R. Ghasemi

Metal-dielectric metamaterials for guided wave silicon photonics.

The aim of the present paper is to investigate the potential of metallic metamaterials for building optical functions in guided wave optics at 1.5 µm. A significant part of this work is focused on the optimization of the refractive index variation associated with localized plasmon resonances. The minimization of metal related losses is specifically addressed as well as the engineering of the resonance frequency of the localized plasmons. Our numerical modeling results show that a periodic chain of gold cut wires placed on the top of a 100 nm silicon waveguide makes it possible to achieve a significant index variation in the vicinity of the metamaterial resonance and serve as building blocks for implementing optical functions. The considered solutions are compatible with current nano-fabrication technologies.

Efficient control of a 3D optical mode using a thin sheet of transformation optical medium

We report on a mode adapter that transitions light between two SOI waveguides having different widths. The device has been designed using a two-dimensional embedded coordinate transformation and consists of a thin sheet of a controlled anisotropic material directly placed on top of the Si slab. We demonstrate that this layer effectively controls the flow of energy propagating in the Si slab by performing three-dimensional full-wave simulations. The proposed geometry can be implemented with planar optical metamaterials for various applications in guided optics.

Transformation optics and metamaterials at infrared wavelength: engineering of permittivity and permeability

The transformation optics was introduced by J. Pendry and U. Leonhardt in 2006 [1,2]. In this method an initial space is transformed into a new space and this transformed space can be materialized by a material, which the electromagnetic parameters can be deduced from the metric of the transformed space. In the general case the electromagnetic parameters are anisotropic tensors. At microwave frequencies these materials can be realized using classical metamaterials like SRR form J. Pendry or ELC from D. Smith [3]. At infrared wavelengths this realization is a challenge because the dimensions of the metamaterials are much smaller than the wavelength and become nanometric. Then the design of these metamaterials must be simplified and original methods must be developed to allow the realization of these metamaterials with controlled electromagnetic properties. In this paper we describe the realization of a multilayer metamaterial working at infrared wavelength, which the permittivity and the permeability can be adjusted separately. We give some examples of realized multilayer materials operating around 150THz, with a comparison between the results of full wave simulations of these materials and their characterizations using a Fourier Transform Infrared Spectrometer.

3D opticall metamaterials

This work focuses on the fabrication of 3D infrared metamaterials. We characterize the sample and provide useful guidelines for the design of these structures

Taper of metamaterials designed by optical transformation

In this paper, we present a numerical study of a mode adapter that transitions light from a wide SOI waveguide to a narrower one. The device has been designed using the technique of transformation optics and consists of a thin sheet of anisotropic medium directly placed on top of the Si slab. We demonstrate that this sheet effectively controls the flow of energy propagating in the Si slab and that the structure can be potentially implemented by patterning a single layer of planar optical metamaterial on the SOI waveguide.

Negative refraction in split-ring-resonator stack at normal incidence

Metamaterials building blocks, from microwave to optical range are mainly based on metal-dielectric composite. In almost all structures with true negative index (not coming from losses) two kind of meta-atoms (electric and magnetic) are mixed in order to drive simultaneously the effective permittivity and permeability to negative values and thus to obtain a negative index of refraction. In this paper we show that two coupled structures with localized plasmons modes (e.g. Cut wires or Split-Ring-Resonators) can exhibit negative refractive index by their own, by appropriately controlling the hybridization scheme of the so called plasmons modes. As a result, the metallic filling factor is drastically reduced and low losses especially at optical frequencies may allow realistic applications of metamaterials.