Unconventional Nonlinear Metaphotonics

ABSTRACT Nonlinear optics plays a pivotal role in many modern photonic technologies, enabling frequency conversion, ultrafast signal processing, and quantum light generation. Recent advances in plasmonics, metamaterials, and metasurfaces provide unprecedented control over electromagnetic fields at the nanoscale, thus significantly enhancing light–matter interaction. These recent developments open new avenues for the study of nonlinear optical phenomena in resonant photonic structures that transcend conventional paradigms. In this Perspective , we explore several emerging directions in nonlinear optics of metastructures, unified by the general title of “unconventional nonlinear metaphotonics.” More specifically, we focus on the recent demonstrations of magnetic‐dipole‐enhanced second‐harmonic generation in plasmonic structures, nonlinearity‐induced nonreciprocal effects with metasurfaces, unconventional power scaling of the generated optical harmonics in resonant nonlinear metasurfaces, and also high‐harmonic generation observed in high‐ nonlinear metasurfaces.