Optically Switchable and Tunable Tristable Devices Based on Chiral-Tilted Homeotropic Nematic Liquid Crystals

• Main Authors: Huang, Kuan-Chung, 黃貫中
• Other Authors: Lee, Wei
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/27571918491101848389

碩士 === 國立交通大學 === 光電系統研究所 === 103 === This thesis demonstrates a new photo-induced tristable chiral-tilted homeotropic nematic liquid cyrstals (T-CTHN) based on the trans–cis isomerization of the azo-chiral materials. The antecedent device, biased bistable chiral-tilted homeotropic nematic liquid crystals (B-CTHN), requires the atypical dual-frequency liquid crystal as LC host and a high degree of precision in fabrication including polyimide (PI) mixture concentration, rubbing parameters, cell gap over pitch ratio (d/p) and the pretilt angle. As advancements, the tristable switching mechanism can not only apply to some more readily available nematic materials (e.g. E7) but also reduces the complexity of the fabrication process in all mentioned aspects. Furthermore, this mechanism makes the stable states switch directly as well as widens states from bistable toward tristable, hence broadening the applications of the T-CTHN devices prospectively. Some other variations such as dye-doped T-CTHN as a polarizer-free energy-conservative light modulator or a shutter device, and T-CTHN photonic crystal (T-CTHN–PC)—in which T-CTHN as a defect layer in one-dimentional PC multilayers—as controllable attenuator or wavelength selector have been demonstrated. As the results of spectral characteristics and the prototype photos, the dichromatic-dye-doped T-CTHN can be tuned into multiple gray levels as stable states, and the contrast ratio (CR) was improved to 12:1 with the augmentation of a phase-compensating homogeneous cell. On the other hand, the defect modes in T-CTHN–PC can be as light channels—tunability of transmittance and wavelengths which depend on the incident polarization director or photo-manipulated multiple stable states. Besides, with the fingerprint state (FP) by which the mixed-mode (M-mode) is effectively suppressed, and the defect peak transmittance nearby the central wavelength recedes down to less than 1%, broadens the tunable range by 20% than B-CTHN–PC.