Anapole States and Toroidal Multipole Excitations in Photonic Metastructures

The study of toroidal moments in isolated scatterers and metastructure configurations has shed new light in the physics of light–matter interaction, and it has provided new ways of engineering the scattering response and radiative losses in both dielectric and plasmonic systems. Powered by advances in nanofabrication, toroidal metasurfaces and anapole particle arrays have demonstrated their potential in application fields, such as sensing, harmonic generation, light emission or photodetection, and tunable filtering. These applications have been enabled by the strong field confinement, low losses, narrow line shapes, and high sensitivity to the surrounding materials, all traits of toroidal modes. It is expected that toroidal metastructures will lead to compact devices with even better performance, whereas their potential can be expanded to more exotic applications, such as strongly coupled plexcitonic systems with giant vacuum Rabi oscillations and electromagnetic sources of propagating doughnut pulses for the study of toroidal physics in matter.