Millisecond-level electrically switchable metalens for adaptive rotational depth mapping and diffraction-limited imaging
The intrinsic trade-off between depth-of-focus and lateral resolution in conventional optical systems constrains three-dimensional imaging in compact form factors. This work demonstrates an electrically tunable dual-mode metalens that integrates hydrogenated amorphous silicon (a-Si:H) meta-atoms with a liquid crystal (LC) modulator to independently manipulate left- and right-circularly polarized (LCP/RCP) light at 635 nm. Under LCP illumination, the metalens generates a rotating double-helix point spread function (PSF) encoding depth via rotation angle; under RCP illumination, it produces an extended depth-of-focus with a narrow PSF for high-resolution imaging. Propagation and geometric phases were co-optimized via rigorous coupled-wave analysis (RCWA), yielding high transmittance and precise phase control. Experimental characterization confirmed near-diffraction-limited lateral and axial resolutions. The integrated LC cell enables millisecond-scale polarization switching between depth-sensitive and high-resolution modes. Depth extraction was validated by correlating rotation angles of dual-image focal spots under mixed-polarization illumination, with axial displacements of Δz1 = 30.5 μm, Δz2 = 0 μm, and Δz3 = −48.3 μm corresponding to rotation angles β = −25.6°, 0°, and 16.9°, respectively. Depth-resolved imaging of a rubber-tree leaf, skeletal-muscle cross-section, and live planarian retrieved color-coded depth maps, demonstrating efficacy on complex biological tissues. This polarization-driven platform offers a compact solution for biomedical imaging, three-dimensional sensing, and adaptive optics.