電控調焦液晶透鏡及應用

Abstract

電控調焦液晶透鏡雖然早在1979年被提出，但由於反應速度慢、焦距變化小與驅動電壓高的問題，阻礙了液晶透鏡在應用上的發展。在這篇論文中，我們首先研究液晶透鏡的光學與物理機制並接著討論液晶透鏡的設計準則。在一般使用液晶透鏡的光學系統中，液晶透鏡僅做為正透鏡操作，因此需要大的液晶層厚度才能得到足夠大的調焦範圍，但液晶層厚度增加會造成液晶透鏡的反應速度變慢(~30 秒)且造成強烈光散射，為了得到反應速度快(<1 秒)且調焦範圍廣(350 cm to 10 cm)的成像系統,我們在成像系統中切換液晶透鏡為正透鏡與負透鏡來調焦，此外，一般圓孔電極的液晶透鏡驅動電壓較高並且難以在均勻的液晶層厚度中實現大部分光學系統所需要的短焦距液晶透鏡，為了得到低電壓與短焦距的液晶透鏡，我們設計了一種使用內建高分子薄膜的液晶透鏡，藉由控制高分子薄膜的折射率分佈與介電常數分佈，我們使高分子薄膜不僅可以作為一個具有固定焦距的內建透鏡外，還可用來調控液晶層的電壓分佈並同時具有配向液晶分子的功能，因此，液晶透鏡的焦距能夠被縮短。除了影像系統外，我們也在論文中使用一般的液晶透鏡與內建高分子薄膜的液晶透鏡，以實現可電控調焦的微型投影機。最後，我們也使用液晶透鏡來實現可光學變焦的全像投影系統，利用液晶透鏡我們可以解決全像投影系統不同顏色影像分離的現象。在論文中，我們解決了液晶透鏡如反應速度、焦距範圍與驅動電壓等主要的難題，同時我們也實現多種不同使用液晶透鏡的應用，我們期望藉由這本論文能為傳統使用幾何光學的光學設計者開啟新的一扇窗並拓展液晶透鏡的應用領域，如內視鏡、光學防手震系統、夜視系統、太陽能與眼鏡等。

Electrically tunable focusing liquid crystal lenses were first proposed in 1979. However, the slow response time, small tunable focal range and high driving voltage of the LC lens impede applications. In this dissertation, we started from a study of optics and physics of the LC lens and discussed the design guideline of the LC lens. In the conventional operation of a positive LC lens only in the imaging system, the large tunable focal range of the LC lens requires the large thickness of the LC layer (or cell gap), but in this way the response time is slow (~30 sec) and the light scattering is strong. To obtain fast response time(<1 sec) and large tunable range (350 cm to 10 cm), we demonstrated a image system using two mode switching which is based on the phase change between the positive and the negative LC lens. Moreover, in order to reduce the driving voltage of the conventional LC lens with hole-patterned electrode and obtain a LC lens with a short focal length which is required in most of image system and is also difficult to realize with a homogeneous cell gap, we designed a LC lens with low driving voltage and short focal length by adopting the built-in polymeric layer. By controlling the spatial distribution of the refractive indices and the spatial distribution of the dielectric constants of the built-in polymeric layer, the polymeric layer can not only be a built-in lens with fixed focal length but also adjust the voltage distribution across the LC layer and align LC directors. As a result, the focal length of the LC lens could be shifted to be short; meanwhile, the driving voltage can be reduced by the polymeric layer. Besides the image system, we also demonstrated the electrically tunable focusing pico projectors with the conventional LC lens and the LC lens adopting the polymeric layer. Ultimately, a holographic projector with optical zooming function by using a LC lens is also demonstrated. The LC lens can be used to solve the color breakup in holographic projectors. In this dissertation, we have overcame several main problems of the LC lens, such as response time, tunable range and the driving voltage, and we also demonstrated various applications based on the LC lenses. We believe this dissertation can open a new window in optical designs based on the classic geometrical optics and also inspire new applications in endoscopes, image stabilization systems, night vision systems, solar cells and eyeglasses.