Recent advances in liquid-crystal polarization volume gratings

Volume Bragg gratings (VBGs) have many applications including filters, wavelength multiplexing devices, and seethrough displays. As a kind of VBGs, polarization volume gratings (PVGs) based on liquid crystal polymer show the advantages of nearly 100% efficiency, large deflection angle and unique polarization selectivity. Previous studies of transmissive and reflective PVGs are based on a planar architecture. In this work, we introduce slanted configuration, i.e. slanted cholesteric liquid crystals. The optical properties of these two different-type PVGs are investigated and compared. Specifically, we emphasize on the diffraction efficiency and polarization state of the diffracted light. Through comparing the experimental results with simulations, the existence of slanted PVGs is validated. We further report a stretchable, flexible, and rollable PVG film with high diffraction efficiency. Previously reported PVGs are of high diffraction efficiency but with fixed diffraction angles. By transferring PVGs onto a flexible and stretchable substrate, the obtained PVG films exhibit high diffraction efficiency, tunable periodicity, and excellent flexibility. The PVG films offer tunable diffraction angles and Bragg reflection bands by mechanical stretching. Stretch-release cycles test is also performed to ensure the mechanical robustness and reliability. This PVG film is especially useful for laser beam steering and augmented reality (AR) waveguide coupler.