  Advanced photonic nanostructures have enabled the maximization of synthetic
chiroptic activities. The unique structuring of these building blocks has
empowered chiral selective interactions with electromagnetic waves in plasmonic
structures and dielectric media. Given the repertoire of optimized chiral
surfaces in the literature and the ubiquity of chirality in the organic realm,
the natural direction to consider is the operation of these devices in larger
optical systems much like their chiral organic counterparts. In this review, we
recapitulate advances in active and nonlinear chiral metamaterials. Many of the
results, such as the magneto-chiral anisotropy and third-harmonic Rayleigh
scattering optical activity, are relatively unknown members of the more
conventional family of tuning methodology and nonlinear processes. We believe
they are poised to play an instrumental role in designing advanced chiroptic
systems for applications in biochemistry, valleytronics, spintronics, and
chiral quantum optics.
