| dc.description.abstract | Nowadays, development of technology is rapidly getting better and better. The applications of liquid crystals on display technology are considerably matured. At the same time, many scientists have also been paying much attention to the relative applications. Additionally, the characteristics of polarization optics, used in many electro-optical products, such as liquid crystal displays, 3D technology, etc., therefore, play the very important roles. Hence, it is the modulation of light polarization that has become a significant technique in electro-optical field. Regarding the rotation of polarization direction of linearly polarized light, the currently developed electro-optical products, such as half-wave plates, twisted nematic liquid crystal (TN-LC), and others, for modulating the polarization direction of linearly polarized light possess their different pros and cons. It can be understood that the performance of a half-wave plate is wavelength dependent, and its optical axis should be mechanically rotated to change the polarization direction of the incident linearly polarized light. Moreover, TN-LC can be able to rotate the polarization direction of the incident linearly polarized light to a specific angle within the Mauguin limit so that it cannot be used to simply change the polarization direction of the incident linearly polarized light. Hence, the development of novel optical devices to rotate the polarization direction of the incident linearly polarized light is a significantly important trend.
This study presents a novel approach to rotate the polarization direction of linearly polarized light from one angle to others via the exposure of UV light based on chiral azobenzene-doped cholesteric liquid crystals (CLCs). Because the adopted chiral azobenzene is a kind of chiral dopants with optically tunable helical twisting power, the polarization direction of linearly polarized light can be rotated optically due to the optical tuning of the CLCs pitch length. According to the experimental results, if the CLCs with planar textures and with the selective Bragg reflection of wavelength longer than infrared, the polarization direction of the incident linearly polarized light with relative shorter wavelength (visible wavelength and near infrared) can be rotated. Notably, the rotated angle is dependent on the wavelength of incident light, the pitch length of CLCs, the pitch numbers, and others. In this thesis, the following three topics will be reported and discussed, including (1) various factors described above to affect the rotation of the polarization direction of linearly polarized light; (2) demonstration of an optically controllable linear-polarization rotator using chiral azobenzene-doped CLCs and (3) verification and comparison of experimental and simulated results. | en_US |