We provide a study of their spectral features and show by a modal
analysis that the resonance peak is due to the excitation of leaky modes of the
open photonic structure. Fourier transform infrared (FTIR) spectrophotometry
transmission measurements of samples deposited on Si substrate show good
agreement with numerical results and demonstrate angular tolerance up to 30
degrees of the fabricated filters.Comment: 4 pages, 3 figure
Resonant metamaterial absorbers for infrared spectral filtering: quasimodal analysis, design, fabrication and characterization
We present a modal analysis of metal-insulator-metal (MIM) based
metamaterials in the far infrared region. These structures can be used as
resonant reflection bandcut spectral filters that are independent of the
polarization and direction of incidence because of the excitation of quasimodes
(modes associated with a complex frequency) leading to quasi-total absorption.
We fabricated large area samples made of chromium nanorod gratings on top of
Si/Cr layers deposited on silicon substrate and measurements by Fourier
Transform spectrophotometry show good agreement with finite element
simulations. A quasimodal expansion method is developed to obtain a reduced
order model that fits very well full wave simulations and that highlights
excitation conditions of the modes.Comment: 8 pages, 7 figure
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