透過聚合物穩固或動態散射機制製作散射式液晶波導元件;Scattering-type liquid crystal waveguide devices based on polymer stabilization or dynamic scattering mechanisms

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题名:	透過聚合物穩固或動態散射機制製作散射式液晶波導元件;Scattering-type liquid crystal waveguide devices based on polymer stabilization or dynamic scattering mechanisms
作者:	蔡沅璋;Tsai, Yuan-Chang
贡献者:	光電科學與工程學系
关键词:	液晶;liquid crystal
日期:	2023-08-11
上传时间:	2023-10-04 15:50:52 (UTC+8)
出版者:	國立中央大學
摘要:	本論文可分為兩大方向，第一部分主要使用液晶波導原理討論扭轉混成型結構之聚合物網絡型液晶盒(TH-PNLC)，利用側向光源饋入液晶盒，若未施加電場至TH-PNLC液晶盒，由於材料中向列型液晶分子與液晶聚合物折射率匹配，故入射光於液晶盒中進行全反射；而當施加電場至TH-PNLC液晶盒，由於材料中向列型液晶分子與液晶聚合物折射率產生不匹配，其入射光產生散射並由兩觀測面出射。此時觀察到兩道出射散射光之主要的偏振光分量具有差異，且若材料中摻雜光起始劑則此差異會增加，為了解此現象，我們透過探討聚合物網絡型液晶於光聚合後對TH結構的改變，以及於材料中摻雜光起始劑與未摻雜光起始劑之TH-PNLC液晶盒進行比較，探討其出射散射光偏振態的變化，並且以正向入射未偏振及線偏振光至未摻雜及摻雜光起始劑之TH-PNLC液晶盒，用於對比側向光源饋入液晶盒結果。接著統整上述所得結論，完整解釋當未偏振光自側向入射之TH-PNLC造成其兩側出射散射光偏振差異的原因；最後利用TH-PNLC結構非對稱特性之散射光製作單向光源液晶元件及隱私保護之應用。第二部分為使用負型液晶摻雜手性分子及離子並利用塗佈有PVK薄膜及垂直配向膜之ITO玻璃基板製成液晶盒，透過PVK薄膜能阻絕直流電場及照射紫外光後可形成良好導體的特性，結合液晶動態散射執行圖案化的工作，其中當外加高頻電場至液晶盒時，可將其切換至穿透態(平面態結構)，當關閉外加電場後，仍可持續維持於穿透態(平面態結構)；然而利用低頻或直流電場便可將穿透態切換至散射狀態(焦錐態結構)，同樣關閉外加電場後，仍可持續維持於散射態(焦錐態結構)。而由於PVK薄膜特性，可藉由光罩將液晶盒區分出受紫外光照射的區域，當開啟直流電場及紫外光即可使液晶盒同時具有散射態的文字圖案及其餘穿透態的透明區域，並透過將側向光源饋入寫上圖案之液晶盒，即可利用液晶波導的原理，入射光於穿透態區域中因折射率連續而進行全反射使其觀側面無出射光；而於散射態之文字區域則因折射率不連續使文字圖案產生出射光，進而提高液晶盒整體對比度。 ;The research topics in this thesis include the following two sections. The first section focuses on the applications of the liquid crystal (LC) waveguide effect to discuss the fabrications of twisted hybrid polymer network LC (TH-PNLC) structures. When an edge light source is fed into the LC cell and no electric field is applied to the TH-PNLC cell, the refractive indices of the nematic LCs and the LC polymer are matched. As a result, the incident light undergoes total internal reflection within the LC cell. However, when an electric field is applied to the TH-PNLC cell, the refractive indices of the nematic LCs and the LC polymer become mismatched. This mismatch causes the incident light to scatter and emit from the two observation surfaces of the LC cell. When observing the scattered light emitted from the two surfaces, there is a difference in the main polarization components of the scattered light from the two substrates. Additionally, if the material is doped with a photoinitiator, this difference in polarization components will increase. To understand this phenomenon, we investigate the changes in the TH structures after photopolymerization and the variations in the polarization states of the scattered light from the TH-PNLC cell without doping and with doping of the photoinitiator in the material. Input unpolarized and linearly polarized light to TH-PNLC cells without doping and with doping of the photoinitiator, respectively, the different results of feeding side light sources into the two LC cells are obtained. In summary, the obtained results explain the reasons for the polarization differences in the scattered light emitted from the sides of the TH-PNLC when unpolarized light is incident from the side. Finally, the asymmetric scattering property of the TH-PNLC structure is utilized to demonstrate unidirectional LC light source devices and privacy protection applications. In the second section, negative-type LCs doped with chiral dopants and ions are used to demonstrate an LC cell fabricated by two ITO glass substrates coated with a PVK film and a vertically aligned film. By utilizing the PVK film′s ability to block DC electric fields and its property of forming a good conductor when exposed to ultraviolet light, it is possible to obtain pattern addressing work using dynamic scattering of LCs. When a suitable high-frequency electric field is applied to the LC cell, it can be switched to a transparent state with planar textures. Even after the external electric field is turned off, it can still maintain the transparent state with imperfect planar textures. However, by applying a low-frequency or DC electric field, the transparent state can be switched to a scattering state with focal conic textures via dynamic scattering. Similarly, even after the external applied electric field is turned off, it can maintain the scattering state (focal conic textures). Due to the characteristics of the PVK film, the LC cell can be divided into two regions exposed to ultraviolet light using a photomask. When a DC electric field and ultraviolet light are applied simultaneously, the LC cell can exhibit a scattering state for text patterns and transparent regions for the rest. When an edge light source is fed into the LC cell with the addressed pattern, the principle of the LC waveguide is utilized to display the contrast. Incident light in the transparent region undergoes total internal reflection due to the continuous refractive index, resulting in no light being emitted from the side view. However, in the scattering region with the addressed pattern, the discontinuous refractive index causes the patterns to emit light, thereby enhancing the overall contrast of the LC cell.
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