Freeform nonlocal metasurfaces enabled by tailored optical nearfields

The tailoring of light-matter interactions between free-space waves and resonant modes has been extensively studied to engineer the far-field optical responses of metasurfaces. To date, most metasurface design paradigms focus on engineering far-field properties based on physical intuition and numerical experiments. A pathway to enable direct, customized optical modes remains elusive due to the lack of precise analytical correlations between geometry and near-fields. In this study, we propose a novel computational framework for realizing freeform non-local metasurfaces based on the explicit design of optical modes with customized resonant properties. Utilizing this method, we demonstrate ultra-thin nonlocal metasurfaces supporting multifunctional, high-quality-factor responses. We further extend the capability to enable planar chiral metasurfaces with large near-field chirality.