Simple method of formation of switchable liquid crystal gratings by introducing periodic photoalignment pattern into liquid crystal cell

We have developed a method for the generation of grating structures in nematic liquid crystals that is a modification of the technique described in [Ph.J. Bos, J.C. Chen, D.L. Johnson, W.E. Glenn, C.E. Holton, B.E. Smith, US Patent 5 825 448, October 20, 1998]. Exploiting UV photoalignment as an alignment technique and an amplitude mask, we introduced a periodical variation of the alignment direction into one of the liquid crystal cell surfaces, while the other surface was aligned uniformly. This significantly simplified the process of grating structure formation and allowed for the generation of polarization independent and electrically controllable gratings. It was found that the grating with a period of 86 pm made using this method demonstrated diffraction efficiency of about 30% in the first diffraction order for a thin grating configuration, and the diffraction signal could be suppressed by more than 20 dB by applying electric field across the cell. Using the edge gradient method we found that a spatial resolution limit of the method was as low as 1.1 mu m. This indicates a potential for the proposed method to create periodical structures with a period of about 1 mu m. (c) 2006 Elsevier B.V. All rights reserved.