Liquid-crystal diffraction gratings using polarization holography alignment techniques

TLDR

The study demonstrates a polarization holography exposure technique for patterning liquid‑crystal alignment layers on a linear photopolymerizable polymer. The authors analyze the configuration’s structure and switching behavior, and present a simple phenomenological model of the Freedericksz transition for the registered planar‑periodic boundary condition. Three polarization‑grating configurations were realized—true polarization gratings, mixed planar‑periodic/uniform or homeotropic boundaries, and two‑dimensional orthogonal gratings—along with passive gratings achieved using reactive mesogens.

Abstract

A method of patterning surfaces for liquid-crystal alignment using a polarization holography exposure on a linear photopolymerizable polymer alignment layer is demonstrated. Three configurations are demonstrated which include registered planar-periodic surface boundary conditions on both surfaces (true polarization gratings), planar-periodic and uniform planary surface boundary conditions, and planar-periodic and homeotropic boundary conditions. Two-dimensional polarization gratings are also demonstrated by orientating planar-periodic alignment layers orthogonally. Passive polarization gratings are also demonstrated using reactive mesogens to capture the periodic order indefinitely. The underlying structure of the configuration is discussed, including the nature of their switching transition (threshold or thresholdless), for all three configurations. A simple phenomenological model is presented to describe the Freedericksz transition for the registered planar-periodic boundary condition case.