Two-level optimizer for large-scale metasurfaces with strong near-field coupling

We introduce a two-level window-based optimization architecture that enables the inverse-design of metasurfaces containing hundreds of adjustable parameters while accurately modeling near-field coupling effects. Our method contains two nested iterative optimizers and effectively optimizes a 300 unit-cell metalens (aperture diameter of 108 µm) and yields a 73.2% increase in focusing intensity, addressing the established fabrication-performance tradeoff for low aspect-ratio (<3) metasurfaces.