Liquid crystal diffraction gratings using photocrosslinkable liquid crystalline polymer films as alignment layers

Abstract

We report liquid crystal (LC) diffraction gratings fabricated using photocrosslinkable liquid crystalline polymer (PLCP) films for alignment layers of low-molecular-weight nematic LCs. In our PLCP films, the mesogenic molecules were oriented axis-selectively by irradiating them with linearly polarized (LP) ultraviolet (UV) light followed by annealing at the LC temperature. The optical anisotropy caused by the molecular orientation was relatively high. The orientation direction was controlled by the exposure energy of LP UV light and the polarization direction. PLCP films are transparent in the visible region of the spectrum and are thermally stable. This means that they are suitable for various optical applications. PLCP films with uniaxial alignment are applicable for use as alignment layers for low-molecular-weight LCs. Using PLCP films with a periodic orientation distribution, we can fabricate LC diffraction gratings that have high diffraction efficiencies, various polarization conversions, and can be switched with the application of external fields. We will then summarize our recent studies on photoalignment techniques of PLCP films and LC diffraction gratings with photoregulated PLCP films.