Reflective Metalens Architecture for Broadband Achromatic Performance in the LWIR Range

We design a broadband all-dielectric reflective met-alens for the 9.6 − 11.6μm LWIR range, comprising ZnSenanopillars on a Ge/ZnSe DBR. Using dispersion-engineeredphase and group delay control via a spectral offset approach,the metalens achieves diffraction-limited focusing with < 7%focal length frictional change (FLFC). Full-wave simulationsconfirm high reflectivity (> 95%), complete 2π phase coverage,and an average focusing efficiency of ∼ 73%,peaking at 80%. Themethod eliminates the need for global optimization by analyticallyembedding chromatic correction into the phase profile, enablingscalable, high-NA infrared optics suitable for compact imagingsystems.