Light Reconfigurable Topological Optical Phase Structure Enabled by a Photoresponsive Chiral System.

The ability to establish significant phase modulation at low applied field provides a promising route toward polarization control and wavefront shaping for liquid‐crystal‐based devices. Owing to the polarization‐selective reflectivity of chiral liquid crystals (CLCs), reflective wavefront shaping via geometric phase is demonstrated when a circularly polarized light is Bragg reflected by a spatially orientated chiral layer. Nowadays, photoresponsive CLCs have attracted extensive attention due to their exotic feature that endows the CLC devices with the capability of electric‐free remote control. Despite the mature photoresponsive CLC materials and the sophisticated reflective geometric phase devices, a light‐induced topological optical phase modulation for a transmissive wave exiting a CLC cell remains elusive. Here, with the employment of a photosensitive chiral dopant, a hybrid aligned photoresponsive CLC system, demonstrating the simultaneous light modulation of topological geometric phase and dynamic phase via helical pitch manipulation is established. The continuous dual‐phase modulation engenders a smooth optically controllable diffraction efficiency (i.e., from <5% to >90%) of the proposed light‐reconfigurable CLC geometric phase optical element prototypes with multistable diffractive behavior, thus launching a paradigm shift for the application of novel liquid‐crystal photonic devices in the field of all‐optical polarization and spin processing. [ABSTRACT FROM AUTHOR]