投影電視用反射式液晶光閥之評估與探討

Abstract

本論文主旨在探討如何利用電腦模擬來評估液晶顯示器的光學品質， 以得到最佳 的製作參數組合，使得投影電視用反射式液晶光閥之性能 可以達到高亮度、高對比度 、低色差的要求，並藉由此最佳製作參數 組合製作單一獨立畫素的液晶盒樣品，量測 其光電特性。另外，我們 從液晶連續體彈性形變理論與瓊斯矩陣(Jones Matrix)著手 模擬液晶 顯示器的光電特性，然後比較模擬與實驗的結果。 在本論文中，我們為了分析扭轉向列型顯示模式的光學品質，利用電腦模 擬建立 不加電壓狀態時之二維參數空間光學品質評估圖；同時為了分 析Reflective Chiral Homeotropic(RCH)顯示模式的光學品質，我們 也用電腦模擬來建立新型加上電壓狀態 時之二維參數空間光學品質評 估圖。經由我們的電腦模擬和實驗證明RCH 液晶盒其正 向方向的對比 度、響應速度、光效率等光學品質皆有優良的表現。而在色散特性方面 ，與電控雙折射率(ECB)顯示模式相比，RCH液晶盒對波長也較不敏感，但 還不能達到 真正的無色差的純中性色表現。 為進一步改善三片液晶光閥式投影電視的色差問題，我們使用Multi- twist和 Multi-β的方法，經由模擬和實驗結果得到驗證，確實可 使紅、綠、藍三色光具有相 同的光電特性曲線，在相同驅動電路下， 可使三片式投影系統達到最高光調變效率及 最佳色彩平衡。 The aim of this thesis is to evaluate the optical properties of reflective- type liquid crystal displays (RLCDs), especially, for the applications in projection display. We have investigated the methodology and found the optimized operation conditions of RLCDs, by using a computer simulation, to meet the requirement of high brightness, high contrast ratio, and low color dispersion. LC cells of single pixel were also fabricated and its electro-optical (EO) performance was measured and compared to the simulation one. In the computer simulation,we have created two-dimensional (2D) parameter space diagrams to analyze the influence of the twist angle, natural retardation, and polarizer angles on the optical properties of reflective twisted- nematic (RTN) modes at voltage-off state. It was found that the brightness of a conventional 45° TN cell can be enhanced by changing the polarizer angle to -10°. Similar diagrams were also established for a Reflective Chiral Homeotropic (RCH) mode, while biasing at different voltages. The best parameters of a RCH mode can be easily obtained from these diagrams to optimize the brightness and the contrast ratio at the same time. However, a real colorless appearance for all gray levels still can not be obtained. The color balance of a projection display using three LCD light valves can be further improved by employing multi-twist and multi-polarization method. The twist and the polarization angles of RLCD panels for red, green, and blue light, respectively, can be adjusted individually to obtain the same EO characteristics. Excellent performances of balanced color, high brightness, and high contrast ratio have been confirmed by the computer simulation as well as the experimental results.