Optically and electrically controllable Fresnel lens with 90° twisted nematic liquid crystals
Shih-Hung Lin1, Chien-Yu Li1*, Chie-Tong Kuo1, Hui-Chen Yeh2
1Department of Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan
2Graduate Institute of Electrical Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung, Taiwan
* presenting author:Chien-Yu Li, email:cdebgtmju2002@gmail.com
In this study, we propose a opto-electrically controllable Fresnel lens based on a C60-doped photoconductive layer (PVK) with 90° twisted nematic liquid crystals. The C60/PVK layer is irradiated with a Fresnel-zone-plate (FZP) pattern formed by the Sagnac interferometer, resulting in the different conductivity of PVK between the bright and dark zones of the interference pattern. The difference of effective electric fields in the cell are generated under applied dc voltage, lead to the difference of director distributions of liquid crystals. The cell gap of the Fresnel lens is satisfied the Gooch-Tarry conditions, thus the polarization rotation effect is valid for any incident polarization directions. The first order diffraction efficiency of the Fresnel lens can be optically and electrically controlled by changing the intensity of the FZP pattern and applied dc voltage, respectively.

Keywords: Sagnac interferometer, Fresnel lens, Twisted nematic liquid crystal, Photoconductive film