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Antoine Moreau

Publications and source records attributed to Antoine Moreau.

30 records · Page 2Linked to original sources
arXiv2014

Nonlocality in metallo-dielectric multilayers: numerical tools and physical analysis

We provide theoretical and numerical tools to quantitatively study the impact of nonlocality arising from free electrons in metals on the optical properties of metallo-dielectric multilayers. Though effects due to nonlocality are in general quite small, they nevertheless can be important for very thin (typically below 10 nm) metallic layers - as are used in structures characterized by relatively flat dispersion curves. Such structures include those with negative refractive index; hyperbolic metamaterials; and materials with index near zero. We find in all cases that the inclusion of nonlocal effects through application of the hydrodynamic model to the electron response leads to a higher transmission through the considered medium. Finally, we examine the excitation of gap-plasmon resonances, where nonlocality plays a much greater role, and suggest possible routes for experimental investigation.

physics.optics↗
arXiv2013

Ultimate resolution of indefinite metamaterial flat lenses

We show that any metallo-dielectric multilayer with a hyperbolic dispersion relation can actually be characterized by a complex effective index. This refractive index, extracted from the complex Bloch band diagram, can be directly linked to the super-resolution of a flat lens made of this so- called indefinite metamaterials. This allows for a systematic optimization of the lens design, leading to structures that are outperforming state-of-art flat lenses. We show that, even when fully taking absorption into account, our design provides super-resolved images for visible light up to a distance of one wavelength from the lens edge.

physics.optics↗
arXiv2012

The impact of nonlocal response on metallo-dielectric multilayers and optical patch antennas

We analyze the impact of nonlocality on the waveguide modes of metallo-dielectric multilayers and optical patch antennas, the latter formed from metal strips closely spaced above a metallic plane. We model both the nonlocal effects associated with the conduction electrons of the metal, as well as the previously overlooked response of bound electrons. We show that the fundamental mode of a metal-dielectric-metal waveguide, sometimes called the gap-plasmon, is very sensitive to nonlocality when the insulating, dielectric layers are thinner than 5 nm. We suggest that optical patch antennas, which can easily be fabricated with controlled dielectric spacer layers and can be interrogated using far-field scattering, can enable the measurement of nonlocality in metals with good accuracy.

physics.optics↗
arXiv2012

Optically optimal wavelength-scale patterned ITO/ZnO composite coatings for thin film solar cells

A methodology is proposed for finding structures that are, optically speaking, locally optimal : a physical analysis of much simpler structures is used to constrain the optimization process. The obtained designs are based on a flat amorphous silicon layer (to minimize recombination) with a patterned anti-reflective coating made of ITO or ZnO, or a composite ITO/ZnO coating. These latter structures are realistic and present good performances despite very thin active layers.

physics.optics↗
arXiv2011

Mesoscopic self-collimation and slow light in all-positive index layered photonic crystals

We demonstrate a mesoscopic self-collimation effect in photonic crystal superlattices consisting of a periodic set of all-positive index 2D photonic crystal and homogeneous layers. We develop an electromagnetic theory showing that diffraction-free beams are observed when the curvature of the optical dispersion relation is properly compensated for. This approach allows to combine slow light regime together with self-collimation in photonic crystal superlattices presenting an extremely low filling ratio in air.

physics.optics↗
arXiv2011

Large negative lateral shifts due to negative refraction

When a thin structure in which negative refraction occurs (a metallo-dielectric or a photonic crystal) is illuminated by a beam, the reflected and transmitted beam can undergo a large negative lateral shift. This phenomenon can be seen as an interferential enhancement of the geometrical shift and can be considered as a signature of negative refraction.

physics.optics↗
arXiv2010

Light wheel buildup using a backward surface mode

When a guided mode is excited in a dielectric slab coupled to a backward surface wave at the interface between a dielectric and a left-handed medium, light is confined in the structure : this is a light wheel. Complex plane analysis of the dispersion relation and coupled-mode formalism give a deep insight into the physics of this phenomenon (lateral confinement and the presence of a dark zone).

physics.optics↗
arXiv2008

Leaky modes of a left-handed slab

Using complex plane analysis we show that left-handed slab may support either leaky slab waves, which are backward because of negative refraction, or leaky surface waves, which are backward or forward depending on the propagation direction of the surface wave itself. Moreover, there is a general connection between the reflection coefficient of the left-handed slab and the one of the corresponding right-handed slab (with opposite permittivity and permeability) so that leaky slab modes are excited for the same angle of incidence of the impinging beam for both structures. Many negative giant lateral shifts can be explained by the excitation of these leaky modes.

physics.optics↗
arXiv2007

Localization of light in a lamellar structure with left-handed medium : the light wheel

The contra-directional coupling between a left-handed monomode waveguide and a right-handed monomode waveguide is rigorously studied using a complex plane analysis. Light is shown to rotate in this lamellar structure forming a very exotic mode which we have called a light wheel. The light wheel can be excited using evanescent coupling or by placing sources in one of the waveguides. This structure can thus be seen as a new type of cavity. It is a way to suppress the guided mode of a dielectric slab.

physics.optics↗
arXiv2006

Enhanced transmission of slit arrays in an extremely thin metallic film

Horizontal resonances of slit arrays are studied. They can lead to an enhanced transmission that cannot be explained using the single-mode approximation. A new type of cavity resonance is found when the slits are narrow for a wavelength very close to the period. It can be excited for very low thicknesses. Optimization shows these structures could constitute interesting monochromatic filters.

physics.optics↗
arXiv2006

Optimal estimation for Large-Eddy Simulation of turbulence and application to the analysis of subgrid models

The tools of optimal estimation are applied to the study of subgrid models for Large-Eddy Simulation of turbulence. The concept of optimal estimator is introduced and its properties are analyzed in the context of applications to a priori tests of subgrid models. Attention is focused on the Cook and Riley model in the case of a scalar field in isotropic turbulence. Using DNS data, the relevance of the beta assumption is estimated by computing (i) generalized optimal estimators and (ii) the error brought by this assumption alone. Optimal estimators are computed for the subgrid variance using various sets of variables and various techniques (histograms and neural networks). It is shown that optimal estimators allow a thorough exploration of models. Neural networks are proved to be relevant and very efficient in this framework, and further usages are suggested.

physics.class-ph↗