6. Chiral Metamaterials and Metadevices

Chiral metamaterials generally consist of arrays of planar metallic or dielectric gammadions on a substrate, where, if linearly polarized electromagnetic wave such as GHz, THz, or visible light is incident on the array, it becomes elliptically polarized upon interaction with the gammadions with the same handedness as the gammadion itself. While the conventional metamaterials require negative permittivity and permeability simultaneously to achieve negative refraction, chiral metamaterials offer an alternative and simpler route to realize negative refraction with a strong chirality while neither negative permittivity nor permeability is required. Furthermore, in combination with strong resonances, optical tuning, and hyperbolicity, chirality can lead to a new route to negative refraction, switchable chirality, photonic topological insulators, and other chiral metadevices. In addition, fabricate approaches such as chiral top-down, bottom-up, direct laser writing, 3D printing, and block copolymer self-assembly methods have been explored for forming various chiral metamaterials. Nevertheless, a combination of smart designs and material property control methods such as (quantum) gain and nonlinearities will be needed for providing a new foundation for many practical applications of chirality. This chapter will briefly review the developments on chiral metamaterials, including fundamental principles, various chiral metamaterials realized by different nanofabrication approaches, and the applications and future prospects of this emerging field.