Monolithic Hybrid Metalens Singlet for Broadband Aberration-Corrected LWIR Imaging

Conventional infrared objectives typically rely on multiple refractive elements; however, their size, mass, and assembly complexity limit compact, cost constrained LWIR applications. Here we report a high-transmittance monolithic hybrid metalens singlet for broadband LWIR (8–12 μm) imaging, in which a plano-convex refractive surface and a dispersion-engineered metalens are integrated on opposing optical surfaces. Using subwavelength meta-units selected by an RMS phase criterion evaluated at multiple wavelengths, the singlet simultaneously corrects chromatic and spherical aberrations, achieves near diffraction-limited focusing, maintains back focal length variation within ±40 μm across 8–12 μm, and delivers a broadband MTF close to the diffraction limit. FTIR and system tests show in-band average transmittance of 83.2% (metalens) and 74.8% (complete singlet). The device enables clear thermal imaging of real scenes from 0.8 to 50 m. Owing to its compact form factor and scalable fabrication potential, the monolithic singlet provides a cost-effective building block for lightweight LWIR modules and can be further combined with simple refractive correctors to realize systems with a wider field of view.