Adjustable large-area dielectric metasurfaces for near-normal oblique incident excitation

Abstract

We present large-area (25 cm 2 ) dielectric metasurfaces based on silicon photonic crystal slabs. Adjustment of the slab thickness allows to systematically shift the metasurface resonances over several hundreds of nanometers. We compute the three-dimensional field energy density near the surface and determine optimum slab thicknesses for selected near-infrared excitation wavelengths applied in biophotonics. Our simulations reveal up to 17-fold enhanced near-field energy densities at normal incidence, but over 500-fold enhancement at 4° incident excitation. We explain this behaviour via the coupling of external radiation with symmetry-protected bound states in the continuum. These results enable metasurface-enhanced spectroscopy on large areas and underline the benefit of slight oblique incidence excitation conditions.