An all-dielectric achromatic metalens with high performance in the long-wavelength infrared regime

Over recent decades, metasurfaces have achieved significant advancements in the development of integrated and miniaturized optical devices. A notable area of research within this field is the development of metalenses. In this study, we propose a broadband achromatic metalens that operates across a wide wavelength range from 9.6 μm to 11.6 μm. For the initial metalens, based on the geometric phase principle, micro adjustments are made to the dimensions of individual nanopillars to compensate for phase deviations. To efficiently optimize this metalens, we employ a hierarchical iteration strategy that divides the optimization space into overlapping groups, significantly reducing the loss rate and computational effort. Within each group, an improved reptile search algorithm (IRSA) is proposed to find the optimal solution. This algorithm incorporates a quantum mutation strategy to address the issues of premature convergence and imbalance during its search process. The results indicate that the proposed metalens attains an average focusing efficiency of 39.7% and the correction of chromatic aberration is achieved with a coefficient of variation of only 2.7%. This achievement represents a significant advancement in the field of achromatic metalenses.