Abstract
Photoalignment of liquid crystals by using azo dye molecules is a commonly proposed alternative to traditional rubbing alignment methods. Photoalignment mechanism can be well described in terms of rotational diffusion of azo dye molecules exposed by ultraviolet polarized light. A specific feature of the irradiated light is the intensity dependent change of azimuthal anchoring of liquid crystals. While there are various mechanisms of azo dye photoalignment, photo-reorientation occurs when dye molecules orient themselves perpendicular to the polarization of incident light. In this review, we describe both recent achievements in applications of photoaligned liquid crystal cells and its simulation. A variety of display and photonic devices with azo dye aligned nematic and ferroelectric liquid crystals are presented: q-plates, optically rewritable flexible e-paper (monochromatic and color), and Dammann gratings. Some theoretical aspects of the alignment process and display simulation are also considered.
Highlights
The range of potential applications of photoalignment can be extended to many photonic devices and display technologies
We focus on liquid crystals (LCs) polarization converters and the corresponding vector-photoaligned q-plates, which are suitable for arbitrary Vector beams (VBs) generation [21]
The key to successful manipulation of optical properties of LC layer is the control of anchoring energy and the ability to create complex and precise patterns
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The anchoring energy comprises two contributions, which are related to the director tilt in the azimuthal plane (azimuthal anchoring energy, W φ ) and the tilt in the polar plane (polar anchoring energy, W θ ) As it turned out, W φ can be controlled by polarized ultraviolet light if one of the substrates is spin-coated by azo dye [5]. Photoalignment technology provides effective control of main anchoring parameters: easy alignment axis, pretilt angle, and anchoring energy [14]. Elimination of undesired defects enables researchers to develop advanced photonic applications of liquid crystals, which are impossible with the rubbing technique. The range of potential applications of photoalignment can be extended to many photonic devices and display technologies.
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