Electrically Tunable Geometric-Phase Optical Element with Hybrid Retardation and Subwavelength Pixel Size Enabled by Metasurface-Induced Liquid Crystal Patterning.

In this work, we present an electrically tunable hybrid geometric phase optical element (GPOE) at a telecommunication wavelength with the geometric phase jointly imparted by a liquid crystal (LC) layer and the embedded metasurface. A geometric phase (GP) grating was demonstrated both numerically and experimentally, achieving a voltage-switchable diffraction efficiency ranging from 8% to 56% at 1550 nm. Notably, LC patterning was induced exclusively by the spatially varying metasurface with a metaatom period of 800 nm, enabling the realization of LC-GPOEs with a subwavelength pixel size. Furthermore, the metasurface can be purposely designed to provide dynamic light modulation by leveraging LC-mediated resonance tuning of the metasurface, which paves the way for advanced optoelectronic devices. In this work, a halfwave condition was realized through the propagation phase and the resonance phase, which were provided by the LC and metasurface, respectively. As a result, the LC-GPOEs can be made very thin compared with conventional LC-GPOEs. Eventually, the proposed device was able to work with a switching frequency exceeding 110 Hz.