Designing metagratings with constant primary diffraction angles across variable refractive indices via particle swarm optimization

Metagratings, a type of metasurface, exhibit various diffraction effects that are influenced by the background refractive index. In this paper, we propose a metagrating that maintains a constant primary diffraction angle across different indices. Utilizing the particle swarm optimization (PSO) algorithm, we designed a metagrating with a primary diffraction angle of 68° in both air and water, achieving efficiencies of 70% and 61.5%, respectively. Numerical simulations confirm its robust diffractive properties regardless of the background environment. This study introduces a novel, to the best of our knowledge, methodology for designing optical components suitable for diverse media, with potential applications in beam deflection, imaging, and detection.