Characteristics and application of polymer dispersed liquid crystal in head up display and tunable resonant cavity

液晶材料已被研究許久且應用在許多方面上，然而普通顯示器用的水平、垂直配向液晶等仍需要用到偏光片，這使得背光源的使用效率低。為了克服此問題，高分子聚合物分散液晶這種由液晶和高分子聚合物單體所組成的材料孕育而生。高分子聚合物分散液晶因其特殊的光電特性，不需要用到偏光片。此外，高分子聚合物分散液晶有著高對比跟不錯的反應時間，因此把高分子聚合物分散液晶應用在抬頭顯示器以及可調式共振腔上是可行的。 在論文第前三部分中，首先介紹液晶、製作過程以及針對高分子聚合物分散液晶本身特性以及各個可調參數作探討。例如: 液晶濃度、液晶盒厚度、照射紫外線強度…等。同時分析各個數據的優劣，並找出最適合應用在抬頭顯示器以及可調式共振腔的參數。 本論文第四部分利用前面所找出最適當的參數製作高分子聚合物分散液晶，應用在抬頭顯示器上。由於高分子聚合物分散液晶本身的良好特性，使得我們的抬頭顯示器可以有極高的光使用效率以及有高的對比。另外我們採用超高亮度LED模組當作背光源，以達到大白天也能看見清晰的影像的要求。 本論文第五部分則是利用高濃度的高分子聚合物單體所調製的高分子聚合物分散液晶來製作法布立－培若共振腔。我們想利用本身穿透率高、折射率可調以及反應速度快的特性，在共振腔內藉由給予不同的電壓來改變特定波長的穿透率(波長調變)，來彌補對比不足的缺點。Liquid crystal (LC) material has been investigated for a long time and has been applied to a variety of device. However, most of display, which uses vertical and planar alignment liquid crystal, still needs to utilize the polarizer. The light efficiency of back light source may suffer a lot from polarizer. In order to overcome this kind of problem, polymer dispersed liquid crystal (PDLC) which consists of monomer and liquid crystal was invented. Due to the unique E-O characteristics of PDLC, it doesn’t need polarizer to block the polarized light. Moreover, PDLC has high contrast ratio (CR) and quick response time. It’s feasible to apply polymer dispersed liquid crystal to head-up display (HUD) and tunable resonant cavity. In chapter 1 and 2, we introduced the liquid crystals and fabrication process of PDLC. In chapter 3, we studied the characteristics of PDLC and the influence of parameters such as LC/polymer concentration, cell gap and UV intensity on PDLC. By comparing with the result of different parameters, we can obtain the most suitable parameter for fabricating head-up display and tunable resonant cavity. In chapter 4, we applied the PDLC to HUD display application by using the optimized parameter that we found in the first part. Because of the good characteristics of PDLC, it can present high CR and high light efficiency. We also used the ultra-bright LED as a back light source so that the projected image can also be seen clearly in broad daylight. In chapter 5, we utilized high polymer concentration PDLC to fabricate the tunable Fabry-Perot resonant cavity. Due to its high transmittance, tunable refractive index and fast response time, it can achieve wavelength tuning (or change transmittance for certain wavelength) in resonant cavity by giving different voltage. By using this method, it can help increasing contrast ratio.中文摘要 i Abstract ii List of Figures vi List of Tables viii Chapter 1: Introduction 1 1.1 Introduction of Liquid Crystal 4 1.1.1 The Classification of Liquid Crystal 5 1.1.2 Liquid crystal Alignment 7 1.1.3 Liquid Crystal Physical Properties 7 1.1.4 Liquid Crystal/Polymer Composites 9 1.2 Polymer Dispersed Liquid Crystal 10 1.2.1 Operation principle of PDLC 10 1.2.2 Method of PDLC fabrication 13 Chapter 2: Experiment preparation 14 2.1 Preparation of the PDLC films 14 2.1.1 Preparation of LC/polymer material 14 2.1.2 Fabrication of PDLC cells 15 2.2 Experimental set-up for electro-optical measurements 16 2.2.1 Experimental set-up for transmittance-voltage curve 16 2.2.2 Experimental set-up for response time 18 Chapter 3: The studies of characteristics of PDLC 19 3.1 Studies of LC/polymer concentrations 19 3.2 Studies of PDLC cell gap 22 3.3 Studies of UV exposure intensity 27 3.4 Studies of UV exposure time 29 Chapter 4: Application of PDLC in head-up display 31 4.1 Introduction of head-up display 31 4.2 Experimental set-up and preparation for HUD 33 4.2.1 Experimental set-up of HUD 33 4.2.2 Preparation of image source generator 34 4.3 Experiment results and discussion 37 4.4 Conclusion 48 Chapter 5: Application of PDLC in tunable resonant Fabry-Perot cavity 49 5.1 Introduction of Fabry-Perot Etalon 49 5.2 Purpose of combining nano-PDLC with Fabry-Perot 52 5.3 Preparation of Fabry-Perot Etalon cavity 53 5.3.1 Fabricating Fabry-Perot cavity by coating Al 54 5.3.2 Fabricating Fabry-Perot cavity by coating Ag 55 5.3.3 Fabricating Fabry-Perot cavity by coating SiO2/TiO2 56 5.4 Experiment results and discussion 60 5.4.1 50% polymer PDLC Fabry-Perot cavity 61 5.4.2 60% polymer PDLC Fabry-Perot cavity 63 5.4.3 70% polymer PDLC Fabry-Perot cavity 65 5.4.4 75% polymer PDLC Fabry-Perot cavity 67 5.5 Conclusion 69 Chapter 6: Conclusion and future work 71 Reference 7