Large-Aperture Polarization-Independent Broadband Achromatic All-Dielectric Metalens for Terahertz Focusing.

As a promising alternative to conventional lenses, terahertz (THz) achromatic metalenses with planar configurations are of great significance in broadband optical applications. However, as the application scenarios extending to macro-scale far-field optical imaging, an inherent conflict arises between the increasing demand for large-aperture, high focusing efficiency, broadband achromatic metalenses and the steep rise in design complexity and fabrication costs. Herein, a multifunctional achromatic metalenses design scheme is proposed to realize large-aperture, high focusing efficiency, and polarization-insensitive THz all-dielectric single-layer metalenses, by integrating the discrete multi-wavelength achromatic design method and the global optimization algorithm. The designed metalens is successfully fabricated with a diameter up to 2.21 cm, which is the largest reported THz achromatic metalens to our knowledge. Experimental measurement results demonstrate that it has polarization-insensitive characteristics and excellent achromatic focusing performance from 0.80 to 1.20 THz, with achromatic coefficient values below 2.9% and average focusing efficiencies greater than 46% under both x- and y-polarized incident waves. Furthermore, the broadband achromatic imaging performance is characterized and validated, confirming its remarkable achromatic imaging capability. This study not only showcases an outstanding THz achromatic metalens but also presents a generalizable design strategy applicable across the entire electromagnetic spectrum.