Optical meta-materials

The term metamaterial was introduced by J. B. Pendry in 1999. It designates an artificial material structured on a scale smaller than the working wavelength, in order to obtain singular properties, i.e. properties that are not accessible from homogeneous materials. This general concept can be applied to all fields of physics involving wave propagation. In particular, the field of acoustic metamaterials has seen significant development in recent years. However, most of the work published to date concerns the field of electromagnetic waves.

In the case of sub-wavelength structuring, the artificial material can be considered as a medium described by effective permittivity and permeability. Although homogenization processes continue to give rise to debate, particularly as regards their conditions of application, there is a consensus on the notion of openness of parameter space, which makes it possible to envisage metamaterials with positive, zero or negative effective permittivity and permeability. The first experimental demonstrations consisted in demonstrating a negative refractive index obtained by overlapping zones of negative permittivity and permeability. This possibility, imagined as early as 1962 by V. Veselago, opened the door to new applications. The idea of the superlens, introduced by J. B. Pendry in 2000, is part of this context. Although the prospects in the field of optics appeared very promising, the majority of the first experiments were carried out on devices operating in microwaves. Quite apart from the problem of metal losses, the transfer of metamaterial technologies used in microwaves to optical wavelengths has come up against a number of obstacles, notably in the design and manufacture of structures with a negative refractive index. However, the infrared and visible wavelengths are increasingly being studied. While this development reflects undeniable technological progress, its main driving force lies in the diversity of applications envisaged, most of which do not require the synthesis of a negative-index medium. This is notably the case for the invisibility cloak application, which in its most simplified conception can be based on a single parameter gradient (permittivity, permeability or refractive index) with positive values.

In this article, we begin by describing the particularities of the optical spectrum and their consequences for the various stages in the development of metamaterials, from the modeling of physical phenomena to the analysis of the dispersion properties of structures. The second part will focus on the various fields of application. In view of the importance of non-linear phenomena in optical technologies, this topic will be addressed in the third part, before opening the analysis to the various prospects for development....