Exploring metamaterial horizons: New concepts and geometrical tools for the description of advanced electromagnetic phenomena

Einstein’s theory of general relativity has dramatically changed our world view, by describing gravity as an intrinsic deformation of space and time. About fifteen years ago, John Pendry and Ulf Leonhardt had the intriguing idea to emulate the behaviour of light in a deformed space by making use of carefully designed artificial metamaterials. Metamaterials consist of elements that are very small with respect to the characteristic length of light waves. By optimizing the shape, the density, and the size of these elements, metamaterials can control light rays in a very precise way. A priori, it is very difficult, if not impossible, to determine what metamaterial propertiesimpose a desired bend, split, or concentration of light rays. Transformation optics is a geometrical technique that allows determining what metamaterial properties reproduce the light path inside a deformed space. This has resulted in impressive and, at the same time, intuitive, material designs such as invisibility devices that hide an object by guiding light rays around it. Thanks to rapidly advancing fabrication methods, metamaterial designs may result in a variety of novel properties, such as reconfigurable, two-dimensional, or quantum properties. In the first part of her thesis, Sophie Viaene introduces new concepts to describe reconfigurable metamaterials with properties that are controlled by an external signal. For example, she has developed a consistent description of materials that implement vector potentials for photons to enhance optical forces, and she has discovered that reconfigurable metamaterials are subject to a fundamental speed limit. These findings are important because they point out that active photonic switches can only be improved up to a certain point by making use of metamaterial structures. In the second part of her thesis, Sophie extends the geometrical tools of transformation optics to improve on the understanding of two-dimensional metamaterials and quantum metamaterials. This has allowed designing metamaterial layers that guide light along their surface and has provided new insights into the behaviour of light sources inside metamaterial black holes, which impose a gravitational wave vector shift. By describing advanced electromagnetic phenomena inside reconfigurable, two-dimensional, and quantum metamaterials in an intuitive way, this thesis has contributed to advanced material designs that may be useful in future light-based applications.