Large-Scale Parametrized Metasurface Design Using Adjoint Optimization

Optical metasurfaces are planar arrangements of subwavelength meta-atoms that implement a wide range of transformations on incident light. The design of efficient metasurfaces requires that the responses of and interactions among meta-atoms are accurately modeled. Conventionally, each meta-atom's response is approximated by that of a meta-atom located in a periodic array. Although this approximation is accurate for metastructures with slowly varying meta-atoms, it does not accurately model the complex interactions among meta-atoms in more rapidly varying metasurfaces. Optimization-based design techniques that rely on full-wave simulations mitigate this problem but thus far have been mostly applied to topology optimization of small metasurfaces. Here, we describe an adjoint-optimization-based design technique that uses parametrized meta-atoms. Our technique has a lower computational cost than topology optimization approaches, enabling the design of large-scale metasurfaces that can be readily fabricated. As proof of concept, we present the design and experimental demonstration of high numerical aperture metalenses with significantly higher efficiencies than their conventionally designed counterparts.

Automated summary

Optical metasurfaces are planar structures made up of subwavelength meta-atoms that can manipulate incident light in various ways. Efficient design of metasurfaces requires accurate modeling of the responses and interactions among the meta-atoms. Traditional methods approximate the response of each meta-atom based on a meta-atom in a periodic array, which is accurate for slowly varying metastructures but not for rapidly changing metasurfaces where complex interactions among meta-atoms occur.