New Simple Model of a Liquid Crystal Light Valve

Abstract

The device described consists of two transparent electrodes (an In2O3 film and a conducting glass electrode) and between them a photosensitive element in series with a liquid crystal. It does not require an optical blocking layer to protect the photosensitive material from the “readout” light”. It is based on the electric field induced cholesteric-nematic phase transition. The photosensitive element is an indium oxide (In2O3)/silicon heterojunction. A 13 μm thick layer of a mixture of 1132 TNC Merck nematic product (92%) + cholesteryl nonanoate (8%) is sandwiched between the silicon wafer (10 000 Ω·cm) and the conducting glass electrode. An ac voltage is applied between the In2O3 film and the conducting glass electrode. When the In2O3 side is illuminated with the “writing light”, the diode impedance decreases and the electric field in the liquid crystal increases becoming sufficient to produce the cholesteric-nematic transition. The applied voltage necessary to induce this transition has been found to decrease for a given frequency when the writing light power PWr increases and to be independent of PWr for its higher values. With a convenient choice of the cell voltage, a sensitivity better than 10 μW·cm-2 can be easily obtained. The sensitivity is maximum for a writing light wavelength of 0.8 μm, therefore such a structure can be used in the near infrared. Rise times of a few tens of ms can be obtained.KeywordsLiquid CrystalSilicon WaferCell VoltageLight WavelengthIndium OxideThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.