Inverse design broadband achromatic metasurfaces for longwave infrared

Meta-optics has witnessed substantial advancements in recent years. Nevertheless, conventional forward design methodologies are encountering difficulties in the face of escalating demands for functional complexity. Inverse design aims to optimize meta-optical designs, but currently limited to expensive and powerful numerical solvers, it is mainly applied to simple functions devices, and is experimentally difficult to implement. In this paper, we put forth a generalized inverse design framework that facilitates the design of aperiodic complex functional meta-optics. The framework, consisting of a high-performance forward simulator model and a global optimization model, achieves system-level objective optimization. We design and implement a Long-Wave Infrared (LWIR) broadband achromatic metalens. The numerical findings indicate that the chromatic aberration is effectively rectified within the operational wavelength range of 8.6-11.4 mu m, exhibiting a maximum focal length deviation percentage of 5.88 %. Moreover, the actual Numerical Aperture (NA) of the proposed LWIR broadband achromatic metalens attains a value of 0.54. The design of this broadband achromatic metalens is anticipated to have significant utility in the domain of LWIR integrated optical systems.