本論文研發可以在摻雜染料的液晶薄膜(DDLC)中，利用光配向的機制，來達成液晶預傾角控制的效果。
照射一線性偏振光至一垂直配向的參雜偶氮染料液晶樣品後，偶氮染料甲基紅(Methyl Red, MR)受激發後會吸附在基板上；吸附量會隨著入射光的強度增強或是入射光照射時間變長而增加。當入射光的強度或是入射光照射時間到達某一個強度或是時間的時候，就會產生波紋結構(ripple structure)，根據Berreman理論，波紋結構是提供水平配向力的來源，且波紋結構的深度也和照射強度或是照射時間成正比。固定強度的基板垂直配向力和會隨著照射強度和照射時間變化的水平配向力相互抗衡，由最終的合力來決定液晶的預傾角。最後垂直配向的液晶就會變成一個混合結構(hybrid structure)，中間的液晶層則呈連續變化，從一端的垂直配向到另一端有一預傾角的水平配向。
我們利用量測混合結構的穿透度和電壓曲線圖，再利用1D-Dimos套裝軟體所模擬出來的圖形做比對，來推測液晶的預傾角。
利用這個技術，我們製作了一個pi-cell，量測並分析其反應速度。
除此之外，這一個技術還有很多有潛力的應用，如製作全像光柵或者是可變焦液晶透鏡。

This work demonstrates an approach to control the pre-tilt angle of liquid crystal using photoalignment technique in azo dye-doped liquid crystal (DDLC) films.
By illuminating a homeotropic alignment DDLC sample with a linearly polarized laser beam, the excited dyes (Methyl Red, MR) are adsorbed onto the substrate. The quantity of the adsorbed dyes increases with the pumping beam intensity or illumination duration. The adsorbed dye may form a ripple texture when the illumination duration or intensity is long or strong enough. The amplitude of the ripple structure is proportional to the illumination duration or intensity. Based on the Berreman theory, the ripple structure provides a homogeneous alignment force, and the anchoring force is proportional to the amplitude of the ripple structure. The competition between the constant vertical alignment forces and variable homogeneous force due to the ripple structure determines the final pre-tilt angles of liquid crystals. Finally, a homeotropic alignment DDLC sample becomes a hybrid one, in which the alignment of liquid crystals is homeotropic on one substrate and homogeneous on the other substrate.
We then measure the transmission versus voltage (T-V) curve of the formed hybrid LC cell. By comparing the measured T-V curve with that simulated using 1D-Dimos software, we can determine the pre-tilt angle of liquid crystals.
Using this technique, we fabricate a pi-cell. The response times of the cell are measured and analyzed.
Additionally, several potential applications, such as holographic grating, tunable
liquid crystal lens, can be developed using the present approach.

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