Fresnel Lenses in 90° Twisted-Nematic Liquid Crystals With Optical and Electrical Controllability

This letter presents an optically and electrically controllable Fresnel lens in a 90° twisted-nematic liquid crystal (LC) cell with a photoconductive polymer layer. A dc voltage was applied to the cell irradiated using an interference pattern obtained from a Sagnac interferometer. The dc electric field caused the accumulation of ionic impurities on the substrates, thereby reducing the strength of the electric field in the cell. Light illumination caused an increase in the conductivity of the photoconductive layer, increasing the electric field in the bright zones of the interference pattern. The difference in the electric fields in the bright and dark zones led to discrepancies in the reorientation of the LC, allowing it to be tuned by adjusting the intensity of the Fresnel pattern and the applied dc voltage.