Abstract

We demonstrate an electrically tunable dual-mode metalens capable of polarization-sensitive focal control, combining high-resolution imaging and depth-sensing functionalities into a single compact device. By integrating hydrogenated amorphous silicon (a-Si:H) meta-atoms with a liquid crystal (LC) modulator, the proposed metasurface independently manipulates left- and right-circularly polarized (LCP/RCP) incident light, generating a rotating double-helix focal distribution for LCP and an extended depth-of-focus (DOF) for RCP illumination.

The meta-atoms were rigorously optimized using propagation and geometric phases, enabling precise phase control and high transmittance at a wavelength of 635 nm. Experimental characterization confirmed near-diffraction-limited lateral and axial resolutions, closely aligning with theoretical predictions. The integrated LC cell facilitates milliseconds polarizationswitching between depth-sensitive double-helix and high-resolution DOF imaging modes. We further verified depth-extraction capabilities by analyzing rotation angles from dual-image focal spots under mixed-polarization illumination.

Depth-resolved imaging of a rubber-tree leaf, a skeletal-muscle cross-section, and a live planarian retrieved color-coded depths, demonstrating the effectiveness on complex biological tissues. This polarization-driven, electrically tunable metalens thus provides a versatile and effective optical platform suitable for advanced applications in biomedical imaging, three-dimensional sensing, adaptive optics, and compact imaging systems.