Resonant leaky modes in all-dielectric metasystems: Fundamentals and applications

All-dielectric metamaterials and metasurfaces have been demonstrated as ideal platforms to manipulate electromagnetic waves and enhance light–matter interaction. Analogous to guided modes in a dielectric waveguide, high refractive index dielectric metasurface supports leaky modes (also known as quasi-normal modes), including electric and magnetic resonant modes, which are represented by a complex eigenfrequency. Such leaky modes play a dominant role in governing the optical properties of dielectric nanoparticles and metasurfaces (i.e., absorption, scattering and emission). These unique properties enable researchers to design dielectric metasurfaces with desired functionalities without resorting to computationally expensive parameter scanning with full-wave simulation. Moreover, leaky modes underpin many exciting topics, such as Fano resonances, bound states in the continuum (leaky modes with Q=+∞), coherent perfect absorption, parity-time symmetry, and exceptional points. This review provides an overview of the recent progress on leaky modes of all-dielectric-based metasystem, from fundamental physics to their applications. We start with surveying the fundamental physics of leaky modes and discussing leaky mode engineering in either a passive or active way. Then, we discuss the recent progress on the leaky modes’ application in the perfect light absorber, solar cells, photodetectors, enhanced light emission and lasing, strong coupling, enhanced nonlinear harmonic generation, and structural color. Next, we present an overview of recent advances in bound states in the continuum and their application in enhanced light–matter​ interactions. Also, we review other interesting topics: parity-time symmetry and exceptional points, and discuss their application in manipulating light in an unprecedented way. Finally, we present our vision of the challenges and opportunities in this rapidly developing field of research.