Gérard Tayeb

Aix-Marseille University | AMU · Institut Fresnel (UMR 7249 FRESNEL)

Ultrahigh-field (UHF) magnetic resonance imaging (MRI) systems are getting a lot of attention as they ensure high intrinsic signal-to-noise ratio resulting in higher spatial and temporal resolutions as well as better contrast. This promises improved clinical results with regard to morphological as well as functional and metabolic capabilities. Trad...

This paper reports a fishnet hyperbolic metamaterial that mimics the electromagnetic properties of magnetically confined plasma. These electromagnetic properties are strongly anisotropic and different from any conventional material, therefore cannot be mimicked by bulk materials. The structure is made of a stack of thin copper grids spaced by Rohac...

Parallel transmission is a very promising method to tackle B1⁺ field inhomogeneities at ultrahigh field in magnetic resonant imaging (MRI). This technique is however limited by the mutual coupling between the radiating elements. Here we propose to solve this problem by designing a passive magneto-electric resonator that we here refer to as stacked...

We first review basic equations of plasmonics in anisotropic media. We recall the origin of Maxwell's gradient index fisheye lens. We then apply tools of transformation optics to the design of a cyclic concentrator and a variety of plasmonic carpet-cloaks. We further give a brief account of the discovery of spoof plasmon polaritons (SfPPs) by Pendr...

We investigate dynamic effective anisotropy in photonic crystals (PCs) through a combination of an effective medium theory, which is a high-frequency homogenization (HFH) method explicitly developed to operate for short waves, as well as through numerical simulations and microwave experiments. The HFH yields accurate predictions of the effective an...

Plasmonic resonances in metallic nanoparticles are exploited to create efficient optical filtering functions. A finite element method is used to model metallic nanoparticle gratings. The accuracy of this method is shown by comparing numerical results with measurements on a two-dimensional grating of gold nanocylinders with an elliptic cross section...

L'invention porte sur un dispositif de vision tête haute pour un conducteur de véhicule, comprenant un dispositif de projection d'image (20) et un système optique (40) comprenant une lame (30) réfléchissante, le système optique (40) étant configuré de telle sorte qu'une image nette se forme à une distance prédéterminée du conducteur, ladite image c...

Sunscreens protect from UV radiation, a carcinogen also responsible for sunburns and age-associated dryness. In order to anticipate the transmission of light through UV protection containing scattering particles, we implement electromagnetic models, using numerical methods for solving Maxwell’s equations. After having our models validated, we compa...

Filtering properties of periodic arrays of metallic nanoparticles are investigated. Effect of the width, height and spacing of the particles are theoretically shown. Comparisons of numerical simulations with measurements are provided.

We demonstrate the possibility to obtain perfect blazing both in Littrow and off-Littrow mountings using diffractive systems consisting of a plane metallic substrate and dielectric structures that can support cavity modes. The resonances are located at a relatively large distance between the metal and the dielectric structure, a condition that prev...

A dielectric structure with effective permittivity and permeability close to − 1 operating for propagative waves at optical wavelengths is proposed. This structure is a two-dimensional photonic crystal with refractive index − 1 , coated by appropriate antireflection gratings. Numerical simulations involving a flat lens made of this optimized crysta...

We propose a theoretical study of optimization of metal-dielectric multilayer in order to approach $-1$ effective refractive index for transverse magnetic waves and a wavelength in the visible. The absorption losses of metal appear to be a crucial factor that affects the effective properties of the multilayer. Taking advantage of the dispersion rel...

In this paper, we study the radiation from embedded sources in two-dimensional finite-size "photonic-quasicrystal" (PQC) slabs made of dielectric rods arranged according to a 12-fold sym-metric aperiodic tiling. The results from our investigation, based on rigorous full-wave simulations, show the possibility of achieving broadside radiation at mult...

Modal methods often used to model lamellar gratings that include infinitely or highly conducting metallic parts encounter numerical instabilities in some situations. In this paper, the origin of these numerical instabilities is determined, and then a stable algorithm solving this problem is proposed. In order to complete this analysis, the differen...

We consider cloaking by a coated cylindrical system using plasmonic resonance, and extend previous quasistatic treatments to include the effect of finite wavelength. We show that a probe cylinder can still be cloaked at finite wavelengths, but the cloaking cylinder develops a non-zero scattering cross-section. We show that this latter effect is dom...

We show that the LDOS of a Penrose-type quasicrystal exhibits small additional band gaps. We also investigate the properties of the resonant modes that occur in the transparency bands of photonic quasicrystals.

Hard surfaces or magnetic surfaces can be used to propagate quasi-TEM modes inside closed waveguides. The interesting feature of these modes is an almost uniform field distribution inside the waveguide. But the mechanisms governing how these surfaces act, how they can be characterized, and further how the modes propagate are not detailed in the lit...

Lamellar gratings illuminated in conical (off-plane) mounting can achieve with suitable optogeometrical parameters (grating profile, angle of incidence and wavelength) a total absorption of light for any polarization provided there is only the zeroth propagating order. A detailed analysis shows that electromagnetic resonances are involved and their...

In this paper, we present a comparative study of the emission properties of line sources embedded in two-dimensional finite-size aperiodically-ordered "photonic-quasicrystal" slabs made of dielectric cylinders arranged according to representative categories of aperiodic tilings. Our study, based on a rigorous full-wave numerical method, indicates t...

This paper describes transport properties of linear water waves propagating within a square array of fixed square cylinders. The main focus is on achieving the conditions for all-angle-negative-refraction (AANR) thanks to anomalous dispersion in fluid-filled periodic structures. Of particular interest are two limit cases when either the edges or th...

It is widely believed that a one-dimensional (1D) periodic layered structure with ordinary materials can only have a band gap for certain propagation directions. However, we reveal that a 1D metal-dielectric periodic structure can trap transverse magnetic waves for any angle of propagation in a plane, owing to the existence of a two-dimensional (2D...

This letter deals with a study of aperiodically ordered textured (mushroom-type) high-impedance surfaces (HISs), and their possible application as artificial-magnetic-conductor ground-planes for low-profile directive antennas. In this framework, results from full-wave simulations are presented in order to characterize the electromagnetic response (...

We report on directive, low-sidelobe emission from embedded sources in finite-size aperiodically-ordered "photonic-quasicrystal'' slabs. Our investigation deals with a two-dimensional structure made of dielectric rods arranged according to a 12-fold symmetric aperiodic tiling, and involves a body of parametric studies based on rigorous full-wave si...

We present a numerical study of whispering modes in gratings made of fibers. Due to the strong localization of the modes inside each fiber, it is possible to obtain narrow-band filters with very broad angular tolerance.

This paper deals with a study of textured (mushroom-type) high-impedance substrates based on aperiodic-tiling geometries. In this connection, preliminary results from full-wave simulations are presented in order to explore possible applications as artificial-magnetic-conductor ground-planes for low-profile directive antennas.

Negative refractive index materials are known to be able to support a host of surface plasmon states for both polarizations of light. This makes possible unique effects such as a perfect lens. Checkerboards consisting of alternating cells of positive and negative refractive index represent a very singular situation in which the density of modes div...

We propose a theoretical study of the optimization of one dimensional metal-dielectric metamaterials in order to approach -1 effective optical index. Taking into account actual values of dielectric constants of metal (silver) and dielectrics (HfO2, GaP), and taking advantage of the dispersion relation of Bloch modes, we get a silver/HfO2 metamateri...

We present here a finite slab of triangular checkerboard of negative refractive index material that exhibits a form of extraordinary transmission. We show that such a checkerboard can be used to confine light and can act as an open resonator. Effectively even a single point of intersection between three triangular wedges of negative refractive inde...

We present a numerical method based on the method of the fictitious sources to model one or several inclusions of arbitrary shape in stratified media. Our aim is to propose an efficient numerical method for the modelling of plasmonic devices. Indeed, metals impose rapid decays of the electromagnetic fields that are often a problem for methods based...

The concept of negative index materials has been introduced by V. G. Veselago [1]. J. B. Pendry remarked that such materials should permit to realize a new flat lens with, a priori, unlimited resolution [2]. Although there is some controversial discussion about the negative index materials, it is clear that the amplification of the evanescent waves...

This letter is concerned with a comparative study of the electromagnetic properties of two-dimensional, finite-size, aperiodically ordered "quasi-crystal" dielectric structures based on representative categories of "aperiodic-tiling" geometries. In this framework, a rigorous full-wave solver is used to explore the electromagnetic bandgap and direct...

We investigate the properties of the resonant modes that occur in the transparency bands of two-dimensional finite-size Penrose-type photonic quasicrystals made of dielectric cylindrical rods. These modes stem from the natural local arrangements of the quasicrystal structure rather than, as originally thought, from fabrication-related imperfections...

We consider a dielectric photonic crystal made of cylindrical holes in a high index matrix. We show that a given finite size photonic crystal can mimic a homogeneous material whose permittivity and permeability are negative. We pay attention to the limitation of the homogeneous medium model and the vital role of the truncation of the crystal.

We report the design of a directive antenna using the electromagnetic resonances of a Fabry-Perot cavity. The Fabry-Perot cavity is made of a ground plane and a single metallic grid. The resonance is excited by a patch antenna placed in the cavity at the vicinity of the ground plane. The two remarkable features of Fabry-Perot cavity antennas are, f...

Effective properties of photonic crystals are investigated using a new theoretical method. In the one-dimensional case, analytic expressions of permittivity and permeability of an anisotropic and homogeneous equivalent are obtained. From this analysis, we show that the effective permittivity and permeability can have very small variations in a wide...

In a recent paper, J.B. Pendry [J.B. Pendry, Negative refraction makes a perfect lens, Phys. Rev. Lett. 86 (2000) 3966-3969] has mentioned the possibility of making perfect lenses using a slab of left-handed material with relative permeability and permittivity equal to -1. He gave a demonstration of the vital influence of the evanescent waves in th...

This Letter presents a study of the local density of states (LDOS) in photonic quasicrystals. We show that the LDOS of a Penrose-type quasicrystal exhibits small additional band gaps. Among the band gaps, some exhibit a behavior similar to that typical of photonic crystals, while others do not. The development of certain band gaps requires large-si...

This paper presents a study of the band-gap properties of aperiodically-ordered "quasicrystal" structures. Our long-range plans are aimed at exploring the role of weak forms of "order" and "symmetry" in the band-gap formation, and their possible exploitation for response control and/or optimization. The present preliminary study is concerned with c...

The diffraction of an electromagnetic wave by a cylindrical object with arbitrary cross section is studied by taking advantage of recent progress in grating theories. The fast Fourier factorization method previously developed in Cartesian coordinates is extended to cylindrical coordinates thanks to the periodicity of both the diffracting object and...

We describe a way to combine the method of fictitious sources and the scattering-matrix method. The resulting method presents concurrently the advantages of these two rigorous methods. It is able to solve efficiently electromagnetic problems in which the structure is made up of a jacket containing an arbitrary set of scatterers. The method is descr...

In the recent years, many experimental and theoretical achievements have shown that meta-materials can simulate homogeneous materials with optical index less than unity or even negative. For example, a dielectric photonic crystal, used at the edge of a band gap, can generate phenomena of ultra-refraction (positive index less than unity) or negative...

Enhanced transmission through subwavelength slit gratings and hole arrays is studied in view of its application in the far-infrared and microwave domains. Because for perfectly conducting gratings, plasmon resonances are not expected to produce an enhanced transmission, other kinds of resonance, such as Fabry-Perot, waveguide-mode, and cavity-mode...

Proceedings on CD-ROM (4 pages)

We review several effects that arise from the richness of the dispersion relation of the electromagnetic bandgap materials (EBGMs). Indeed, EBGMs could simulate homogenous material whose optical index is lower than one or even negative (at least for the refraction). We take advantage of this property to design a lens with very short focal length or...