Scalable Design and Optimization of Reconfigurable Sb 2 S 3 Metasurfaces

ABSTRACT Phase‐change material (PCM)‐based reconfigurable Huygens metasurfaces offer a promising route toward dynamically programmable flat optics; however, their realization is limited by the lack of scalable and computationally efficient design methodologies. Inter‐element coupling in densely packed arrays renders lookup‐table approaches ineffective, while accurate full‐field FFT‐based methods are computationally prohibitive for large‐area multi‐state devices. Here, we introduce two scalable optimization cost functions—phase‐match and overlap‐integral—that incorporate phase fidelity and power efficiency at the pixel level. The phase‐match method provides a computationally efficient intermediate approach, while the overlap‐integral method enables full‐field optimization of large‐area metasurfaces with arbitrary wavefront transformations. Using Sb 2 S 3 as a low‐loss PCM platform operating at 820 nm, we demonstrate a reconfigurable beam steerer and a reconfigurable cylindrical metalens. The phase‐match method improves amorphous steering efficiency from 15.0% to 36.1%, a 21.1 percentage‐point (141% relative) improvement compared to the manual lookup‐table methods, while maintaining 30.3% crystalline transmission. For the cylindrical metalens, overlap‐integral optimization over multiple pixels enables an improvement in the amorphous‐state focusing efficiency from 32.8% to 48.0%, a 15.2 percentage‐point (46% relative) improvement, while maintaining ∼49% crystalline transmission in the plane‐wave state. These results demonstrate scalable, high‐performance design without full‐aperture simulations, advancing multi‐state flat optics toward practical photonic systems.