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系統識別號 U0026-1002201716405200
論文名稱(中文) 全像膽固醇液晶模板於具圓偏振暨波段選擇性光柵之研究與應用
論文名稱(英文) Circular-polarization and wavelength selective gratings based on polymer templates of holographic cholesteric liquid crystal
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 105
學期 1
出版年 106
研究生(中文) 鄭揚臣
研究生(英文) Yang-Chen Zheng
學號 L76034297
學位類別 碩士
語文別 英文
論文頁數 68頁
口試委員 口試委員-李偉
口試委員-羅光耀
口試委員-莫定山
指導教授-李佳榮
中文關鍵字 膽固醇液晶模板  全息光柵  繞射元件  圓偏振選擇性 
英文關鍵字 cholesteric liquid crystal polymer template  holography gratings  diffraction elements  circular polarization selectively 
學科別分類
中文摘要 本篇論文成功的利用雙光干涉的技術製備出具有圓偏振與波段選擇性之膽固醇液晶模板光柵。利用膽固醇液晶模板(洗掉/回灌)的技術,回灌不同旋性及不同反射波段的膽固醇液晶於右旋膽固醇液晶模板光柵中,因為模板區與非模板區具有不同的反射波段,當偵測光波長落在回灌的膽固醇液晶反射波段(非模板區反射波段)內時,會有振幅型光柵的效果。實驗還發現,在製作膽固醇液晶模板光柵的曝光過程中會產生非本實驗所需的二維結構,此二維結構的形成會降低本研究製作的一維光柵的繞射效率,為了得到良好的一維光柵,需要控制曝光劑量以避免二維光柵的形成。
本論文探討了此膽固醇液晶模板光柵在回灌不同膽固醇液晶材料後之特性,包含其適用的波長與偏振狀態。由於此元件是利用膽固醇液晶對圓偏振光的選擇性反射特性所製作,因此在回填不同旋性及反射波段的材料後,會對特定波段的左圓偏振光和右圓偏振光產生不同的繞射效率。也就是說,此元件具有圓偏振選擇性、波段選擇性,以及穿透與反射雙操作模式等特點。此外,此元件的繞射強度還可以利用電場調控。當施加電場時,樣品內的膽固醇液晶變成焦錐態,此時因散射很強而使穿透光的繞射強度降低。反之,釋放電場後,膽固醇液晶會從焦錐態回到平面態,繞射強度也會回復到未加電場前的狀態。因此,這種基於膽固醇液晶模板技術所開發的光柵可以應用於光學繞射元件。
英文摘要 In this study, a cholesteric liquid crystal (CLC) template grating with circular polarization and wavelength selectivity is successfully fabricated by two-beam interference. The grating is fabricated by use of CLC template (washing out/refilling) technology and refilling CLCs with different handedness and reflection band. When the wavelength of a probe beam is in the CLC reflection band (reflection band of the non-template region), the device works as an amplitude grating because the template and non-template regions reflect distinct wavelengths. During the fabrication of the CLC template grating, the UV light exposure produces two-dimensional (2D) structures in the sample. The formation of the 2D structure reduces the diffraction efficiency of the CLC template grating. The exposure UV dose is controlled to avoid the formation of the 2D grating and thus obtain a good one-dimensional (1D) grating.
Experimental results show that the circular polarization and wavelength selectivity of the CLC template grating can be achieved by refilling different CLCs. This principle is based on the selective Bragg reflection characteristic of CLC. The Bragg reflection not only allows the CLC template grating to produce diffracted light of a specific wavelength but also provides the CLC with circularly polarized selective characteristics. As different CLCs are refilled in CLC template gratings, different diffraction efficiencies appear for left-hand circularly polarized and right-handed circularly polarized (LCP and RCP, respectively) lights. The beam steering element exhibits circular polarization selectivity and dual operation modes. The diffraction intensity can be electrically controlled. When the electric field is applied, the arrangement of the CLC becomes in a focal conic state, which presents strong scattering such that the diffraction intensity decreases. However, after releasing the electric field, CLC reorients from the focal conic state to the planer state and the diffraction intensity returns to its original state. Therefore, this CLC-based device can be potentially used for applied diffraction elements in optics.
論文目次 摘要 I
Abstract II
Acknowledgements IV
Contents V
List of Figure VIII
List of Table XII
Chapter 1 1
Chapter 2 3
2.1 Introduction to Liquid Crystals 3
2.2 Classification of Liquid Crystals 4
2.2.1 Lyotropic Liquic Crystals 4
2.2.2 Thermotropic Liquic Crystals 4
2.3 Physical and Electro-optic Properties of Liquid Crystals 8
2.3.1 Optical birefringence 8
2.3.2 Dielectric Anisotropy 11
2.3.3 Elastic Continuum Theory of Liquid Crystals 12
Chapter 3 13
3.1 Optical Properties of Cholesteric Liquid Crystals 13
3.2 Factors Influencing on Helical Pitch of Cholesteric Liquid Crystal 14
3.2.1 Temperature 14
3.2.2 Magnetic and Electric Fields 15
3.2.3 Optical Field 17
3.3 Cholesteric Liquid Crystal Polymer Templates 17
3.3.1Backgrounds of Cholesteric Liquid Crystal Polymer Templates 17
3.3.2 Fabrication of LC polymer template 18
Chapter 4 20
4.1Principle of Holography 20
4.2Laser-induced Holographic Grating 22
4.3Category of Gratings 28
4.4Diffraction Theory in Thin Transmission Grating 30
4.5Laser-Induced Intensity Gratings in LC/prepolymer Composite Films 35
Chapter 5 38
5.1Materials 38
5.1.1 CLC Polymer Templates 38
5.1.2 Materials of Refilled 41
5.2 Fabrication of Sample 42
5.2.1 Preparation of Glass Substrates 42
5.2.2 Fabrication of Empty Cells 43
5.2.3 Mixture for Fabrication of Single CLC Polymer Template 43
5.2.4 Manufacturing CLC-refilled CLC Polymer Template Sample 45
5.3 Experimental Setups 46
5.3.1 Setup for Two-beam Interference Technique 46
5.3.2 Setup for Measuring the Intensity of First Order Diffraction 47
Chapter 6 49
6.1 Factors for Performing Grating: Curing Condition 49
6.2 Factors for Performing Grating: Refilled Materials 52
6.3 Factors for Performing Grating: Period of CLC Template 58
6.4 Electrically Controllable Diffraction 61
Chapter 7 64
7.1 Conclusion 64
7.2 Future Works 64
List of Reference 65

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