Fast beam steering cholesteric diffractive devices

Electrically-controlled diffractive gratings are developed on the basis of cholesteric liquid crystal confined between two transparent non-patterned electrodes. The electrodes are coated with alignment layers providing either planar or homeotropic anchoring. For planar alignment the applied electric field causes reorientation of initial (zero field) planar state and creates one-dimensionally modulated structures in the plane of the cell. The modulations occur via two distinct scenarios: (I) nucleation and expansion of 'stripes' and (II) undulation of quasinematic layers in the plane normal to the cell's plates. The process (II) is faster since it does not require overcoming an energy barrier. In cells with homeotropic surface alignment modulated structures exist without applied voltage. Magnetic field is used to provide uniform orientation of these structures. Confocal microscope studies and 2-D computer simulations are carried out to reveal the fine structure of the diffractive gratings.