Design of the broadband retarders for 3D display

寬頻譜相位延遲片被廣泛運用在液晶顯示器，傳統撥放2D內容的液晶顯示器，寬頻譜相位延遲片是用於提高顯示器之對比值，觀者不需要配戴偏振眼鏡，所以過去有關寬頻譜的設計都不需考慮觀者頭偏的情形，也就是說，不需要考慮隨觀者頭偏而旋轉的檢偏器與補償用的相位延遲片。在利用偏振原理的3D立體顯示器統中，寬頻譜相位延遲片是用來將線偏振光轉成圓偏振光，利用圓偏振光降低觀者頭偏對影像品質的影響。隨著觀者頭偏角度的改變，可看出傳統評價指標-相位延遲量(phase retardation)與穿透率之間並沒有直接的關係，也就是此傳統評價指標不適用於立體顯示器。 在本論文中，我們提出三種評價指標，以針對寬頻譜相位延遲片的性能進行量化討論，這三個指標包括交互干擾 (crosstalk)、色差 (color-shift)、亮度比值 (luminance ratio)並且依各個頭偏角度值的總與，來評價寬頻譜相位延遲片。 藉由各個指標所得到的優化結果與液晶顯示器用之解析解比較，本論文所設計的優化結果在白光交互干擾有26.17% 的改善率 (improvement ratio)、紅光色差有38.55%之改善率、綠光色差有21.1%的改善率。 另外，亦以數值方法對各種層數、材料、架構、角度進行分析。得到當頭偏角度為90度時，其白光的交互干擾與色差分別為：單層的交互干擾會小於0.015相對應的色差會小於0.014；雙層的交互干擾會小於0.0007相對應的色差會小於0.001；三層的交互干擾與色差皆會小於0.00004 最後，由於傳統設計方法只針對在550 nm附近作優化，設計的結果也是以為550 nm主，所以提出了三波長的設計方法，使優化能擴展至藍光與紅光。並且經由與傳統設計的比值，可知道在兩層延遲片時，三波長設計的白、紅與藍光色差只有傳統設計的11%、82.14%與12.53%；在三層延遲片時，三波長的白光與藍光色差只有傳統設計的9.09%與13.4%。BBR has been widely applied for LCD display. However, the previous studies did not include rotatable analyzer and the compensated retarder. When the analyzer rotates, the retardation vs. wavelength relationship is failed to represent both the transmittance vs. wavelength property and the color performance. In this paper, the authors proposed multiple evaluation metrics to measure the image quality. The total luminance ratio, crosstalk and color shift metrics are defined and used to evaluate the image quality. The optimization of broadband retarder shows improvement of 26.17% for white crosstalk, 38.55% for red color shift and 21.1% for green color shift problems. Then, we use the numerical solution to analyze the performance by varying material, number of layer, structure, and retarder’s angle. For one retarder layer, the crosstalk of white light is less than 0.015 and color-shift of white light is less than 0.014 when viewer’s rotation angle is 90°. For two retarder layers, the crosstalk of white light is less than 0.0007 and color-shift of white light is less than 0.001 when viewer’s rotation angle is 90°. For three retarders layers, the crosstalk and color-shift of white light can be reduced to less than 0.00004 when viewer’s rotation angle is 90°. Finally, because the previous study is focused on green light, we propose the three color based design method for improving the performance in red and blue light. Comparing with the previous study, the color-shift of three color based design is better. For two retarders layers, the ratio of color shift by using three color based design with respect to the previous study are 11%、82.14% and 12.53% for white, red and blue light. For three retarders layers, the ratio of color shift by using three color based design with respected to the previous study are 9.09% and 13.4% for white and blue light