New types of reflective periodical structures in the material with bulk photoalignment of LC polymer using UV polarization holography

• Published in: Optical materials 2024-08, Vol.154, p.115655, Article 115655
• Main Authors: Sakhno, O., Gritsai, Y., Sahm, H., Wegener, M., Stumpe, J.
• Format: Article
• Language: English
• Subjects: Liquid crystal polymer; Polarization grating; Soft materials; Thin films; UV holography
• ISSN: 0925-3467; 1873-1252
• DOI: 10.1016/j.optmat.2024.115655

Two types of new periodical polarization structures generated by UV polarization holography in thin solid films of LC photosensitive polymer (LCP) due to bulk photo-alignment were experimentally demonstrated. The first type of the structures is similar to cholesteric ones. However, these structures fabricated just by means of optical exposure without chiral dopants. Such technique overcomes some restrictions of alternative known methods of chiral structures fabrications using chiral dopant (e.g., arbitrary orientation of the LC planes). The second type is a new one, which can be realized only using the developed material approach with bulk photo-alignment. This structure is similar to known transmission circular polarization gratings, but the axis is rotated by 90°. The fringes (the planes of equal orientation of LC) in such structures are almost parallel to the layer, and the LC orientation is changing periodically across the layer from in-plane to the perpendicular position. Both new regular periodical structures can be used as volume reflective polarization gratings with several unique properties suitable for the numerous optical applications, including display ones. Specific suggestions for improving the quality of new holographic LC-structures are offered. •Two types of periodical thin-film reflection structures with bulk photo-alignment.•New structures fabricated using a special LC photopolymer and UV polarization holography.•New reflection polarization structures with UV and visible wavelengths.•These diffractive structures can be used as volume reflective polarization gratings.