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系統識別號 U0026-1808201415274200
論文名稱(中文) 液晶結合微奈米溝槽結構於可調控預傾角及分佈式回饋雷射之研究與應用
論文名稱(英文) Investigations on tunabilities of pretilt angle and distributed feedback laser based on liquid crystal cells incorporating with micro- and nano-grooves of polymer
校院名稱 成功大學
系所名稱(中) 光電科學與工程學系
系所名稱(英) Department of Photonics
學年度 102
學期 2
出版年 103
研究生(中文) 游凱宇
研究生(英文) Kai-Yu Yu
學號 l78971136
學位類別 博士
語文別 英文
論文頁數 59頁
口試委員 指導教授-李佳榮
共同指導教授-郭啟東
召集委員-黃啟炎
口試委員-黃宣瑜
口試委員-羅光耀
中文關鍵字 表面起伏光柵  微溝槽結構  光膨脹效應  液晶  預傾角  分佈式回饋雷射  可調控雷射 
英文關鍵字 surface relief grating  micro-grooved structure  photo-expansion effect  liquid crystal  pretilt angle  distributed feedback laser  tunable laser 
學科別分類
中文摘要 本論文旨在探討液晶結合溝槽結構於可調控光電元件的應用。論文題目為「液晶結合微奈米溝槽結構於可調控預傾角及分佈式回饋雷射之研究與應用」,分為兩大主題,茲說明如下:
(1) 第一個主題為「微溝槽結構之形成用予調控液晶分子預傾角」。本研究利用脈衝雷射全像干涉法於具有垂直配向單元之具偶氮染料摻雜之高分子薄膜上製作次微米溝槽結構,藉由調整干涉光場寫入時間實現不同深淺之微溝槽結構。實驗發現,隨著溝槽深度增加,液晶分子與基板表面之夾角呈現遞減趨勢,此現象乃溝槽產生之水平錨定力及覆蓋溝槽上方之垂直配向層之垂直配向力之間錨定力相互競爭所致。液晶分子所受的表面錨定能與溝槽深度呈平方正比關係,因此隨著寫入時間的增加,其所引致的水平錨定力亦隨之增加。當寫入時間由0秒增加至25秒,預傾角可由初始的89°下降至18.3°,將近70°的調控範圍。
(2) 第二個主題為「利用奈米壓印法製作奈米等級之聚合物溝槽結構於熱調控液晶分佈式回饋雷射之應用」。本研究利用奈米壓印法製作奈米等級之聚合物溝槽結構,並於溝槽結構上方引入摻雜有雷射染料之向列型液晶以達成可熱調控波長之分佈式回饋雷射。此奈米等級溝槽為二階布拉格光柵,因此具有面出射雷射輸出之特性。因雷射輸出波長與液晶折射率有關,因此可藉由改變液晶層之溫度來達成調控雷射波長之目的。實驗上,當溫度由10 °C 增加至 50 °C時,雷射波長將由625.1 nm藍移至606.35 nm,此乃液晶層之非尋常折射率隨溫度上升而下降所致。
英文摘要 This thesis, entitled “Investigations on the tunability of pretilt angle and distributed feedback laser based on liquid crystal cells incorporated with micro- and nano-grooves of polymer,” examines the tunability of liquid crystal (LC)-based optical devices with a grooved structure. The following two topics are discussed.
(1) Controllable pretilt angle of LCs with the formation of microgrooves. This work investigates the controllability of the pretilt angle of LCs in a cell with an initial vertical alignment through microgrooves induced by the holographic fast-writing method. By changing the writing time or intensity of the pumped beam, the microgrooves with various surface modulations can form and provide distinct planar anchoring strength for the LCs. The pretilt angle of the LCs can be controlled from 18.3° to 89°. The writing time of the microgrooves takes less than 25 s, which is a two-fold reduction in the time taken in previous investigations using other photoalignment methods.
(2) Thermally tunable LC distributed feedback laser based on a polymer grating with nanogrooves fabricated by nanoimprint lithography (NIL). This work demonstrates a thermally tunable dye-doped liquid crystal (DDLC) distributed feedback (DFB) laser based on a polymer grating. The surface emitting the DDLC DFB laser is supported by the second-order Bragg grating with nanogrooves with periodicity of 360 nm and pre-fabricated by UV NIL. The lasing wavelength of the DFB laser can be tuned from 625.1 nm to 606.35 nm if the temperature increases from 10 °C to 50 °C. The tunability of the laser is attributable to the temperature-sensitive feature in the effective refractive index of the LCs.
論文目次 摘要.......................I
Abstract..................II
Acknowledgements..........IV
Contents...................V
List of Figures.........VIII
List of Tables..........XIII
CHAPTER 1 Introduction...................................................1
CHAPTER 2 Introduction to Liquid Crystals................................3
2.1 What is Liquid Crystal.....................................................3
2.2 Classification of Liquid Crystals..........................................4
2.2.1 Smectic Phase............................................................4
2.2.2 Nematic Phase............................................................5
2.2.3 Cholesteric Liquid Crystal...............................................6
2.3 Physical Properties of Liquid Crystals.....................................7
2.3.1 Order Parameter..........................................................7
2.3.2 The Anisotropy...........................................................8
2.3.3 Dielectric Anisotropy....................................................8
2.3.4 Optical Anisotropy......................................................10
2.3.5 Surface Alignments......................................................12
2.3.6 Pretilt Angle...........................................................13
2.3.7 Elastic Continuum Theory................................................14
2.3.8 Temperature Effect on NLC...............................................15
CHAPTER 3 Azobenzene Thin Film..........................................17
3.1 Photoisomerization of Azobenzenes.........................................17
3.2 Photo-Expansion Effect....................................................19
CHAPTER 4 Theoretical Background........................................21
4.1 Laser-Induced Gratings....................................................21
4.2 Groove Theory: Berreman’s Model..........................................22
4.3 Surface Anchoring Energy..................................................24
4.4 Distributed Feedback Structure............................................26
4.4.1 Principle of Bragg grating..............................................26
4.4.2 Diffraction Grating Equation............................................28
4.4.3 Couple Wave Theory......................................................29
CHAPTER 5 Controllable pretilt angle of liquid crystals with the formation of microgrooves..................................................................32
5.1 Introduction..............................................................32
5.2 Experimental Setup and Materials..........................................33
5.3 Results and Discussion....................................................36
CHAPTER 6 Thermally tunable liquid crystal distributed feedback lasers..42
6.1 Introduction..............................................................42
6.2 Sample Fabrication and Experimental Setup.................................43
6.3 Results and Discussion....................................................47
CHAPTER 7 Conclusion and Prospection....................................53
7.1 Conclusion................................................................53
7.2 Prospection...............................................................54
References....................................................................55
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