Time‐Varying Active Flat Optics Driven by a Constant Light Stimulus

ABSTRACT Flat optics compresses bulky optical functions into structured ultrathin layers, and making such components active—able to change their optical response after fabrication—underpins dynamic holography, beam steering, and optical information processing. However, active flat‐optical elements generally require a time‐varying external control signal to produce a time‐varying optical output, so the temporal degree of freedom must be supplied and sustained externally. Here, a photoresponsive chiral liquid crystal is shown to supply this degree of freedom intrinsically, with a single constant light stimulus driving self‐paced, time‐varying optical operation. Pancharatnam‐Berry patterning of the in‐plane director fixes the spatial wavefront, while hybrid planar‐homeotropic anchoring enables continuous through‐thickness helix reconfiguration. As a result, the conversion efficiency of the pre‐encoded geometric‐phase wavefront oscillates over multiple cycles while the spatial diffraction pattern is preserved, and a layered Jones‐matrix model links the evolving helical pitch to the measured response. Correlated fingerprint‐texture and far‐field dynamics track this evolution, and green light optically reverses the response. Such self‐paced modulation is demonstrated across five geometric‐phase elements, spanning beam deflection, vortex generation, axicon, off‐axis imaging, and holographic reconstruction, establishing a transmissive, electrode‐free route to time‐varying active flat optics.