Extreme Field Confinement in All-Dielectric Metasurface Cavities

Bound states in the continuum enable extreme confinement of electromagnetic energy in structures otherwise open to incoming waves. In recent years, they have been demonstrated in various photonic systems and single resonators. Presently, we investigate Fabry-Pérot resonances in a planar cavity consisting of two all-dielectric metasurfaces. The metasurfaces are characterized by their effective magnetic and electric surface impedances enabling an analytical approach. The resonance conditions are derived and two cavity designs comprised of metasurfaces of all-dielectric spheres are investigated. The analytical and numerical results obtained for the two designs are compared showing excellent agreement, with quality factors of ~ 1700 and ~ 6500, respectively. Furthermore, we show that the proposed approach can be extended to other geometries, presenting a design for a cylindrical cavity enclosed in a concentric metasurface with quality factor ~17000. The proposed metasurface cavity may be of interest for the design of filters, antennas, sensors, and nonlinear systems.