Dynamic pattern formation and beam-steering characteristics of cholesteric gratings

The dynamic pattern formation and the beam-steering characteristics of cholesteric gratings were studied. Films with a planar cholesteric texture and various thickness to pitch length ratios (d/p) were fabricated. An optical microscope was used to observe the stripe patterns of the cholesteric gratings formed by applying a voltage to the planar films. The micrographs showed that the cholesteric gratings were formed in two different ways, depending on the sample's d/p ratio. For samples with 1/2 less than or equal to d/p less than or equal to 1.0, the grating stripes simultaneously appeared across the whole sample, and the contrast of the stripes increased with time during formation. For films with d/p greater than or equal to 1.5, the stripes were initiated near the edges, and near the defects on the substrates, and then slowly extended to the whole sample along the rubbing direction. The diffraction measurements showed that the diffracted beams could be steered either electrically or optically only for the latter type of film. These results can be well explained theoretically.