微型光學元件在提昇顯示元件影像品質的應用

Abstract

隨著多媒體資訊（Multimedia）與網路（Internet）時代的來臨，影像與資訊的交流益形迅速，各種新型顯示影像文字的顯示技術應運而生。而伴隨著這些顯示技術的發展，各種各樣新型光學元件與技術也不斷被提出，來解決各種顯示元件所面臨的問題。其中微光學元件（Microoptical Components）由於具有輕、薄以及平面化等優點，發展十分迅速，亦逐漸被應用在新型的顯示元件上。 平面顯示器（Flat Display）是顯示器的主流，在輕量化、薄型化、與高影像品質等各項要求下，微光學元件是提昇顯示器顯像品質的主要光學技術。本論文利用折射/繞射(refraction/diffraction)光學原理，並發展利用精密加工、半導體微影蝕刻 (lithography /Etching) 與塑膠翻模 (plastic molding) 等微光學的各種製程技術，設計製做出各樣的平面化（planar）微光學元件，來提昇液晶顯示器中的亮度、色彩、對比等影像品質等問題。 由於液晶顯示器使用彩色濾光器（color filter）來產生顏色，使得光的使用效率上僅有約1/3的光效率使用。本論文提出高效率彩色濾光器，利用微型稜鏡結構（micro-prism）與光學干涉式（optical interference）多層鍍膜的彩色濾光鍍膜，可使彩色濾光器的光效率使用提升2倍以上，有效提升液晶顯示器的亮度。 在改善液晶顯示器的顯示品質方面，由於液晶顯示器的彩色濾光器以紅、綠、藍三色子畫素（sub-pixel）構成一完整畫素(pixel)結構，並在三色子畫素間以黑矩陣（black matrix）相隔以達到增加對比(contrast)、保護薄膜電晶體等功能。此黑矩陣造成了液晶顯示器的顯示畫面有明顯的畫素結構，尤其在單片式液晶投影系統中，經投影放大後，此畫素結構會更加明顯，造成影像的不自然寫真與觀賞。為了克服單片式液晶投影系統的明顯畫素結構，本論文設計製作一分光光柵（fan-out grating）元件，將每一子畫素的畫素影像加以複製並有效填補畫素間的黑矩陣空隙，減輕影像的不連續現象，優化單片式液晶投影系統的影像品質。 在直視型反射式液晶顯示器（direct view reflective LCDs）中，為了達到省電的目的，利用液晶顯示器底部的反射面（reflector）來反射環境光，光線在兩次穿透液晶層後經液晶層調變而產生影像。但是對一平面反射面而言，斜向入射的環境光經鏡面反射後亦斜向出射，使得接近使用者觀察方向的正向方向的影像亮度不足，同時由於液晶顯示器表面反射的雜散光，恰與經調變的反射影像光同一方向，亦造成影像對比度不佳。為了改善此缺點，本論文提出離軸設計（off-axis）的非對稱微透鏡陣列(asymmetric microlens array) 此元件可將入射環境光加以偏折至接近正向方向，使得觀賞者觀察角度範圍內的影像亮度增加，同時減低表面反射，可同步增加影像的對比度。如此可大幅改善反射式液晶顯示器的影像品質，並增加其應用的範圍。

As the trend of multimedia, Internet and communication applications, various display technologies to present mass information in image, text, and video, are rapidly developed to fulfill the demands of vast amount of information exchange. To facilitate the development of display technologies, various new optical components and technologies are proposed to resolve the issues in display performance. Among these optical technologies, microoptical components, due to the advantages of light, thin, and planar structure, are being rapidly developed and well applied for novel applications, including enhancement of display image quality. Flat panel display is the major trend for display technologies. In order to meet the requirements of light weight, compact size, low power consumption, and high image quality, microoptical components provide key solutions to fulfill the demands and to improve the quality of display devices. In this thesis, based on the refraction/diffraction optical component design, various fabrication technologies, including precise machining, VLSI lithography/etching, and plastic molding, are used to develop several planar microoptical components to improve image performance of liquid crystal displays in various aspects, such as brightness, color, contrast, and image quality. Because the conventional color filters of LCDs transmit needed spectrum and absorb the undesired spectrum to achieve display colors, the efficiency of this type of color filter is of no more than 33%. In this thesis work, we proposed high efficiency color filters comprised of microprisms and interference color filters to redistribute the total energy of entire spectrum to the respective color subpixels, generating color for viewing. As a result, the efficiency of the color filters has been improved by more than a factor of 2, effectively increased the overall brightness of LCDs. In an active-matrix liquid-crystal display (AMLCDs), each pixel is controlled by a thin film transistor and surrounded by data and gate electrodes, causing an opaque area of "dead space" between pixels. In the LCDs projection system, the "grain-like" pixel structure resulting from the dead space produces an uncomfortable discontinuous sight in viewing. We designed and fabricated a multilevel "fan-out" grating to duplicate the image of each color sub-pixels and then fill the dead space between each pixel. Simultaneously, the spatial frequency of the color subpixel distribution within the total images is increased. Consequently, the grain-like pixel structure in projection images is suppressed, at a small cost of the resolution of image. Reflective LCDs, without a built-in light source, utilizing the ambient light as main source for illumination are of low power consumption. Conventional reflective LCDs with a metallic reflector reflect modulated light for viewing. Under oblique illumination, the specular reflection of planar reflector reflects the oblique incident light to the corresponding reflection angle, so that the viewers can not view the brightest image in the typical viewing region, at normal direction of LCDs. Moreover, the brightest reflected image is at the glare angle where reflection from the front glass, causing the reduction in contrast. To resolve the above deficiencies, we developed an "off-axis microlens array light control film" to enhance both the brightness and contrast of reflective LCDs. The off-axis microlens light control film directs incident light into a reflection cone near normal direction. Therefore, the brightness of image in the typical viewing region of viewers is increased, and contrast ratio of image is also enhanced by suppressing surface reflection. As a result, the image quality of reflective LCDs can be greatly enhanced to achieve the various applications in portable, hand-held devices.