偏振全像繞射特性研究及其在體積全像資訊儲存之應用

Abstract

在體積全像資訊儲存系統中，多工方法被視為增加儲存容量關鍵技術。除了體積全像布拉格條件方法外，偏振多工也被視為另一種可行性，可讓我們利用光的偏振態儲存在對光偏振態敏感的材料上。近幾年，我們發現實驗室開發的PQ／PMMA感光高分子材料具有光致異向性特性，提供材料記錄偏振全像可行性。 本論文利用向量耦合波方程式，分析偏振體積全像與光強度體積全像之記錄光及讀取光波偏振態與繞射光波偏振態的特性。理論與實驗結果得知：在小角度下近似下，記錄正交圓偏振全像時，讀取光偏振態與原參考光偏振態相同（左旋圓）時，繞射光偏振態為右旋圓偏振態；讀取光偏振態與原參考光偏振態相互正交（右旋圓）時，無繞射光產生。記錄正交線偏振全像下，讀取光偏振態為垂直（平行）線偏振態，則繞射光偏振態為平行（垂直）線偏振態。記錄光強度全像時，繞射光偏振態與讀取光偏振態相同。 最後，由於正交圓偏振態記錄的偏振全像M#和材料敏感S（M#：1.818；S：0.18cm2/J）與光強度全像（Intensity hologram）的特性較接近（M#：2~3；S：~0.5cm2/J），所以我們利用圓偏振設計混合偏振多工與位移多工體積全像儲存系統，同時，利用波恩近似法推導說明位移選擇性，發展更高密度的體積全像資訊儲存系統。

Among the key techniques for holographic memory, the multiplexing schemes are the most important ones, because they allow us to efficiently make use of the huge capacity potential of volume storage. Beside the Bragg condition in a volume hologram, polarization multiplexing is another possibility, which makes use of the polarization state light waves in a polarization-sensitive medium. In recent years, we found that the photo-induced anisotropic in PQ／PMMA can provide the possibility for recording polarization hologram. In these thesis, we use vectorial coupled mode theory to analyze the holographic reconstruction on the polarization states of writing and reading beams. Theory and experimental results shows in the small angle approximation, for the orthogonal circular polarization state polarization holograms, if the polarization state of reading beam the same as the reference beam, the polarization state of diffracted beam the same as the signal beam. If the polarization state of reading beam is orthogonally polarized with respect to the reference beam, there will be no diffraction. For the orthogonal linear polarization holograms, if the polarization state of reading beam the same as the reference beam, the diffracted beam the same as the signal beam. If the polarization state of reading beam is rotated by 90°, the polarization of the diffracted beam will follow the rotation by 90°. For the intensity holograms, the polarization state of diffracted beam is the same as the reading beam. Finally, because the circularly polarized type possesses better dynamic range (M#=1.818) and material sensitivity (S=0.18cm2/J), and the performance is comparable to that of the intensity hologram. Thus we use circular polarization to design a data storage system, in which polarization multiplexing is introduced into a shift multiplexing scheme. Besides, we use Born Approximation to derive the shift-multiplexing spacing, developing the higher storage capacity of system.