Bright-Field and Edge-Enhanced Imaging Using an Electrically Tunable Dual-Mode Metalens

The imaging of microscopic biological samples faces numerousdifficultiesdue to their small feature sizes and low-amplitude contrast. Metalenseshave shown great promise in bioimaging as they have access to thecomplete complex information, which, alongside their extremely smalland compact footprint and potential to integrate multiple functionalitiesinto a single device, allow for miniaturized microscopy with exceptionalfeatures. Here, we design and experimentally realize a dual-mode metalensintegrated with a liquid crystal cell that can be electrically switchedbetween bright-field and edge-enhanced imaging on the millisecondscale. We combine the concepts of geometric and propagation phase to design the dual-mode metalens and physically encode the requiredphase profiles using hydrogenated amorphous silicon for operationat visible wavelengths. The two distinct metalens phase profiles include(1) a conventional hyperbolic metalens for bright-field imaging and(2) a spiral metalens with a topological charge of +1 for edge-enhancedimaging. We demonstrate the focusing and vortex generation abilityof the metalens under different states of circular polarization andprove its use for biological imaging. This work proves a method for in vivo observation and monitoring of the cell responseand drug screening within a compact form factor.