Continuous Varifocal Metalens Based on Phase-Change Material

Abstract: Metasurfaces have provided new opportunities for the realization of flat lenses, among which tunable metalenses have garnered considerable attention due to their flexible functionalities. In this paper, we present a continuously tunable metalens based on the phase-change material Sb${2}$S${3}$, which enables precise and continuous focal length control through the transition of states. Under the excitation of linearly polarized light at 1550 nm, phase compensation is provided by changing the crystallization state of the Sb${2}$S${3}$ nanopillars, allowing the focal length to continuously shift between 36 $\mu$m and 48 $\mu$m. At the same time, the metalens maintains a high focusing efficiency over 75%. This approach provides greater design flexibility and broader applicability across diverse applications. By reducing the reliance on polarized light sources, it enhances device integration and tunability, paving the way for new opportunities in the practical implementation of metalenses in advanced optical imaging and nanophotonics.