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 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.