Electro-opto controllable aperture for linearly polarized lights using double twisted nematic liquid crystal cells

• Main Authors: Jia-Hau Li, 李家豪
• Other Authors: Ko-Ting Cheng
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/89b49x

碩士 === 國立中央大學 === 光電科學與工程學系 === 106 === In this study, the poly(9-vinylcarbazole) (PVK) was adopted to be the planar alignment layer for a twisted nematic liquid crystal (TNLC) cell. Combing the photoconductive property of PVK and the polarization rotation property of TNLC, the fabricated TNLC cell can be applied as an electro-opto controllable LC aperture for linear polarized lights. The electrical control by an applied DC voltage and the optical control by a UV light illumination make the controllable aperture size of the ring-like aperture (normally white state) and the spot-like aperture (normally black state). The controllable range of aperture diameter is based on the spot size of UV light. In addition to the demonstration of LC aperture by a single layer 90˚-TNLC, this study also proposes that the combined two 45˚-TNLC cells, also known as a tandem 90˚-TNLC, can improve the performances of the electro-opto controllable LC aperture. The basic concept of the tandem 90˚-TNLC is the self-compensation of the undesirable phase retardation. Hence, the degree of linear polarization (DoLP) value of the output beam and the transmittance after passing through an analyzer can be significantly improved. In other word, a LC aperture based on such a tandem 90˚-TNLC cell is independent of wavelength and the direction of the polarization of the incident light so that the LC devices have high potential for practical applications. The relationships between the polarization directions of the incident linearly polarized light and the DoLP values of output beams through a single layer 90˚-TNLC and a tandem 90˚-TNLC have been examined experimentally. Moreover, the transmittance spectra in the visible range of the output beam through the analyzer for these two cases of TNLC devices have also been discussed. According to the experimental results, the tandem 90˚-TNLC is more widely applicable than the single 90˚-TNLC due to its properties of independences of wavelength and the direction of input polarization. Finally, the LC aperture can be applied to combine with the properties of light shutters according to the electrical switching. By controlling the conditions of UV illumination and the applied DC voltage, the dose of light can be controlled by such a LC shutter.