Electrically tunable lens based on a dual-frequency nematic liquid crystal.

We report on an electrically controlled liquid-crystal-based variable optical lens filled with a dual-frequency nematic material. The lens design employs a hole-patterned electrode structure in a flat nematic cell. In order to decrease the lens switching time we maximize the dielectric torque by using a dual-frequency nematic material that is aligned at an angle approximately 45 degrees with respect to the bounding plates by obliquely deposited SiO(x), and by using an overdrive scheme of electrical switching. Depending on the frequency of the applied field, the director realigns either toward the homeotropic state (perpendicular to the substrates) or toward the planar state (parallel to the substrates), which allows one to control not only the absolute value of the focal length but also its sign. Optical performance of the liquid-crystal lens is close to that of an ideal thin lens.