低液晶濃度之高分子分散型液晶製作及其用於菲涅爾透鏡之可行性

Abstract

本研究提出了一個創新的方法來製作出可調變焦距之透鏡。透鏡之焦距長短可以藉由施加不同的電壓來改變。 在元件的設計中主要討論的重點在於選擇材料和元件的結構這兩大部分。在材料的部分，選擇了高分子分散型液晶(Polymer-dispersed liquid crystal, PDLC)，其最大的特點為液晶具有光學的異向性，不使用一般液晶，而選擇PDLC的原因在於其不依賴光的偏振性，因此元件不需要外加偏振片。在研究中，使用低濃度液晶比例配製PDLC且用高光強度之紫外光曝光，使材料呈現透明狀。在元件結構上，製作成菲涅爾透鏡(Fresnel lens)之形狀取代一般平凸透鏡，菲涅爾透鏡原理是將傳統之透鏡分成數個區域，再將每個區域中的厚度去除掉，僅保留原本表面之曲率，此結構具有質量輕和厚度薄等優點。 元件之運作原理為使用兩平行之導電玻璃基板當作導電層，藉由施加電壓使PDLC材料產生折射率的變化，當元件結構之折射率產生變化，透鏡之焦距也會因此產生改變。最後，藉由不同的元件製作方式，進一步探討利用高分子分散型液晶製作菲涅爾透鏡之可行性。

The study proposes an innovative way to fabricate tunable-focus lenses. The focal length of the lens can be changed by the applied different voltage. The design is divided into two parts. One is the material and the other is the structure of the components. We select polymer dispersed liquid crystal (PDLC) as the material because of optical anisotropy characteristic and independent of light polarization. In this reason, we use PDLC instead of the general liquid crystal. The device has high transmittance because it do not extra need to add polarizers. In the study, we use PDLC with low concentration liquid crystal and high exposure intensity by UV light. In this way, it can make this material has highly transparent. In the device structure, we use Fresnel lens shape to replace the general planar-convex lens. The principle of the Fresnel lens is as follows: The lens is divided into several regions, and then remove the thickness of each region. After that, we only retain the original surface of the curvature. This structure of Fresnel len has the characteristics of light weight and thin thickness. We use two parallel conductive glass substrates and then apply voltage to cause a change of the refractive index in the PDLC material. When the refractive index of the device structure changes, the focal length also changes. Finally, we discuss its possible use for Fresnel lenses by using the PDLC with low LC concentration.