  Metasurfaces consisting of hybrid metal/dielectric nanostructures carry
advantages of both material platforms. The hybrid structures can not only
tightly confine subwavelength electromagnetic fields but also lower the
absorption losses. Such optical characteristics are difficult to realize in
metamaterials with only metal or dielectric structures. Hybrid designs also
expand the scope of material choices and the types of optical modes that can be
excited in a metasurface, thereby allowing novel light matter interactions.
Here we present a metallo-dielectric hybrid metasurface design consisting of a
high-index dielectric (silicon) nanodisk array on top of a metal layer
(aluminium) separated by a buffer oxide (silica) layer. The dimensions of the
nanodisks are tuned to support anapole states and the period of the nanodisk
array is designed to excite surface plasmon polariton (SPP) at the metal-buffer
oxide interface. The physical dimensions of the Si nanodisk and the array
periods are optimized to excite the anapole and the SPP at normal incidence of
light in the visible-NIR (400-900 nm) wavelength range. Finite difference time
domain (FDTD) simulations show that, when the nanodisk grating is placed at a
specific height (~200 nm) from the metal surface, the two modes strongly couple
at zero detuning of the resonances. The strong coupling is evident from the
avoided crossing of the modes observed in the reflectance spectra and in the
spectral profile of light absorption inside the Si nanodisk. A vacuum Rabi
splitting of up to ~ 129 meV is achievable by optimizing the diameters of Si
nanodisk and the nanodisk array grating period. The proposed metasurface design
is promising to realize open cavity strongly coupled optical systems operating
at room temperatures.
