本研究利用膽固醇液晶之手紋結構，並搭配光配向技術製作可廣角調控之環形光柵。膽固醇液晶在適當的d/p值與電壓下，其排列會轉為手紋結構，且該結構具有近似於相位型光柵的週期性條紋。手紋結構根據不同的d/p值，可分為螺距無法調變的Developable-modulation (DM) type (d/p=0.5~1.5) ，以及螺距可調變的Growing-modulation (GM) type (d/p=1.5~3)。本研究藉由控制樣品的d/p值，使其呈現GM type的手紋結構特性，並利用此特性以外加電壓來改變手紋結構之螺距，達到調控繞射角的目的。在本研究中d/p值為2.5的樣品在繞射角調控與光柵成形的表現最佳，其繞射角調控範圍可達22.31度。此外由於環形光柵具有對稱性結構，因此具有無偏振依賴的特性。基於以上優點，此元件不僅對於入射光偏振態的選擇上更為彈性，也可藉由微小電壓即可達到繞射角調控的效果，在光學開關元件上是個相當好的選擇。

This study presents a widely tunable circular gratings base on the photo-alignment method. The fingerprint texture of cholesteric liquid crystals (CLCs) can be obtained under the conditions of the appropriate voltage and d/p ratio. The fingerprint texture with d/p ratio of 0.5~1.5 is defined as the developable-modulation (DM) type, the stripes of fingerprint texture in the DM type will appear simultaneously when applied a low voltage. The fingerprint with d/p ratio of 1.5~3.0 is defined as the growing-modulation (GM) type, the stripes of fingerprint texture in the GM type will extend gradually from defects and along the alignment direction when applied a low voltage. Thus, the pitch of CLCs with GM type can be easily tuned by applying various voltages. Exploiting this characteristic, this work fabricates a tunable circular gratings with CLCs. The results show that the maximum tunable angle of 2nd order diffraction is about 21.51 with d/p ratio 2.5 of the CLC sample. Moreover, the CLC circular gratings have the polarization-independent property because of the circular symmetrical structure. The driven voltage of this gratings is also very small. According to the above advantages, the CLC circular gratings have a great potential in optical applications.

論文審定書 i
致謝 ii
摘要 iii
Abstract iv
目錄 v
圖次 vii
表次 ix
第一章 簡介 1
1-1 前言 1
1-2 液晶簡介 3
(一)液晶的發現 3
(二)何謂液晶 4
(三)液晶的分類 4
1-3 液晶的物理特性 9
(一)秩序參數 9
(二)光學異向性 10
(三)介電異向性 11
(四)彈性連續體形變理論 12
第二章 相關理論 14
2-1 膽固醇液晶的結構變化 14
(一)平面結構 14
(二)手紋結構 14
(三)焦錐結構 14
(四)垂直結構 15
2-2 手紋結構之理論與應用 16
2-3 繞射 18
2-4 光柵 19
2-5 偶氮染料 (azo dye) 20
(一)光致異構化(Photo-isomerization) 20
(二)負力矩效應(Gibbons’ Model) 22
(三)吸附效應 23
第三章 樣品製作與儀器架設 24
3-1 實驗材料 24
(一)向列型液晶 E7 24
(二)旋性分子S811 25
(三)偶氮染料-甲基紅 26
3-2 樣品製作 27
(一)染料摻雜膽固醇液晶的調配 27
(二)玻璃基板清潔 28
(三)液晶盒的製作與封裝 28
3-3 實驗架設 29
(一)圓形光配向的實驗架設 29
(二)觀察手紋結構隨外在電壓的變化 30
(三)圓形光柵的繞射效率量測 31
(四)圓形光柵的繞射角量測 32
(五)圓形光柵的偏振依賴性量測 33
第四章 實驗結果與討論 34
4-1 偏光顯微鏡下觀察手紋結構之條紋變化 34
4-2 以電壓調控繞射角變化 37
4-3 繞射效率 41
4-4 偏振依賴性 44
第五章 研究總結與未來展望 46
5-1 研究總結 46
5-2 未來展望 47
參考文獻 48

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