應用反向對準型液晶波板研製可調式相位延遲元件之研究

Abstract

在本論文中，我們分析並研製可調式相位延遲波板之元件，作為全像資訊儲存系統中改變光波偏振態器件之應用。我們選用反向對準的間列型液晶晶胞當作設計的基礎，希望利用外加電壓改變液晶晶胞之雙折射特性，達到純相位調製的功能，形成可調式相位延遲板。 首先，我們利用液晶物理理論來分析，在不同外加電壓作用下，液晶晶胞內的液晶分子傾角與位置的關係，將此關係加上廣義Jones矩陣法則，可計算在不同外加電壓下液晶晶胞對入射線性偏振光波產生相位調製的特性，以此為基礎設計可調式液晶相位延遲波板。其次，廣義Jones矩陣法則也可以讓我們分析各種操作參數下，液晶相位延遲板之特性，特別是其視角的問題，本文我們也針對此問題探討，找到一個較佳的厚度。 完成理論分析後，我們進行光學實驗，根據理論分析，首先將製作好的液晶晶胞放置在兩個互相垂直的線偏振板之間，並讓入射面之液晶分子長軸與穿透軸夾45度角，測量正向入射之光穿透強度對電壓的變化，並與理論分析之結果比對，可以得到此液晶晶胞的相位調制特性，並以此設計反向對準液晶相位板作為波板元件的操作參數。其次將入射光改成匯聚的型式,以偏極角椎顯微鏡的方式，觀察視角問題，並與理論比對，得到最佳化設計。

In this thesis, we investigate on the design and fabrication of a tunable phase retardator using anti-parallel (AP) liquid crystal plate for the application on holographic data storage. With applying voltage, birefringence characteristic of liquid crystal cell can be controlled so that the polarization state of light can be switched. Thus, the liquid crystal cell can work as a tunable pure phase retardator. At first, we derive theoretically relationship between the tilted angles of the liquid molecules as a function of the position in liquid crystal cell under different external voltage. Secondly, by using extended Jones matrix method, the phase retardation of input linear polarization wave as a function of the external voltage can be calculated. It is fundament concept to design our device. Furthermore, with help extended Jones matrix method, we can investigate the viewing angle characteristics of the liquid crystal device and then optimize the operation parameters of the liquid crystal cell such as thickness, external voltages for operation of the half-wave and full-wave plates. In experiments, we first prepare the AP liquid crystal cell with different thickness and then place the cell within cross polarizes to form a sandwich structure. By varying voltage across AP cell, we measure transmission of normal incident light. We compare experimental results with theoretic analyses, and then obtain the operation parameters of the device. Then, by introducing an extra lens to converge light into the liquid cell, we measure the transmission of the liquid crystal cell and polarizer sandwich to study about the viewing angle characteristics. With comparison with theoretical analyses, the design parameters of the liquid crystal cell can be optimized.