Submillisecond Inverse TN Bidirectional Field Switching Mode

We demonstrate a new fast electro-optical switching mode in homeotropically-aligned layer of a nematic liquid crystal. The electric field spatial distribution in the LC layer is switched between twisted-planar and normal states by means of driving the electric potentials over a system of interdigitated electrodes, which have mutually orthogonal orientation at the top and bottom sides of the LC layer. A twisted-planar field characterized by twisted spatial distribution induces a twisted state of the LC, whereas switching back to the homeotropic state is driven by a normal field that is oriented along the LC layer normal. The bidirectional driving eliminates the stage of free relaxation to the homeotropic state, thus allowing for very fast electro-optical switching between the optical states: total switching time is less than 1 ms, which is an order faster than for the conventional twist effect in nematics. The advantages of the suggested driving mode include gradual grayscale and deep-black state that is due to initial homeotropic alignment with a zero pretilt angle.