偏振分光鏡的主要功用是分開兩種線偏振態(s波與p波)的傳播方向，對於液晶顯示、光通訊、光儲存及其他光學系統來說是很重要的元件。本研究使用兩個高折射率稜鏡(n = 1.778)及一光敏感液晶夾層(ne = 1.7126; no = 1.5287)來製作可切換分光功能的偏振分光鏡。此偏振分光鏡的工作機制為：當光由密介質(稜鏡)傳播到疏介質(液晶)時，若入射角大於特定角度即產生全反射。藉由液晶雙折射的特性，使得s波與p波分別在液晶層感受到不同的折射率而造成不同的臨界角。因此，當光以特定角度入射，兩個偏振將會被分開來。利用在液晶中摻雜光敏感偶氮染料，即可藉由照光來改變液晶秩序性，藉以調控入射光感受之有效折射率，達到切換此偏振分光鏡的分光功能。偶氮液晶染料―1205在紫光(λ = 404 nm)的照射下，其分子從反式(trans)變成順式(cis)，會擾動排列規律的液晶分子，使液晶介質層的折射率從原本的雙折射性(ne/no)變為各向同性(niso)，此時s波和p波經偏振分光鏡後的傳播路徑相同，即偏振分光功能被關閉。而在綠光(λ = 532 nm)的照射下，染料分子將從順式(cis)變為反式(trans)，液晶層的折射率將切換回雙折射性狀態，此時s波和p波經偏振分光鏡後便可分開至不同傳播方向。此一光控染料分子的型態變化為可逆的，且兩個狀態穩定時間長，皆可視為穩態，因此我們成功地製作出一可光切換且雙穩態的偏振分光鏡。此元件除了具可調控及節能的優點外，還能藉由照光區域的選擇來進行不同區域的調控，使得在往後的應用上元件設計更加簡單且富有變化。

Polarizing beam splitters (PBSs) split the orthogonal s and p polarizations of the incident light. They are of considerable importance in many optical systems including liquid crystal displays (LCDs), optical communications and optical storage devices. In this study, we aimed to design an active PBS by sandwiching a dye-doped liquid crystal thin layer (ne = 1.7126; no = 1.5287) between two high-index prisms (nprism = 1.778). The working principle of PBS is as follows: As a ray of light propagates from an optically denser medium to a rarer one at an angle larger than a particular critical angle, it is entirely reflected. Such phenomenon is called “total internal reflection”. The birefringence nature of the liquid crystal leads to different critical angles for s-wave and p-wave respectively. Thereby, at a certain angle, the incident light will be divided into two rays with different linear polarizations. In conjunction with an azobenzene dye, the orientational order of the liquid crystal can be optically controlled and so can the effective indices. Under violet irradiation (λ = 404 nm), the azo-dye 1205 experiences an isothermal transition from trans- to cis-state resulting in a phase transition from the nematic to isotropic state; whereas the back-isomerization process can be exerted by green irradiation (λ = 532 nm). Such switching is reversible and bistable. Hence, a photo-switchable and energy-conserving PBS was demonstrated. Moreover, this device can be locally addressed by a spatially modulated pump, which simplifies and enriches the design for further applications.

論文審定書 i
摘要 ii
Abstract iii
圖錄 vii
表錄 xii
第一章 緒論 1
第二章 液晶簡介 2
2-1液晶的發現 2
2-2何謂液晶 2
2-3液晶分類 3
2-3.1向列相 4
2-3.2膽固醇相 4
2-3.3層列相 7
2-4液晶的物理特性 9
2-4.1溫度對秩序參數的影響 10
2-4.2折射率異向性 11
2-4.3介電係數異向性 13
2-4.4彈性連續體理論 14
2-4.5黏滯係數 15
第三章 理論介紹 17
3-1折射定理(Snell’s law) 17
3-2 菲涅爾方程式(Fresnel equations) 18
3-3反射率和穿透率(Reflectance and Transmittance) 21
3-4全內反射(Total internal reflection) 23
3-5光致同素異構化反應(Photo–isomerization) 25
3-6光致等溫相變(Light–induced isothermal phase transition) 25
第四章 實驗設計與模擬 27
4-1選擇適合作為偏振分光鏡的稜鏡 28
4-1.1稜鏡折射率 28
4-1.2稜鏡形狀 30
4-2選擇適合作為偏振分光鏡的偶氮染料 34
4-3設計偏振分光鏡中液晶層之配向 35
4-3.1水平配向方式 35
4-3.2垂直配向方式 36
4-4計算在不同入射角θ1之T、R 37
4-5模擬液晶折射率改變過程中所對應之T、R 44
4-6液晶層厚度對偏振分光鏡之影響 46
4-7相變過程中出射光之位移或角度改變 48
第五章 實驗方法與過程 51
5-1比較光敏感材料之特性 52
5-1.1材料介紹 52
5-1.2藥品配製 54
5-1.3元件製作過程 54
5-1.4實驗架設 57
5-2光敏感材料之折射率量測 59
5-2.1元件製作過程 59
5-2.2實驗架設 61
5-3偏振分光鏡之特性量測 63
5-3.1元件製作過程 63
5-3.2實驗架設 63
第六章 實驗結果與討論 67
6-1光敏感材料之特性分析 67
6-1.1染料濃度對相變點的影響 67
6-1.2染料濃度對相變時間的影響 69
6-1.3激發光強度對相變時間的影響 73
6-1.4染料濃度對相變溫寬的影響 76
6-1.5染料濃度對在室溫下維持各向同性相之影響 77
6-2不同入射角對偏振分光鏡之影響 78
6-2.1 找出光敏感材料的折射率 78
6-2.2 找出適當的入射角範圍 80
6-3偏振分光鏡之光控特性分析 83
6-3.1照光切換相態過程中的偏振分光情況 84
6-3.2激發光之偏振對切換偏振分光鏡過程的影響 90
6-3.3連續切換偏振分光鏡測耐用性 94
6-3.4不同相態下之偏振分光程度 96
6-3.5偏振分光鏡之穩定性 101
6-3.6照光變化過程中光損耗原因 102
6-3.7偏振分光鏡在相變過程中之光強度振盪原因 105
第七章 結論 111
參考資料 113

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