Ultra-Spatiotemporal Light Confinement in Dielectric Nanocavity Metasurfaces

TL;DR

This paper introduces a dielectric nanocavity metasurface with ultra-high quality factor and tiny mode volume, enabling extreme light confinement and enhanced light-matter interactions in free space.

Contribution

It proposes a novel quasi-bound state in the continuum cavity in dielectric metasurfaces with unprecedented confinement properties.

Findings

Achieved Q factor of ~10^6 in dielectric nanocavities.

Realized ultra-small mode volume of ~10^{-2} (λ/n)^3.

Demonstrated potential for enhanced Purcell effect and strong coupling.

Abstract

Light concentration with strong temporal and spatial confinement is crucial for tailoring light-matter interaction. Electromagnetic cavity modes in photonic and plasmonic resonators provide platforms for optical field localization. Here, we propose a concept of quasi-bound states in the continuum gap cavity and reveal that ultra spatiotemporal confinements in free-space can be realized in a dielectric nanocavity metasurface. By introducing an asymmetric air slot in a nanodisk resonator, an ultra-high quality factor $\rm Q \sim 10^6$, accompanying an ultra-small effective mode volume, $\rm V_m \sim 10^{-2}$ $(\lambda/n)^3$ are achieved resulting in a Purcell factor of $\rm 10^6 (\lambda/n)^{-3}$ in the visible wavelength range. The toroidal dipole drives the electric and magnetic field concentration in the air gap with a generated vortex polarizing electric field. As an alternative to plasmonic and photonic crystal cavities, our study provides a more intriguing platform for engineering light-matter interaction to advance a plethora of fundamental studies and device applications, such as Purcell factor enhancement, room temperature strong coupling and nonlinear nanophotoncis.