Optical control of the rotation of cholesteric liquid crystal gratings.

Two photoalignment-based methods to achieve orientational control of optical diffractions by cholesteric liquid crystal (CLC) fingerprint gratings are proposed and demonstrated. A trace of methyl red in the CLC host can effectively induce surface alignment upon linearly polarized green exposure and enable optically rewritable alignment. An effective rotation of the photo-aligned CLC grating is attained by changing the surface alignment axis. Using axially symmetric photoalignment, electrically tunable radial and concentric gratings are also realized. 1D grating diffraction is produced by operating off-axis and can be rotated by mechanically moving the axially symmetric grating. Such optical gratings have great potential for practical use in vibration detection, multi-directional optical modulations, and beam steering.