| 摘要: | 本論文研究分為三個部分，第一部分聚焦於利用90°扭轉向列型液晶(90°-twisted nematic liquid crystals，簡稱90°-TNLCs)製作之可連續電控液晶線偏振旋轉器的光電特性探討。當液晶盒厚度(d)、光學異向性(Δn)及入射光波長(λ)滿足特定條件(1.27 < dΔn / λ < 1.7)且以線偏振光入射時，對液晶盒施加不同的外加電場可實現連續的線偏振旋轉效果。由實驗及模擬結果得知，電控單一90°扭轉向列型液晶盒其出射光之偏振旋轉角(polarization rotation angle，簡稱PRA)可得到從93°連續旋轉至0°的變化，且在偏振旋轉過程中，出射光線偏振度(degree of linear polarization，簡稱DoLP)均保持在0.95以上。此外，為驗證只要滿足特定的dΔn/λ條件即可實現穩定的連續電控線偏振旋轉。本部分研究亦展示了不同液晶材料、入射光光源及液晶盒厚度之量測與模擬結果。最後，基於本研究團隊先前提出的串聯扭轉向列型液晶盒架構所製成的偏振旋轉器，我們進一步利用電控串聯兩片90°扭轉向列型液晶盒，使其出射線偏光之PRA可實現連續旋轉180°的效果，且無需考慮入射線偏振光的偏振方向。本論文之第二部分主要探討在90°-TNLCs中摻雜二色性染料(dichroic dye)對電控線偏振旋轉特性之影響。當二色性染料摻雜於扭轉向列型液晶中時，染料分子會根據賓主效應(guest–host effect)而隨液晶分子共同排列。利用二色性染料其偏振選擇性吸收之特性，可有效吸收非必要之偏振光分量，用以提升出射光之DoLP，進一步優化電控線偏振旋轉效果。此外，本部分亦深入分析摻雜二色性染料的90°扭轉向列型液晶對光的吸收特性，並與水平配向液晶(homogeneous alignment LCs，簡稱HALCs)的吸收行為進行比較討論。最後，由於所使用之材料具備吸光特性，本部分亦針對液晶盒的穿透度光譜進行探討。本論文之第三部分將第一部分的研究成果延伸至二維空間，利用在90°-TNLCs中摻雜液晶單體(LC monomer)，透過階段性地施加不同外加電場並同時照射紫外光之方式，製作聚合物網絡90°扭轉向列型液晶(polymer network 90°-TNLCs，簡稱PN-90°-TNLCs)元件，以達成在空間中形成具不同液晶排列之區域分布。當線偏振光入射此液晶元件之不同位置時，其出射光呈現在空間上有不同的PRA分布。此外，以第一部分之可連續電控液晶線偏振旋轉器為基礎，透過模擬方式提出光束整形(beam shaping)的應用概念，展示當高斯光束(Gaussian beams)通過像素化之90°-TNLCs元件後，藉由控制元件內各像素之液晶排列並適當地搭配偏振片，即可將原本的高斯強度分布整形成具平坦化強度分布的輸出光束。;The research in this thesis is divided into three parts. The first part focuses on investigating the electro-optical properties of an electro-tunable linear polarization rotator fabricated based on 90°-twisted nematic liquid crystals (90°-TNLCs). When the LC cell thickness (d), optical anisotropy (Δn), and wavelength of the incident light (λ) lie in a specific relationship (1.27 < dΔn/λ < 1.7), continuous linear polarization rotation can be achieved through the application of external electric stimuli. Experimental and simulation results demonstrate that a single 90°-TNLC cell enables a continuous polarization rotation angle (PRA) ranging from 93° to 0°, maintaining a high DoLP exceeding 0.95 throughout the rotation process. To further confirm that stable electro-tunable linear polarization rotation can be consistently obtained under the specified dΔn/λ conditions, measurements and simulations utilizing various LC materials, incident light sources, and LC cell thicknesses are presented. Finally, building upon the previously proposed tandem TNLC polarization rotator developed by our research group, this study further proposes an advanced electrically tunable polarization rotator composed of tandem-180°-TNLC cells composed of two 90°-TNLC cells. This configuration successfully achieves continuous PRA rotation up to 180°, independent of the incident linear polarization orientation. The second part of this thesis explores the influence of dichroic dye doping in 90°-TNLCs on electro-tunable linear polarization rotation performance. When dichroic dyes are doped into the 90°-TNLC cell, the dye molecules align with the LC molecules through the guest–host effect. Due to the anisotropic absorption characteristics of the dichroic dyes, unnecessary polarization components of the transmitted light can be effectively absorbed, thus enhancing the output DoLP and optimizing the linear polarization rotation properties. Moreover, this part provides an in-depth analysis of the absorption properties of dye-doped 90°-TNLCs, including a comparative study between these properties and those exhibited by homogeneous alignment LCs (HALCs). Additionally, considering that the employed dye materials inherently possess absorptive characteristics, this part also examines the spectral transmittance properties of the proposed LC cells. The third part of this thesis extends the research findings from the first part into a 2-D linear polarization distribution. By doping LC monomers into the 90°-TNLCs and sequentially applying varying electric voltages combined with simultaneous UV exposure, a polymer network-90°-TNLC (PN-90°-TNLC) cell with partitioned LC alignment distributions is fabricated. This LC device produces spatially varying output PRAs when linearly polarized light is incident at different positions on the PN-90°-TNLC cell. Furthermore, a beam-shaping concept is introduced and demonstrated through simulation based on the pixelization of the electro-tunable linear polarization rotator proposed in the first part. By precisely controlling the LC alignment distribution within each pixel of the proposed 90°-TNLC device and integrating appropriate polarizers, an incident Gaussian beam can be effectively reshaped into an output beam exhibiting a flattened intensity profile. |
