Study of azo dye surface command photoalignment material for photonics applications

We provide detailed quantitative characterization of sulfonic bisazodye SD1 as a photoalignment material for photonics applications. The reversibility of photoalignment was tested for transformations between planar and 90 degrees twist orientation states in a liquid crystal (LC) cell using polarized UV light. No degradation was observed for 100 cycles of transformations. A given twist angle of the LC orientation was obtained in a single step, as well as in a sequence of gradually increasing angles. A hysteresis is revealed in the latter case for planar-twist-planar cycles. The material was used for obtaining patterned orientation of a LC polymer providing similarly good quality photoalignment for UV as well as visible light. High efficiency large area and high spatial frequency optical axis gratings (or, polarization gratings) were demonstrated on a polycarbonate substrate. We show the opportunity of obtaining photoalignment in a multilayer system with single exposure to a polarized light. Finally, we provide evidence of a positive feedback in the dynamics of photoalignment due to the orientational effect of an increasing number of aligned molecules.