Electrically Reconfigurable Illumination-Engineering Metalens Enabling Quasi-Dark-Field Biological Imaging.

Abstract

Metasurface-based optical image processing has enabled compact and low-power platforms, yet wavefront-differentiation-based metasurfaces remain fundamentally constrained by their reliance on coherent illumination and intrinsically static optical responses. Meanwhile, conventional optical microscopes rely on bulky, mechanically actuated condensers to engineer illumination numerical aperture (NA), restricting continuous tunability and preventing integration into compact or on-chip imaging systems. These limitations highlight the need for a miniaturized, electrically reconfigurable condenser capable of continuous illumination engineering under incoherent illumination within flat-optics architectures. Here, we demonstrate an electrically reconfigurable illumination-engineering (ERIE)-metalens that embeds a polyaniline (PANI) thin film within a metalens to realize a voltage-programmable condenser, enabling continuous illumination NA control and imaging-mode tuning. Leveraging the exceptional optical contrast modulation of PANI, the ERIE-metalens achieves smooth transitions between bright-field, quasi-dark-field, and dark-field imaging under incoherent light with sub-1 V operation. This continuous illumination engineering enables a quasi-dark-field regime, where transmitted and scattered light coexist in a voltage-programmable ratio, yielding hybrid contrast challenging to achieve with conventional condensers or coherent-dependent metasurfaces. Using the hybrid contrast of the quasi-dark-field, we demonstrate multimodal imaging of biological cells, simultaneously revealing overall cell morphology and fine intracellular details with a single integrated device. Our work highlights illumination engineering as an effective approach in flat optics, positioning the ERIE-metalens as an ultracompact, electrically reconfigurable, and incoherent-light-compatible platform for real-world, multifunctional optical microscopy.