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研究生： 林威良
Lin, Wei-liang
論文名稱： 結合史托克參數法與基因演算法對扭轉向列型 液晶盒進行多參數之量測
Combining Stokes Parameters Method and Genetic Algorithm for Measuring the Cell Thickness, Twist Angle, Pretilt Angle, and Azimuth Angle of Twisted-Nematic Liquid Crystal Cells
指導教授： 羅裕龍
Lo, Yu-lung
學位類別： 碩士
Master
系所名稱： 工學院 - 機械工程學系
Department of Mechanical Engineering
論文出版年： 2008
畢業學年度： 96
語文別： 英文
論文頁數： 108
中文關鍵詞： 扭轉角 、預傾角 、扭轉向列型液晶 、基因演算法 、史托克參數 、方位角 、厚度
外文關鍵詞： genetic algorithm, cell thickness, azimuth angle, pretilt angle, stokes parameters, twisted-nematic liquid crystals., twist angle
相關次數： 點閱：142  下載：2 
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    • 以往的研究中，史托克參數法常用於量測扭轉向列型液晶的各項參數。在這裡我們提出了一個方法，結合史托克參數法與基因演算法可計算出扭轉向列型液晶盒內的厚度、扭轉角、預傾角與方位角。對扭轉向列型液晶而言，其入射面液晶分子長軸方向與實驗座標X軸所夾的角度，可稱之為方位角。不同於過去文獻中在量測扭轉向列型液晶的各項參數時，皆受限於精確的初始方位角，而我們所提出的方法不需要事先知道精確的方位角，這就表示我們可以在任意的方位角下計算出扭轉向列型液晶盒內的厚度、扭轉角與預傾角，並且我們採用不同的線性偏振光當作我們的入射光源，經實驗證實也可取代多波長光源。
    當線性偏振光穿透液晶盒之後，由於扭轉向列型液晶具有光學異向性和旋光性，原本的線性偏振態會發生改變。我們利用光學實驗架構與史托克偏光儀量測線性偏振光經過液晶盒之後的穿透光強度，並藉由史托克偏光儀將所量測到的穿透光強度快速轉換為史托克參數。最後，我們利用基因演算法計算在不同方位角下扭轉向列型液晶盒內的厚度、扭轉角與預傾角。

    Here, we proposed a method that combining stokes parameters method and genetic algorithm for measuring the cell thickness, twist angle, pretilt angle and azimuth angle of twisted-nematic liquid crystal cells. The Jones matrix of the TN cell rotated around the axis parallel to the cell surface and perpendicular to the ray direction is derived here. Unlike the existing methods, they need to know the alignment directions of liquid crystal molecules at the cell substrates or provide multiple wavelengths. We can measure cell parameters in the TNLC cell at any degree of the azimuth angle without adjusting the azimuth angle to be a known value. Instead of multiple wavelengths, we choose horizontal linear polarized light and linear polarized light at 45 degree with respect to the x-axis as our input light.
    The cell thickness, twist angle, pretilt angle and azimuth angle of twisted-nematic liquid crystal (TNLC) can be determined by genetic algorithm. As the results of the experimental data, the maximum standard deviations of the cell thickness Δd=0.0074μm, twist angle Δψ=0.1867 degree, pretilt angle Δθp=0.3457 degree and azimuth angle Δα=0.1648 degree at the azimuth angle α=90 degree. The maximum standard deviations of the cell thickness Δd=0.0084μm, twist angle Δψ=0.1982 degree, pretilt angle Δθp=0.3382 degree and azimuth angle Δα=0.1521 degree at the azimuth angle α=0 (180) degree.

    中文摘要 .....I Abstract .....II 誌謝 .....III Table of Contents .....IV List of Figures .....VII List of Tables .....XI Chapter 1 Introduction .....1 1.1 Preface .....1 1.2 Review measurements of Twisted-Nematic Liquid Crystal Cells .....2 1.2.1 Optical measurement method .....2 1.2.2 Optical measurement method with Stokes parameters .....4 1.3 Destinations and motivations of the research .....6 1.4 Overview of chapters .....7 Chapter 2 Introduction of Liquid Crystals .....13 2.1 Structure of liquid crystal cells .....13 2.2 Alignment of liquid crystal molecules .....14 2.3 Twist effect of liquid crystal cells .....16 2.4 90 degree TN cell .....17 Chapter 3 Optical Properties of a TNLC cells .....24 3.1 Light propagation in homogeneous uniaxial LC materials .....24 3.2 Condition of Mauguin limit .....26 3.3 Operation principle of TN LCD .....27 3.4 Jones matrix of TNLC cells .....28 3.5 Poincar sphere .....32 Chapter 4 Measuring System and Methods .....39 4.1 Refractive indices of LC using E7 .....39 4.2 Basic theory of measuring method .....40 4.3 Genetic Algorithm preliminaries and process .....45 4.3.1 Error function of Genetic Algorithm .....50 4.4 Flow chart in procedure of Stokes parameters using Genetic Algorithm .....52 Chapter 5 Experimental Results and Analysis .....61 5.1 Simulations of the Stokes parameters method .....61 5.1.1 Choose input light : linear polarized light or right-hand circular polarized light .....61 5.1.2 Simulation of the Stokes parameters method : multiple linear polarized light .....63 5.1.3 Simulation of the Stokes parameters method : rotating the test cell .....64 5.1.4 Simulation of the Stokes parameters method : combining multiple linear polarized light and rotating the test cell .....66 5.2 Experimental results .....67 5.2.1 Determine the cell parameters at azimuth angle α = 90 degree .....68 5.2.2 Determine the cell parameters at azimuth angle α = 0 (180) degree .....70 5.3 Error analysis .....72 5.4 Varieties of stokes parameters at low pretilt angle .....73 Chapter 6 Conclusions and future works .....100 6.1 Conclusions .....100 6.2 Future works .....102 References .....103 Autobiography .....108

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