Topology Optimization Enables Freeform Matrix Fourier Optics

Abstract Metasurfaces have revolutionized optics by manipulating light through minute structural modifications, enhancing design flexibility, and reducing conventional optical component size. However, traditional forward design methods often struggle with errors in phase‐structure conversion. Inverse design methods, such as topology optimization, directly optimize the structure for desired phase distributions, allowing for almost arbitrary shapes. In this research, a forward design approach is combined with inverse design topology optimization to realize matrix Fourier optics, creating a single‐layered metasurface that diffracts incident light of various polarizations to specific positions in the far field, fabricated via atomic layer deposition. It is aimed to optimize diffraction efficiency for each polarization using the adjoint method and gradient descent‐based topology optimization, achieving significant improvements in simulations and experiments. The freeform metasurface successfully processed six mixed polarizations, aligning with the matrix Fourier optics concept, demonstrating a polarization contrast of up to 94.4% in numerical and 98.7% in experimental results. Future applications of such polarization‐selective gratings can enhance polarization analysis while reducing component size and improving convenience.