25.2 Extreme Wave-Based Metastructures.

In recent years, the field of metamaterials and metasurfaces has provided exciting opportunities for unprecedented control of electromagnetic and optical signals with numerous applications. In order to sculpt and manipulate waves to achieve exciting functionalities, we need materials. Judiciously engineered metamaterials and their two dimensional versions, i.e., metasurfaces, which are interfacial structures formed by properly designed and arranged scattering elements, are useful platforms to achieve extreme control of waves leading to wave-based functional devices and components. Numerous paradigms and platforms have been introduced and explored in this context in recent years. These include optical analog computing machines, metamaterial photonic processors, near-zero-index photonics, four-dimensional metamaterials, and optical lumped nanocircuits, just to name a few. In the following, a subset of such extreme metastructures is briefly reviewed.