Geometry-invariant optical properties of dielectric meta-atoms with antireflection coatings

High-index dielectric meta-atoms enable high-efficiency metasurfaces but inherently suffer from reflection losses due to strong refractive-index contrast. While antireflection coatings (ARCs) mitigate these losses, metasurface design is commonly assumed to remain strongly geometry-dependent. Here, we demonstrate the existence of a geometry-invariant regime for dielectric nanorod meta-atoms with ARCs. For Si and InP meta-atoms at visible and infrared wavelengths, we show that the phase, transmission, reflection, and polarization responses are independent of the specific cross-sectional shape, triangular, square, hexagonal, octagonal, or circular, provided that the effective cross-sectional area is conserved and the geometry exhibits C₃ or higher rotational symmetry. This invariance is preserved under monolayer and bilayer ARCs, and the phase shift and polarization responses remain invariant regardless of the presence or absence of coatings. Our results reveal that the optical response can be fundamentally decoupled from the geometric form, redefining design constraints and enabling fabrication-robust metasurface architectures with ARCs.