偶氮染料具有光引致同素異搆化反應，在特定波長的光照射下，會產生順式-反式同素異搆化反應，某些具吸附特性的偶氮染料，經由特定偏振光的照射下，會引致旋轉、擴散、最後吸附在基版表面，吸附之染料能對液晶配向效果，可作為一種光配向技術。此外，偶氮染料之同素異搆化也會改變液晶的相變點或是膽固醇液晶的螺旋結構之螺距，一般認為這是由於順式結構的長棒狀結構傾向穩定液晶態，而反式結構的彎曲狀分子則傾向擾亂液晶態，此種”雜質”效應造成液晶相變點的降低，因此反式結構造成的螺距改變就如同膽固醇液晶溫度升高的效應。在本論文中利用偶氮染料光致同素異搆化對膽固醇液晶螺距的調制，及吸附型染料的光配向機制，製作數種可光控之液晶光電元件。
首先，我們利用摻雜偶氮染料之膽固醇液晶手紋結構，製作出可光控的膽固醇液晶光柵。藉由偶氮染料的光致同素異搆化反應對此膽固醇液晶螺距的改變，調制繞射光的角度。我們研究了在不同波長的光照射下，光控調制及回復的時間，以及在調制後未照光時的穩定時間。利用電場改變此膽固醇液晶光柵繞射角度之特性也被用來和此光控機制比較，並結合電控及光控之機制，達到繞射角度調制最大化。
其次，我們研究了四種不同塑膠基版表面之偶氮染料光配向特性差異。並利用鍍有氧化錫銦 (indium zinc oxide, IZO)透明導電膜的聚碳酸酯 (polycarbonate, PC)基板及雙面光配向機制，製作一可光覆寫記憶型可橈式穿透式液晶顯示元件。此元件可不需外加電場即可維持顯示影像，並可在特定溫度下利用雷射光重新寫入顯示資訊，藉著IZO/PC的良好光配向特性，完整寫入抹除程序可縮短至一分鐘內且具有高對比度。
最後，我們將偶氮染料光配向技術應用在膽固醇液晶光柵的方向轉動上，利用溫度控制雙面光配向技術，進行對膽固醇液晶光柵連續轉向之控制。之後利用軸對稱雙面光配向技術，製作同心圓及放射狀排列之圓形膽固醇液晶光柵，並利用改變外加電場調制此類圓形光柵之繞射圖形。
藉由偶氮染料光致同素異構化對膽固醇液晶螺距的調制效應及光配向技術，這些光控液晶元件都非常容易製作且方便使用。因此他們在光寫入式軟性顯示器及光調制之光導向元件領域都有很大的應用潛力。

The photo-alignment technique used in this study is based on the photo-induced adsorption effect of azo dye doped in a liquid crystal (LC) host. When an azo dye-doped LC (DDLC) cell is excited by a suitable light, azo dye molecules in the LC host undergo trans-cis isomerization, producing reorientation, diffusion, and finally, adsorption onto the substrate surface(s). The adsorbed dye then reorients LC molecules inducing the photo-alignment. The isomerization effect can also be used to photo-switch the liquid crystal phase of a material from cholesteric to nematic or to change the pitch length of a cholesteric phase. The reason is generally considered as follows. The trans-isomers are favorable for stabilization of the cholesteric phase due to its rod-like shape. On the other hand, the bent cis-isomers tend to destabilize the phase structure, resulting in lowering of TN-I as in the case of depression of a melting point since it acts as an “impurity” in the system. Thus, the change in pitch induced by the cis-isomers is similar to increase to temperature of the cholesteric liquid crystal (CLC). In this thesis, we demonstrate several optically controlled liquid crystal devices by adapting the CLCs’ pitch shift effect with photo-isomerization and the photo-alignment effect of the of azo dyes.
Firstly, we demonstrate an optically switchable beam steering device that is based on an azobenzene-doped CLC fingerprint texture. The photoisomerization of azobenzene varies the pitch length of CLC and shifts the diffraction angle of the fingerprint texture. We study the tuning time and the reversing time with and without the illumination by light of different wavelengths. The electrical tuning effect is also demonstrated and compared with the optical effect. Combining the optical and electrical effects, we can maximize the tuning range.
Secondly, we study various photo-alignment characteristics of four different substrate surfaces of the plastic substrates, and develop a photo-rewritable transmissive flexible-LCD based on the alignment effect of the photo-induced adsorption of azo dye on flexible indium zinc oxide/polycarbonate (IZO/PC) substrates and adapting the double-sided photo-alignment method. Images can be displayed without applying an external field and rewritten by changing the direction of the writing laser beam while the cell temperature is controlled. By using IZO/PC substrates, the writing and erasing processes can be achieved within 1 min with a high contrast.
Finally, we study the rotation of the CLC grating direction by adapting the photo-alignment of the azo-dye. We demonstrate the optical direction-tuning of cholesteric liquid crystal grating by using the temperature controlled double-sided photo-alignment. Then we propose a radial and an azimuthal circular CLC grating by using the axially symmetrical double-sided photo-alignment, and tuning the diffraction pattern by varying electrical field.
Adapting the photo-alignment effect and the pitch shift of the CLCs with the photo-isomerization of azo dyes allows us to fabricate these optically controlled liquid crystal devices. The fabrications are simple, and the devices are very convenient to use. Thus, they have highly potential for practical applications in optically rewritable flexible display and optical controlled beam steering devices.

References
1. F. Reinitzer, "Beiträge zur Kenntniss des Cholesterins," Monatshefte für Chemie / Chemical Monthly 9, 421-441 (1888).
2. P. G. d. Gennes and J. Prost, The physics of liquid crystals, 2nd ed., Oxford science publications (Clarendon Press ;Oxford University Press, Oxford;New York, 1993).
3. E. B. Priestley, P. J. Wojtowicz, and P. Sheng, Introduction to liquid crystals (Plenum Press, New York, 1975), pp. xi, 356 p.
4. S. Chandrasekhar, Liquid Crystals (Cambridge University Press, 1992).
5. I.-C. Khoo and S.-T. Wu, Optics and nonlinear optics of liquid crystals, Series in nonlinear optics (World Scientific, Singapore ; River Edge, NJ, 1993), pp. xii, 425 p.
6. D. Demus, J. Goodby, G. W. Gray, H. W. Spiess, and V. Vill, Handbook of Liquid Crystals (Wiley-VCH Verlag GmbH, 2008), pp. 897-914.
7. C. W. Ossen, "The theory of liquid crystals," Trans. Faraday Soc. 29, 833-899 (1933).
8. H. Zocher, "The effect of a magnetic field on the nematic state," Trans. Faraday Soc. 29, 945-957 (1933).
9. F. C. Frank, "On the Theory of Liquid Crystals," Discuss. Faraday Soc 25(1958).
10. A. D. McNaught, A. Wilkinson, and International Union of Pure and Applied Chemistry., Compendium of chemical terminology : IUPAC recommendations, 2nd ed. (Blackwell Science, Oxford [Oxfordshire] ; Malden, MA, 1997), pp. vii, 450 p.
11. D. Voloshchenko, A. Khyzhnyak, Y. Reznikov, and V. Reshetnyak, "Control of an Easy-Axis on Nematic-Polymer Interface by Light Action to Nematic Bulk," Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers 34, 566-571 (1995).
12. F. Simoni and O. Francescangeli, "Effects of light on molecular orientation of liquid crystals," Journal of Physics-Condensed Matter 11, R439-R487 (1999).
13. E. Ouskova, Y. Reznikov, S. V. Shiyanovskii, L. Su, J. L. West, O. V. Kuksenok, O. Francescangeli, and F. Simoni, "Photo-orientation of liquid crystals due to light-induced desorption and adsorption of dye molecules on an aligning surface," Physical Review E 64, 051709 (2001).
14. D. Fedorenko, E. Ouskova, V. Reshetnyak, and Y. Reznikov, "Evolution of light-induced anchoring in dye-doped nematics: Experiment and model," Physical Review E 73, 031701 (2006).
15. A. Y. G. Fuh, C. C. Liao, K. C. Hsu, C. L. Lu, and C. Y. Tsai, "Dynamic studies of holographic gratings in dye-doped liquid-crystal films," Optics Letters 26, 1767-1769 (2001).
16. C. R. Lee, T. L. Fu, K. T. Cheng, T. S. Mo, and A. Y. G. Fuh, "Surface-assisted photoalignment in dye-doped liquid-crystal films," Physical Review E 69, - (2004).
17. K.-T. Cheng, "Studies of Biphotonic Effect in Azo-Dye-Doped Liquid Crystal films and Their Applications," (National Cheng Kung University 2006).
18. I. Janossy and T. Kosa, "Influence of Anthraquinone Dyes on Optical Reorientation of Nematic Liquid-Crystals," Optics Letters 17, 1183-1185 (1992).
19. T. Kosa and I. Janossy, "Anomalous Wavelength Dependence of the Dye-Induced Optical Reorientation in Nematic Liquid-Crystals," Optics Letters 20, 1230-1232 (1995).
20. I. Jánossy, A. Vajda, T. Paksi, and T. Kósa, "Photoinduced Surface Alignment: The Role of Liquid-Crystalline Order," Molecular Crystals and Liquid Crystals 359, 157 - 166 (2001).
21. I. Janossy, A. D. Lloyd, and B. S. Wherrett, "Anomalous Optical Freedericksz Transition in an Absorbing Liquid-Crystal," Molecular Crystals and Liquid Crystals 179, 1-12 (1990).
22. I. Janossy, "Molecular Interpretation of the Absorption-Induced Optical Reorientation of Nematic Liquid-Crystals," Physical Review E 49, 2957-2963 (1994).
23. W. M. Gibbons, P. J. Shannon, S. T. Sun, and B. J. Swetlin, "Surface-Mediated Alignment of Nematic Liquid-Crystals with Polarized Laser-Light," Nature 351, 49-50 (1991).
24. F. Simoni and O. Francescangeli, "Effects of light on molecular orientation of liquid crystals," Journal of Physics: Condensed Matter 11, R439 (1999).
25. L. C. Lin, H. C. Jau, T. H. Lin, and A. Y. G. Fuh, "Highly efficient and polarization-independent Fresnel lens based on dye-doped liquid crystal," Optics Express 15, 2900-2906 (2007).
26. T.-H. Lin, "Study of Spatial Filters based on Liquid Crystal Devices and their Applications," (National Cheng Kung University 2006).
27. S.-T. Wu and D.-K. Yang, Reflective liquid crystal displays, Wiley SID series in display technology (Wiley, Chichester Eng. ; New York, 2001), pp. xvi, 335 p.
28. L. M. Blinov and V. G. Chigrinov, Electrooptic effects in liquid crystal materials, Partially ordered systems (Springer-Verlag, New York, 1994), pp. xvii, 464 p.
29. C. H. Lin, "Studies of Cholesteric Fingerprint Texture Films and Their Applications," (National Cheng Kung University 2002).
30. R. B. Meyer, "Effects of Electric and Magnetic Fields on Structure of Cholesteric Liquid Crystals," Applied Physics Letters 12, 281-& (1968).
31. H. K. Lee, K. Doi, H. Harada, O. Tsutsumi, A. Kanazawa, T. Shiono, and T. Ikeda, "Photochemical modulation of color and transmittance in chiral nematic liquid crystal containing an azobenzene as a photosensitive chromophore," Journal of Physical Chemistry B 104, 7023-7028 (2000).
32. H. K. Lee, A. Kanazawa, T. Shiono, T. Ikeda, T. Fujisawa, M. Aizawa, and B. Lee, "All-optically controllable polymer liquid crystal composite films containing the azobenzene liquid crystal," Chemistry of Materials 10, 1402-1407 (1998).
33. J. J. Wu, Y. S. Wu, F. C. Chen, and S. H. Chen, "Formation of phase grating in planar aligned cholesteric liquid crystal film," Japanese Journal of Applied Physics Part 2-Letters 41, L1318-L1320 (2002).
34. J. H. Liu and H. Y. Wang, "Optical switching behavior of polymer-dispersed liquid crystal composite films with various novel azobenzene derivatives," Journal of Applied Polymer Science 91, 789-799 (2004).
35. S.-Y. Huang, Y.-S. Chen, H.-C. Jau, M.-S. Li, J.-H. Liu, P.-C. Yang, and A. Y.-G. Fuh, "Biphotonic effect-induced phase transition in dye-doped cholesteric liquid crystals and their applications," Optics Communications 283, 1726-1731 (2010).
36. K. Hirabayashi, T. Yamamoto, and M. Yamaguchi, "Free-Space Optical Interconnections with Liquid-Crystal Microprism Arrays," Applied Optics 34, 2571-2580 (1995).
37. K. Hirabayashi and T. Kurokawa, "Liquid-Crystal Devices for Optical Communication and Information-Processing Systems," Liquid Crystals 14, 307-317 (1993).
38. D. Faklis and G. M. Morris, "Diffractive optics technology for display applications," in (SPIE, 1995), 57-61.
39. J. J. P. Drolet, E. Chuang, G. Barbastathis, and D. Psaltis, "Compact, integrated dynamic holographic memory with refreshed holograms," Optics Letters 22, 552-554 (1997).
40. D. Subacius, S. V. Shiyanovskii, P. Bos, and O. D. Lavrentovich, "Cholesteric gratings with field-controlled period," Applied Physics Letters 71, 3323-3325 (1997).
41. C. M. Titus, P. J. Bos, and O. D. Lavrentovich, "Efficient accurate liquid crystal digital light deflector," in (SPIE, 1999), 244-253.
42. X. Wang, D. Wilson, R. Muller, P. Maker, and D. Psaltis, "Liquid-crystal blazed-grating beam deflector," Applied Optics 39, 6545-6555 (2000).
43. A. Y. G. Fuh, C. H. Lin, M. F. Hsieh, and C. Y. Huang, "Cholesteric gratings doped with a dichroic dye," Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers 40, 1334-1338 (2001).
44. N. V. Tabiryan and S. R. Nersisyan, "Large-angle beam steering using all-optical liquid crystal spatial light modulators," Applied Physics Letters 84, 5145-5147 (2004).
45. L. Shi, P. F. McManamon, and P. J. Bos, "Liquid crystal optical phase plate with a variable in-plane gradient," Journal of Applied Physics 104, - (2008).
46. J. B. Yang, X. Y. Su, P. Xu, and Z. Gu, "Beam steering and deflecting device using step-based micro-blazed grating," Optics Communications 281, 3969-3976 (2008).
47. N. Bennis, M. A. Geday, X. Quintana, B. Cerrolaza, D. P. Medialdea, A. Spadlo, R. Dabrowski, and J. M. Oton, "Nearly-analogue blazed phase grating using high birefringence liquid crystal," Opto-Electronics Review 17, 112-115 (2009).
48. E. Sackmann, S. Meiboom, L. C. Snyder, A. E. Meixner, and R. E. Dietz, "On Structure of Liquid Crystalline State of Cholesterol Derivatives," Journal of the American Chemical Society 90, 3567-& (1968).
49. M. Kawachi, K. Kato, and O. Kogure, "Light-Scattering Characteristics in Nematic-Cholesteric Mixtures with Positive Dielectric Anisotropy," Japanese Journal of Applied Physics 17, 1245-1250 (1978).
50. V. Vinogradov, A. Khizhnyak, L. Kutulya, Y. Reznikov, and V. Reshetnyak, "Photoinduced Change of Cholesteric Lc-Pitch," Molecular Crystals and Liquid Crystals 192, 273-278 (1990).
51. T. J. White, R. L. Bricker, L. V. Natarajan, N. V. Tabiryan, L. Green, Q. Li, and T. J. Bunning, "Phototunable Azobenzene Cholesteric Liquid Crystals with 2000 nm Range," Advanced Functional Materials 19, 3484-3488 (2009).
52. S. W. Kang, S. Sprunt, and L. C. Chien, "Structure and morphology of polymer-stabilized cholesteric diffraction gratings," Applied Physics Letters 76, 3516-3518 (2000).
53. S. W. Kang, S. Sprunt, and L. C. Chien, "Polymer-stabilized cholesteric diffraction gratings: Effects of UV wavelength on polymer morphology and electrooptic properties," Chemistry of Materials 18, 4436-4441 (2006).
54. L. De Sio, S. Serak, N. Tabiryan, S. Ferjani, A. Veltri, and C. Umeton, "Composite Holographic Gratings Containing Light-Responsive Liquid Crystals for Visible Bichromatic Switching," Advanced Materials 22, 2316-2319 (2010).
55. G. P. Crawford, Flexible flat panel displays, Wiley SID series in display technology (John Wiley & Sons, Chichester, West Sussex, England ; Hoboken, NJ, 2005), pp. xxviii, 528 p.
56. H. Haruo, K. Hideo, G. Makoto, O. Yasunoti, and A. Hiroshi, "A New Color Imaging Method for Photo-Addressable Electronic Paper," Proc Int Disp Workshops 11, 1703-1706 (2004).
57. N. Hiji, T. Kakinuma, M. Araki, T. Hikichi, H. Kobayashi, and S. Yamamoto, "50.2: Cholesteric Liquid Crystal Micro-Capsules with a Perpendicular Alignment Shell for Photo-Addressable Electronic Paper," SID Symposium Digest of Technical Papers 36, 1560-1563 (2005).
58. R. C. Liang, J. Hou, H. Zang, J. Chung, and S. Tseng, "Microcup[registered sign] displays: Electronic paper by roll-to-roll manufacturing processes," Journal of the Society for Information Display 11, 621-628 (2003).
59. D. K. Yang, J. L. West, L. C. Chien, and J. W. Doane, "Control of Reflectivity and Bistability in Displays Using Cholesteric Liquid-Crystals," Journal of Applied Physics 76, 1331-1333 (1994).
60. T. H. Lin, H. C. Jau, S. Y. Hung, H. R. Fuh, and A. Y. G. Fuh, "Photoaddressable bistable reflective liquid crystal display," Applied Physics Letters 89, - (2006).
61. A. Muravsky, A. Murauski, X. H. Li, V. Chigrinov, and H. S. Kwok, "Optical rewritable liquid-crystal-alignment technology," Journal of the Society for Information Display 15, 267-273 (2007).
62. T. H. Lin, Y. H. Huang, A. Y. G. Fuh, and S. T. Wu, "Polarization controllable Fresnel lens using dye-doped liquid crystals," Optics Express 14, 2359-2364 (2006).
63. S. W. Ko, Y. Y. Tzeng, C. L. Ting, A. Y. G. Fuh, and T. H. Lin, "Axially symmetric liquid crystal devices based on double-side photo-alignment," Optics Express 16, 19643-19648 (2008).
64. H. Hara, T. Shiro, and T. Yatabe, "Optimization and properties of Zn doped indium oxide films on plastic substrate," Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers 43, 745-749 (2004).
65. Y. G. Cao, L. Miao, S. Tanemura, M. Tanemura, Y. Kuno, Y. Hayashi, and Y. Mori, "Optical properties of indium-doped ZnO films," Japanese Journal of Applied Physics Part 1-Regular Papers Brief Communications & Review Papers 45, 1623-1628 (2006).
66. H. J. Kim, J. G. Lee, H. G. Kim, S. W. Choi, and S. S. Kim, "Liquid Crystal Device with Nanopatterned Indium-Zinc-Oxide Layer," Japanese Journal of Applied Physics 49, - (2010).
67. S. Y. Huang, S. T. Wu, and A. Y. G. Fuh, "Optically switchable twist nematic grating based on a dye-doped liquid crystal film," Applied Physics Letters 88, - (2006).
68. T. Nose, T. Miyanishi, Y. Aizawa, R. Ito, and M. Honma, "Rotational Behavior of Stripe Domains Appearing in Hybrid Aligned Chiral Nematic Liquid Crystal Cells," Japanese Journal of Applied Physics 49, - (2010).