Varifocal Meta-Lens for Multifunctional Focusing and Imaging.

Integrating multifunctionality and tunability in beam control is crucial for advanced applications such as adaptive imaging and optical microscopy. However, achieving both capabilities simultaneously in a compact optical system remains challenging, as conventional optics are bulky and typical tunable metasurfaces offer only limited operational modes. Here, polarization-independent varifocal meta-lens is presented, composed of two cascaded metasurfaces, enabling mode switching between a non-diffracting abrupt autofocusing (AAF) beam and a diffraction-limited focusing beam. The mode transition is governed by the dual interpretation of the superimposed phase profile in real space and the spatial frequency domain. A Moiré-based tuning mechanism enables continuous focal length modulation via in-plane rotation. The proposed varifocal meta-lens achieves a focal length tuning range of 10.3 mm in AAF mode (163% tuning ratio) and 29.3 mm in standard focusing mode (345% tuning ratio). The AAF beam maintains a nearly constant spot size throughout its range, while the standard focusing mode supports brightfield imaging with a relative zoom magnification from 1× to 1.95×. This compact platform offers a promising solution for tunable and integrated optical systems.