Near-field properties of plasmonic nanostructures with high aspect ratio

Using the Green's dyad technique based on cuboidal meshing, we compute the electromagnetic field scattered by metal nanorods with high aspect ratio. We investigate the effect of the meshing shape on the numerical simulations. We observe that discretizing the object with cells with aspect ratios similar to the object's aspect ratio improves the computations, without degrading the convergency. We also compare our numerical simulations to finite element method and discuss further possible improvements

Homogenization of nonlocal wire metamaterial via a renormalization approach

It is well known that defining a local refractive index for a metamaterial requires that the wavelength be large with respect to the scale of its microscopic structure (generally the period). However, the converse does not hold. There are simple structures, such as the infinite, perfectly conducting wire medium, which remain non-local for arbitrarily large wavelength-to-period ratios. In this work we extend these results to the more realistic and relevant case of finite wire media with finite conductivity. In the quasi-static regime the metamaterial is described by a non-local permittivity which is obtained analytically using a two-scale renormalization approach. Its accuracy is tested and confirmed numerically via full vector 3D finite element calculations. Moreover, finite wire media exhibit large absorption with small reflection, while their low fill factor allows considerable freedom to control other characteristics of the metamaterial such as its mechanical, thermal or chemical robustness.Comment: 8 pages on two columns, 7 figures, submitted to Phys. Rev.

Transformations géométriques réelles et complexes (application à la recherche de modes à pertes dans des fibres optiques microstructurées)

Le travail présenté dans ce manuscrit est centré sur l'utilisation des transformations géométriques réelles et complexes combinées avec la méthode des éléments finis, pour le calcul des modes à pertes dans les fibres optiques microstructurées. En premier lieu nous nous sommes intéressés au cas monodimensionnel (structure de type Pérot-Fabry) ; nous avons alors testé deux méthodes numériques différentes. La première que nous avons appelée tétrachotomie où la recherche de modes à pertes se réduit à la recherche de pôles dans le plan complexe du coefficient de réflexion. La seconde est une méthode de type éléments finis combinée avec les PMLs (Perfectly Matched Layer). La deuxième partie de la thèse est consacrée à l'étude des fibres optiques microstructurées. Dans une premier temps, nous avons comparé notre méthode avec la méthode multipolaire dans le cas d'inclusions simples (trous circulaires) et nous avons constaté un excellent accord. Dans un deuxième temps, on a étudié des fibres plus exotiques comme les fibres anisotropes, les fibres dont les inclusions ont de forme arbitraire et les fibres à gradient d'indice. Enfin, la combinaison de deux transformations géométriques, l'une réelle associée à un changement de coordonnées hélicoïdales, l'autre complexe associée aux PMLs adaptées à notre problème, nous a permis de se ramener à l'étude d'une fibre anisotrope électriquement et magnétiquement, mais invariante par translation. On a alors étudié, pour la première fois, l'impact de la torsion sur les modes à pertes dans les FOMsAIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Leaky modes in twisted microstructured fibres

International audienc

Geometrical transformations and equivalent materials in computational electromagnetism

Purpose – This paper aims to review various techniques used in computational electromagnetism such as the treatment of open problems, helicoidal geometries and the design of arbitrarily shaped invisibility cloaks. This seemingly heterogeneous list is unified by the concept of geometrical transformation that leads to equivalent materials. The practical set-up is conveniently effected via the finite element method. Design/methodology/approach – The change of coordinates is completely encapsulated in the material properties. Findings – The most significant examples are the simple 2D treatment of helicoidal geometries and the design of arbitrarily shaped invisibility cloaks. Originality/value – The paper provides a unifying point of view, bridging several techniques in electromagnetism

On the use of PML for the computation of leaky modes An application to microstructured optical fibres

International audienceThe purpose of this paper is to present a complete analysis of leaky modes within a microstructured optical fibre (MOF). Some new numerical results illustrating the versatility and accuracy of our approach are to be given

Near-Field Properties of Plasmonic Nanostructures with High Aspect Ratio

International audienceUsing the Green's dyad technique based on cuboidal meshing, we compute the electromagnetic field scattered by metal nanorods with high aspect ratio. We investigate the effect of the meshing shape on the numerical simulations. We observe that discretizing the object with cells with aspect ratios similar to the object's aspect ratio improves the computations, without degrading the convergency. We also compare our numerical simulations to finite element method and discuss further possible improvements