一種具內建式聚合物薄膜之電控焦距液晶透鏡的光學特性研究

Abstract

我們自行開發出一種具內建式聚合物薄膜之電控焦距液晶透鏡，此液晶透鏡原理是利用聚合物薄膜的介電係數空間分佈來產生不均勻電場，液晶層的液晶指向矢隨電場作軸向轉動，產生透鏡聚焦效果。此液晶透鏡具有低電壓操作的優勢，但對焦範圍過小且其光學特性也尚未仔細研究。在本論文中，我們分析此種液晶透鏡之光學原理與找出對焦範圍過小的成因，並提出方法增加對焦範圍。仔細研究後我們發現對焦範圍過小最主要的限制在於施加均勻電場於液晶透鏡時，透鏡中間與透鏡孔徑邊緣的液晶分子軸向同時轉動造成折射率差值過小。為此，我們另提出利用疏密程度不均的聚合物網絡液晶(PNLC)來增進透鏡中間與透鏡孔徑邊緣的液晶分子軸向的折射率差，並以實驗驗證我們的想法。此論文找出具內建式聚合物薄膜之電控焦距液晶透鏡對焦範圍過小的原因並克服之，此液晶透鏡可能的應用為電控液晶眼鏡、手機成像系統、微型投影機。

We have developed an electric tunable-focusing liquid crystal (LC) lens with a built-in polymeric layer. The operating principle of such a LC lens is that a built-in polymeric layer with a spatially distribution of dielectric permittivity helps generating an inhomogeneous electric field to the LC layer and then the LC directors are reoriented by the electric fields to form the lens-like phase profile. The main advantage of such a LC lens is low driving voltage. However, the tunable focusing range is small and the optical properties have not been studied yet. In this study, we analyzed the optical properties of the LC lens. We discussed the reasons why the focusing range is small, and also proposed solutions to improve it. After analyzing and studying, we found out that the main limitation causing small tunable focusing range is that LC the directors in the center of the aperture and at the edge of the aperture moves simultaneously and then results in small difference of refractive indexes when a homogeneous electric field applies to LC layer. To overcome this, we proposed a gradient polymer network liquid crystal (PNLC) with a special design to increase the difference of refractive index, and proved the idea by the experiments. The potential application of the LC lens with a built-in polymeric layer is electrically tunable focusing eye-wears, imaging systems in portable devices and pico-projection systems.