Abstract
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.