Design and Optimization of a Broadband Achromatic Metalens in the Mid-Wavelength Infrared

With the rapid development of metasurfaces, the chromatic dispersion of metalenses has become a major obstacle, as their strong dispersion and narrow bandwidth significantly limit imaging applications. In this work, we present the design of an achromatic metalens operating in the mid-wave infrared (MWIR) band from 3.7 μm to 4.8 μm, based on transmission-phase manipulation. To achieve broadband achromatic focusing, a particle swarm optimization (PSO) algorithm was employed to optimize the dispersion correction term. Furthermore, a library of cylindrical nanostructures made of chalcogenide glass was constructed using full-wave finite-difference time-domain (FDTD) simulations, enabling precise control of both transmission and phase at multiple wavelengths. By relying solely on the intrinsic material dispersion compensation mechanism, the proposed metalens achieves effective chromatic aberration correction across the MWIR band. Simulation results verify enhanced multi-wavelength focusing performance, demonstrating the feasibility of this design for high-resolution, broadband infrared imaging.