現今科技發展快速，液晶光電應用於顯示器技術已相當成熟，同時國內外研發團隊也積極致力於其他相關領域之應用與開發。此外，偏振光學的特性在許多光電產品的應用上也扮演著相當重要的角色，如上述提及之液晶顯示器及3D立體眼鏡等，皆為涵蓋偏振光學的應用，因此調控光的偏振性必然成為光電領域中極為重要的一環。然而，目前市面上改變線性偏振光之光學元件，如半波板(Half-wave plate)、扭轉向列型液晶 (Twisted nematic liquid crystal，簡稱TN-LC)結構等元件，皆有不同的優缺點，如半波板僅針對單一波長有最好的線偏振轉換效應，且必須旋轉光軸方能改變線偏振旋轉之角度，而TN-LC則須符合Mauguin limit方能具備偏振旋轉特性，且無法任意改變線偏振旋轉角度等缺點。換言之，若能開發出不同的方法製造更新穎的光學元件，用以改變線性偏振光之偏振角度，且能彌補上述既有元件的缺點，相信其應用潛力將極為廣大。
本論文提出利用照射紫外光於摻雜偶氮苯手性分子之膽固醇液晶，以改變膽固醇液晶螺距長度，進而達到旋轉線性偏振光偏振角度之液晶元件。根據實驗結果，若製成一具平面結構之膽固醇液晶，且其布拉格反射波長調配於紅外光波段，或更長波長區域時，當入射於該液晶元件的電磁波，其波長為相較於該膽固醇液晶之布拉格反射波段較短的區域，如可見光或近紅外光，其電場振盪(偏振)方向會受液晶層的影響而改變，亦即可旋轉線性偏振之角度，且該旋轉角度與波長、螺距長度及螺距數量等有關。本論文將分別討論(1)線性偏振旋轉角度與上述因素之關係、 (2)摻雜偶氮苯材料製作可光控之線性偏振旋轉器及(3)實驗與軟體模擬之驗證。

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.

參考文獻
[1] B. Bahoadur, Liquid crystals-applications and uses, (World Scientific Press, 1990).
[2] F. Reinizer, “Beitrage zur kenntiniss des cholesterins,” Monatsh. Chem. 9, 421 (1888).
[3] O. Lehmam, “On flowing crystals,” Z. Phys. Chem. 4, 462 (1889).
[4] 陳言愈，電控及光控膽固醇液晶光柵之研究 (國立成功大學，碩士論文，民國100年).
[5] E. G. Virga, Variational theories for liquid crystals, (Chapman & Hall London, 1994).
[6] I. C. Khoo and S. T. Wu, Optics and nonlinear optics of liquid crystals, (World Scientific, 1993).
[7] O. Francescangeli, S. Slussarenko, and F. Simoni, “Light-induced surface sliding of the nematic director in liquid crystals,” Phys. Rev. Lett. 82, 1855 (1999).
[8] M. Marinelli and F. Mercuri, “Effects of fluctuations in the orientational order parameter in the cyanobiphenyl (nCB) homologous series,” Phys. Rev. E 61, 1616 (2000).
[9] 松本正一，角田市良，液晶之基礎與運用 (國立編譯館, 1996).
[10] H. Keller, “History of liquid crystals,” Mol. Cryst. Liq. Cryst. 21, 1 (1973).
[11] G. W. Gray, Thermotropic liquid crystals, (the Society of Chemical Industry 1987).
[12] W. H. de Jeu, Physical properties of liquid crystalline materials, (Gordon & Breach, 1980).
[13] H. S. Kitzerrow and C. Bahr, Chirality in Liquid Crystals, (Springer, New York, 2001).
[14] P. J. Collings and Michael Hird, Introduction to liquid crystals chemistry and physics, (Taylor ＆ Francis Ltd, 1997).
[15] A. Yariv, Optical Electronics in Modern Communications, (Oxford University Press, New York, 1997).
[16] A. Yariv, Quantum Electronics, (Wiley, New York, 1988).
[17] P. Yeh and C. Gu, Optics of liquid crystal displays, (John Wiley ＆ Sons, Inc., 2006).
[18] G. R. Fowles, Introduction to modern optics, 2nd ed., (University of Utah, 1975).
[19] M. Hara, H. Takezoe, and A. Fukuda, “Forced Rayleigh scattering in nCB's (n=5-9) with methyl red and binary mass diffusion constants,” Jpn. J. Appl. Phys. 25, 1756 (1986).
[20] P. G. de Gennes, and J. Prost, The physics of liquid crystals, (Oxford University Press, 1993).
[21] L. M. Blinov and V. G. Chigrinov, Electrooptic effects in liquid crystal materials, (Springer-Verlag Publishing Co., 1994).
[22] V. Fréedericksz and A. Repiewa, “Theoretisches und experimentelles zur frage nach der natur der anisotropen flüssigkeiten,” Zeitschrift fur Physik 42, 532 (1927).
[23] S. T. Wu and D. K. Yang, Reflective liquid crystal displays, (John Wiley ＆ Sons Ltd, 2001).
[24] P. G. de Gennes, “CALCUL DE LA DISTORSION D’UNE STRUCTURE CHOLESTERIQUE PAR UN CHAMP MAGNETIQUE,” Sol. State Commun. 6, 163 (1968).
[25] R. B. Meyer, “Effects of electric and magnetic fields on the structure of cholesteric liquid crystals,” Appl. Phys. Lett. 12, 281 (1968).
[26] T. V. Galstyan, V. E. Drnoyan, and S. M. Arakelian, “Self-induced oscillations and asymmetry of the light angular spectrum in a dye doped nematic,” Phys. Lett. A 217, 52 (1996).
[27] Y. C. Liu, K. T. Cheng, H. F. Chen and A. Y. G. Fuh, “Photo- and electro-isomerization of azobenzenes based on polymer-dispersed liquid crystals doped with azobenzenes and their applications,” Opt. Express 22, 4404 (2014).
[28] Eugene Hecht, Optics (4th edition), (Addison Wesley, 2001).
[29] A. Yariv and P. Yeh, Optical waves in crystals: propagation and control of laser radiation, (John Wiley & Sons Inc, 2002).
[30] 丁啟倫，運用二維時域有限差分法分析液晶元件光學性質 (國立成功大學，碩士論文，民國94年).
[31] 林宗賢，液晶光子晶體雷射現象與其光控制研究 (國立成功大學，碩士論文，民國92年).
[32] K. T. Cheng, P. Y. Lee, M. M. Qasim, C. K. Liu, W. F. Cheng, and T. D. Wilkinson, “Electrically switchable and permanently stable light scattering modes by dynamic fingerprint chiral textures,” ACS Appl. Mater. Interfaces 8, 10483 (2016).
[33] Q. Li, L. Green, N. Venkataraman, I. Shiyanovskaya, A. Khan, A. Urbas, and J. W. Doane, “Reversible photoswitchable axially chiral dopants with high helical twisting power,” J. Am. Chem. Soc. 129, 43 (2007).
[34] 許維婷，液晶盒厚度量測方法的研究 (國立成功大學，碩士論文，民國93年).
[35] S. W. Ko, S. H. Huang, A. Y. G. Fuh, and T. H. Lin, “Measurement of helical twisting power based on axially symmetrical photo-aligned dye-doped liquid crystal film,” Opt. Express 17, 15927(2009).