Discrete Axial Symmetry Accelerated Inverse Design for LWIR Large-diameter Metalenses

Designing and simulating large-diameter metalenses for the long-wave infrared (LWIR) range is challenging due to the high computational resource demand. To overcome this, we propose a scalable 3D Finite-Difference Time-Domain (FDTD) inverse design strategy that exploits axial symmetry, enabling the development of advanced large-aperture metalenses for LWIR. This approach features discrete axial symmetry with radially and azimuthally fractured domain decomposition schemes, facilitating fast and accurate simulations and optimizations of large-area, freeform, broadband dispersion-engineered LWIR metalenses. By adapting Maxwell’s equations to polar coordinates and introducing innovative symmetry reduction and domain decomposition methods, we aim to not only achieve significant reductions in computational costs but also unlock new design possibilities for LWIR metalenses. GPU and MPI accelerations as well as a graphic user interface of our FDTD code will be implemented. Our design process incorporates adjoint method and dispersion engineering principles to design freeform and topology-optimized structures that maintain high focusing efficiency over a wide bandwidth (8-12 µm). Our goal is to design and simulate an LWIR metalens with at least a 5 cm x 5 cm physical aperture, a numerical aperture of 0.25, and at least 95% average focusing efficiency across the broadband range. These large-aperture metalenses, once designed, will be fabricated using deep-ultraviolet lithography and rigorously tested to assess their performance against that of commercial counterparts. The metalenses will be mounted in a customized housing together with LWIR sensors.