Two-Dimensional Liquid-Crystal Photoalignment by Multiple Illumination Steps

Photoalignment can define the average liquid-crystal (LC) orientation when a photosensitive material is illuminated with linearly polarized light. For azo-based materials, the alignment is perpendicular to the direction of the linear polarization for sufficiently high illumination doses. The defined orientation can be overwritten by a second illumination step with a different polarization. In general, the resulting alignment is a function of the detailed illumination procedure. In this work, a method is presented to model the LC director alignment as a function of an illumination procedure consisting of three steps in which the first and third steps have spatially rotating linear polarization, while the second step uses circularly polarized light. The model is used to simulate the optical transmission between crossed polarizers in order to verify experimental observations of a device with a two-dimensional orientation pattern. Because photoalignment can realize complex alignment patterns with high resolution for diffractive optical components, it is attracting increasing interest in the field of augmented reality displays.