膽固醇液晶光柵具有自組成之特性，除了製作非常容易，最大的優點在於可利用改變外加電場或光場來調控其光柵的繞射角度，因此在光束方向控制(beam-steering)的應用上有很大的潛力。
本論文主要是研究膽固醇液晶光柵的形成方向與其d/P值以及上下基板的配向方向之關係，其中d/P值為液晶盒間距(cell gap, d)與膽固醇液晶螺距(pitch, P)的比值，這裡的P指的是當膽固醇液晶注入液晶元件後因受到上下基板的邊界力影響，為了滿足邊界條件而改變後的螺距，並利用電控和光控來切換膽固醇液晶光柵的方向及改變繞射角度，此外並研究其光學特性。
實驗第一部份探討若上下玻璃基板的配向方向夾一角度φ，且搭配不同的d/Po值時(這裡的Po指的是自然狀態下未改變前之螺距))，膽固醇液晶所形成的膽固醇液晶光柵之方向特性。找出φ與d/Po值對膽固醇液晶光柵形成方向之規則。根據第一部分之結果，第二部分利用控制外加電場來改變膽固醇液晶的螺距之特性，進而改變d/P值，並因此切換膽固醇光柵的形成之方向性。此外並研究不同之d/P光柵可切換性，以及切換方向前後，利用電場調制繞射角度的特性。而第三部分則是利用偶氮染料M5C之光致同素異構化反應，摻雜於膽固醇液晶中，使用紫外光照射使膽固醇液晶螺距變小，照射綠光則可使膽固醇螺距變長，來改變d/P值，製作一可光切換方向之膽固醇液晶光柵。並研究此光柵方向切換前後利用外加電場及照光改變其繞射角度之特性。
綜合上面所述，我們詳細研究了膽固醇液晶光柵形成之方向之原理。並利用電控與光控兩種機制來改變d/P值，成功製作出可切換方向之膽固醇光柵。綜合方向切換以及調控繞射角度，此膽固醇液晶光柵在光柵分向有很大應用之潛力。

A cholesteric liquid crystal (CLC) grating is easily fabricated because of its self-assemble nature. The advantage of a CLC fingerprint grating is that diffraction angle can be tuned by the application of an electrical or optical field. Therefore, CLC fingerprint gratings have high potential for use as beam-steering devices.
This thesis primarily studies the variations of the CLC grating direction with the d/P ratio and the angle φ made by the rubbing directions of top and bottom substrates, where d/P is the film thickness-to-pitch ratio. Applying an electrical or optical field, we can switch the direction of a CLC grating and tune the diffraction angle. Furthermore, we also study the optical properties of the formed CLC gratings.
Experimentally, this thesis consists of three parts. In the first part, we investigate the relationship between the direction of a CLC grating and two parameters, the d/Po ratio (d/Po is the film thickness-to-natural-pitch ratio) and the angle φ made by rubbing directions between top and bottom substrates. The obtained results agree well with the theoretical predictions. In the second part, we use an electrical field to control the pitch and d/P ratio. It allows us to switch the direction of a CLC grating. Furthermore, we investigate the switching property of a CLC grating with a given d/P ratio, and the beam-steering effect under the application of a voltage. In the third part, we use the photo-isomerization effect of the azo dye (M5C) doped in a CLC grating to vary the d/P ratio and achieve the beam-steering effect. The pitch length of a CLC decreases under UV light irradiation. This effect is reversable when the sample is irradiated with green light. Thus, we can use such a photo-isomerization effect to change the d/P ratio to achieve an optically switchable CLC grating. Furthermore, we investigate the beam -steering capability with a CLC grating doped with an azo dye under the applications of both the optical and electrical fields.
Briefly, we have demonstrated that the d/P ratio and pitch of a fingerprint grating can be tuned electrically or optically. Tuning the d/P ratio, and pitch-length, we can switch the grating direction and steer the diffraction angle. Thus, the fabricated CLC grating has a high potential for practical application.

參考文獻(References)
[1] P. Yeh and C. Gu, “Optics of Liquid Crystal Display” , John Wiley & Sons, New York (1999).
[2] E. B. Priestley, P. J. Wojtowicz and P. Sheng, “Introduction to Liquid Crystals” , Princeton, New Jersey (1975).
[3] 松本正一‧角田市良 (劉瑞祥 譯)，「液晶之基礎與應用」，國立編譯館出版，中華民國九十二年。
[4] 顧鴻壽 編著, “光電液晶平面顯示器－第二版”, 新文京開發出版社, (2004).
[5] D. Statman, E. Page, V. Werner and J. C. Lombardi, Phys. Rev. E 75, 021703 (2007).
[6] C.-R. Lee, T.-S. Mo, K.-T. Cheng, T.-L. Fu and Andy Y.-G. Fuh, Appl. Phys. Lett. 83, 4285(2003).
[7] O. Francescangeli, S. Slussarenko and F. Simoni, Phys. Rev. Lett. 82,1855(1999).
[8] F. Reintzer, Monatsh. Chem. 9, 421(1888).
[9] Letter from F. Reintzer to O. Lehmann, reported by H. Keller, Mol. Cryst. Liq. Cryst. 21, 1(1973).
[10] I. C. Khoo, “Liquid Crystals Physical Properties and Nonlinear Optical Phenomena” ,John Wiley & Sons, New York (1995).
[11] R. Hochgesand, H. J. Plach, and I. C. Sage, “Helical Twisting Power of Chiral Dopants in Nematic Liquid Crystals”, Technical report by E. Merck and BDH Chemicals Ltd. (1989).
[12] H.-S. Kitzerrow, C. Bahr, “ Chirality in Liquid Crystals ’’, Springer, New York (2001).
[13] A. Yariv, “Optical Electronics in Modern Communications” ,Oxford University Press, New York, (1997).
[14] A. Yariv, “Quantum Electronics”, Wiley, New York, (1988).
[15] 朱自強, 王仕璠, 蘇顯渝 編著, 現代光學教程, 四川大學出版社, 成都, (1990).
[16] I. C. Khoo and S. T. Wu, “Optics and Nonlinear Optics of Liquid Crystals ”, World Scientific, Singapore, (1993).
[17] M. Marinelli and F. Mercuri, Phys. Rev. E 61, 1616(2000).
[18] Peter J. Collings and Michael Hird, “Introduction to Liquid Crystals Chemistry and Physics”, Taylor & Francis Ltd, Hampshire, (1997).
[19] P. G, De. Gennes and J. Prost, “ The Physics of Liquid Crystal ’’, 2nd ed., Oxford University Press, New York (1993).
[20] P. G. de Gennes, Sol. State Commum. 6, 163 (1968).
[21] R. B. Meyer, Appl. Phys. Lett. 12, 281 (1968).
[22] L. M. Blinov and V. G. Chigrinov, “ Electro-optic Effects in Liquid Crystal Materials ’’, Springer-Verlag, New York (1994).
[23] Shin-Tson Wu and Deng-Ke Yang, “ Reflective Liquid Crystal Displays ’’, John Wiley & Sons Ltd, England (2001).
[24] J. J. Wu, Y. S. Wu, F. C. Chen, and S. H. Chen, Jpn. J. Appl. Phys. 41, L1318–L1320 (2002).
[25] W. M. Gibbons, P. J. Shannon, S. T. Sun and B. J. Swetlin, Nature 351, 49 (1991).
[26] H. K. Lee, A. Kanazawa, T. Shiono and T. Ikeda, Chem. Mater. 10, 5 (1998).
[27] A. G. Chen and D. J. Brady, Opt. Lett. 17, 441 (1992).
[28] T. V. Gastyan, V. Drnoyan and S.M. Arakelian, Phys. Lett. A, 217, 52 (1996).
[29] U. A. Hrozhyk, S. V. Serak, N. V. Tabiryan, and T. J. Bunning, OPTICS EXPRESS, 15, 15(2007).
[30] 王珍珍，『混合聚亞醯胺配向膜調控液晶預傾角之研究及應用』，國立成功大學研究所碩士論文，中華民國九十七年六月.
[31] 陳怡欣，『染料摻雜液晶之雙光效應對像變溫度影響研究及其應用』，國立成功大學研究所碩士論文，中華民國九十六年六月.
[32] D. W. Berreman, Phys. Rev. Lett. 28, 1683(1972).
[33] S. Chandrasekhar, Contemp. Phys. 29, 527 (1988).
[34] Jun Li, Sebastian Gauza, and Shin-Tson Wu, J. Appl. Phys. 96, 19(2004).
[35] 林啟煌，『膽固醇手紋結構液晶薄膜及其應用之研究』，國立成功大學研究所博士論文，中華民國九十一年六月.