光子晶體是一種具有高度折射率週期性結構分布及具有光子能隙的介電物質。波長介於能隙之間的光子將無法在光子晶體之中傳遞。光子晶體的能隙對於由雷射染料被激發產生的螢光光譜具有相當程度上的影響力；也就是說，螢光在能隙中會被抑制而在能隙的邊緣能夠被有效放大。位於能隙邊緣的螢光經由多重反射的形式傳遞這導致了這樣的螢光具有群速度非常小以及光子狀態密度非常地大的特性。這是由於在光子晶體內多重反射的過程中所造成的主動多層結構之分布反饋式增益，位在能隙邊緣處自發及受激輻射的比例將同時被放大，因此可得到一高增益性且低臨界值的雷射輸出。所以，這類的光子晶體能夠被應用在不需反射鏡的雷射共振腔之中。膽固醇液晶具有長程上一維折射率分布的特性，主要是由棒狀液晶分子沿螺旋軸連續地排列及扭轉所形成，如此的結構有如一維類光子晶體結構。因此，平面型的染料摻雜膽固醇液晶將能被視為具有低臨界值的一維分布反饋式邊緣型雷射。
本論文中，我們研究及製作出在外加一直流電壓下同時具有光控及電控雷射輸出波長能力之鍍有光導電膜的平面型的染料摻雜膽固醇液晶樣品。雷射波長的調控能力主要是歸因於對流不穩定性所造成的光及電的可控制性，如此導致了能有效地改變膽固醇液晶螺旋軸的方向。對流不穩定效應的產生主要是由於外加一直流電場以及液晶的導電率異向性所導致。藉由改變連續波綠光雷射照射強度或外加直流電壓的大小，光電引致表面電荷的屏蔽效應能夠透過對流不穩定效應的程度來加以控制，如此將導致染料摻雜膽固醇液晶雷射輸出波長的變化。

Photonic crystals (PCs) are dielectric materials with sufficiently high periodic modulation of the refractive index having structure with photonic bandgaps. The photons with wavelengths within such bandgaps are stopped from propagating inside PCs. The bandgaps in PCs can significantly change the fluorescence spectrum generated by excitation of doped active dyes; that is, fluorescence can be suppressed inside gaps and enhanced at band edges.
Fluorescence can propagate via multi-reflection at band edges, resulting in a very slow group velocity and very large density of photonic state (DOS) for fluorescence. Due to the distributed feedback of the active multilayer of the PC in the multi-reflection process, the rates of spontaneous and stimulated emissions at band edges are both enhanced, such that a high gain can be attained for a low-threshold lasing emission. Such PCs, consequently, can be used as mirrorless lasing resonators. Cholesteric liquid crystal (CLC) has a large one-dimensional (1D) modulation of the refractive index, in which rod-like LC molecules assemble and rotate continuously along the helical axis, forming a 1D PC-like planar structure. Thus, the planar dye-doped CLC (DDCLC) can be considered as a 1D distributed-feedback laser with low-threshold edge lasing emissions.
In this thesis, we fabricate and investigate an optically and electrically tunable laser in a single planar DDCLC cell with a photoconductive polymer layer in the presentation of an applied dc voltage. The tunability of the lasing wavelength is attributable to the optical or
electrical controllability of the convective instability, resulting in the effective variation of the helical direction of the CLC. The convective instability effect
is formed by the presentation of the applied dc field and the anisotropic conductivity of LCs. By changing the intensity of the irradiated CW green beam or the magnitude of the applied dc voltage, the photoelectro-induced
screen effect of the surface charges can be controlled to vary the intensity of the convective instability effect, which in turn causes the variation of the wavelength of the lasing emission in the DDCLC.

[1] P. G. de Gennes and J. Prost, “The Physics of Liquid Crystals”, 2nded., Clarendon Press, Oxford (1993).

[2] L. M. Blinov and V. G. Chigrinov, “Electrooptic Effects in Liquid Crystal Materials”, Springer-Verlag Publishing Co., New York (1994).

[3] B. Bahadur, “Liquid Crystals：Applications and Uses”, Vol. 1, World Scientific, Singapore (1990).

[4] G. W. Gray, “Thermotropic Liquid Crystals”, the Society of Chemical Industry (1987).

[5] Birendra Bahadur, “Liquid Crystals：Applications and Uses”, Vol. 3, World Scientific, Singapore (1990).

[6] H.-S. Kitzerow, C. Bahr,”Chirality in Liquid Crystals”, Springer, New York (2001).

[7] Andrew J. Lovinger, Karl R. Amundson and Don D. Davis, Chem. Mater. 6, 1726 (1994).

[8] Grant R. Fowles,“Introduction to Modern Optics”, 2nd
ed., University of Utah, New York (1975).

[9]朱自強、王仕璠與蘇顯渝,『現代光學教程』 ，四川大學出版社，成都(1990).

[10] A. Yariv, “Quantum Electronics”, John Wiley & Sons Press, New York (1989).

[11] Iam-Choon Khoo, “Liquid Crystals-Physical Properties and Nonlinear

Optical Phenomena”, John Wiley & Sons Press, New York (1995).

[12] C. W. Oseen, Trans. Faraday Soc. 29, 883 (1933).

[13] H. Zocher, Trans. Faraday Soc. 29, 19 (1933).

[14] F. C. Frank, Discuss. Faraday Soc. 25, 19 (1958).

[15] 1.P. G. de Gennes and J. Prost,“The Physics of Liquid Crystals,” 2nded.,
Clarendon Press, Oxford (1993).

[16] H. Kozawaguchi and M. Wada, Mol. Crys. Liq. Crys. 45, 55 (1978).

[17] P. G. de Gennes, Sol. State Commun. 6, 163 (1968).

[18] L. M. Blinov and V. G. Chigrinov, “Electrooptic Effects in Liquid Crystal Materials,” Springer-Verlag, New York (1994).

[19] R. B. Meyer, Appl. Phys. Lett. 12, 281 (1968).

[20] W. Helfrich, Phys. Rev. Lett. 23, 372 (1969).

[21] Jonathan P. Dowling, J. Appl. Phys. 75, 1896(1994).

[22] V. I. Koop, Opt. Lett. 23, 1707(1998).

[23] Amon Yariv and Pochi Yeh,“Optical Waves in Crystals”, John Wiley & Sons Press, New York(1984).

[24] Jonathan P. Dowling, J. Appl. Phys. 75, 1896 (1994).

[25] V. I. Koop, Opt. Lett. 23, 1707 (1998).

[26] A. Munoz F, Opt. Lett. 26, 804 (2001).

[27] L. S. Goldberg and J. M. Schnur, U.S. patent 3, 771, 065 (1973).

[28] Heino Finkelmann, Adv. Matter. 14, 1069 (2001).

[29] Henk Bolink, “Photorefractive Polymers”, University of Groningen,Netherlands. (1997).

[30] H. Hoegl, J. Phys. Chem. 69, 755 (1965).

[31] M. Lardon, E. Lell-Doller, and J. C. Weigl, Mol. Cryst. 2, 241 (1967).

[32] P. J. Regensburger, Photochem. and Photobial. 8, 249 (1968).

[33] Wang Y , Nature 356, 585 (1992).

[34] A. Dyadyusha, M. Kaczmarek, and S. Slussarenko, “electronic-Liquid Crystal Communications,” December 23, (2003).

[35] Q. D. Ling, S. L. Lim, Y. Song, C. X. Zhu, D. S. H. Chan, E. T. Kang,K. G. Neoh, Langmuir, 23, 312 (2007).

[36] K. YOSHINO, S. MO'RITA, X. H. YIN, S. SHAKUDA and T.KAWAI, Conduction and Breakdown in Dielectric Liquids,1993,ICDL '93, IEEE 11th International Conference

[37] A. Watanabe and O. Ito, J. Chem. Soc., Chem. Commun. 1285, (1994).

[38] C. Wang, W. Ming and S. Fu, Polymer Bulletin 35, 177 (1995).

[39] W. England and M. J. S. Dewar, “Molecular Orbitals”, Springer-Verlag, (1971).
[40] A. F. Hebard et al., Nature 350, 600 (1991).

[41] M. A. Greaney and S. M. Gorun, J. Phys. Chem., 95, 7142 (1991).

[42] A. G. Jepsen, D. Wright, B. Smith, M. S. Bratcher, M. S. DeClue, J. S. Siegel, and W. E. Moerner, Chem. Phys. Lett. 291, 553 (1998).

[43] H. Mada and K. Osajima, J. Appl. Phys. 60, 3111 (1986)

[44] A. Sugimura, N. Matsui, Y. Takahashi,H. Sonomura, H. Naito, and M.Okuda, Phys. Rev. B, 43, 8272 (1991).

[45] A. Mochizuki, T. Yoshihara, K. Motoyoshi, and S. Kobayashi, J. Jpn. Appl. Phys. 29, 322 (1990).

[46] F. L. Vladimirov, A. N. Chaika, I. E. Morichev, N. I. Pletneva, A. F. Naumov, and M. Yu. Loktev, J. Opt. Technol. 67, 712 (2000).

[47] H. T. Li and Paul J. Regensburger, J. Appl. Phys. 34, 1730 (1963).

[48] R. Williams, J, Chem. Phys. 39, 384 (1963).

[49] W. Helfrich, J. Chem. Phys. 51, 4092 (1969).

[50] D.Demus, J.Goodby, G.W.Gray, H.-W.Spiess,V.Vill, ”Handbook of Liquid Crystals,” Chap.9,Wiley-VCH, New York (1998).