鈮酸鋰晶體全像儲存熱定影技術之研究

Abstract

本論文係以理論分析、電腦模擬與光學實驗來對全像資訊儲存的熱定影技術進行基礎性的研究。我們從Kukhtarev所提出的光折變方程式出發，再加入描述離子移動的方程式，並利用線性近似法，分別建構出在晶體短路架構與晶體開路架構下之全像儲存熱定影的理論模型。其次，透過電腦計算，我們模擬熱定影之動態過程，並尋找影響熱定影效率的各種因素之最佳化條件。在模擬計算當中，我們並將溫度變化的過渡效應考慮進去，使整個理論更具實用性與完整性。本論文中我們探討兩種熱定影過程：一是低溫記錄、高溫補償、低溫顯影，稱為L-H-L過程。一是高溫記錄、低溫顯影，稱為H-L過程。結果發現，L-H-L過程的關鍵因素為補償溫度與時間，針對某一組晶體參數欲得最佳繞射效率，可先選擇補償時間，再找出對應的補償溫度。而對於H-L過程，給定一組晶體參數則有一個最佳記錄溫度存在，因此應先找出最佳記錄溫度，再找出對應的紀錄時間。此外，對於材料參數與記錄時入射光之角度的選取，我們亦從電腦計算中分別得到一個最佳化的條件。最後，我們以光學實驗，對於理論中所預測的各種現象與最佳條件，進行驗證。實驗結果顯示，在趨勢上幾乎都可以與理論所估計的相符合。這也說明了，我們所建構的理論可以做為設計全像儲存熱定影的一個重要依據。

In this thesis, we investigate the thermal fixing techniques of volume holographic storage in LiNbO3 crystals. We have performed theoretical modeling, computer simulations, and optical experiments. First, we incorporate ionic transport equations into the Kukhtarev's equations for photorefractive crystals. Then by using the linear approximation method, we have developed a theoretical model for thermal fixing under both short-circuit condition and open-circuit conditions on crystals. The temperature transition effect during the heating and cooling processes have been taken into account in our theoretical model. We have considered two processes of the thermal fixing: one is recording at low temperature, compensating at high temperature, and then developing at low temperature, so-called the L-H-L process. The other one is recording at high temperature, and then developing at low temperature, so-called the H-L process. Our calculations show that the compensation time and temperature are two key points of thermal fixing. In order to achieve optimal diffraction efficiency for a given material parameters, we could first choose a suitable compensation time and then the corresponding compensation temperature can be obtained. On the other hand, for the H-L process, there exists an optimal recording temperature for a given material parameters. Therefore, we should first find the recording temperature, and then the corresponding recording time can be obtained. Furthermore, we have also studied the effects of material parameters and the recording angles on thermal fixing. During this investigation we have performed optical experiment. The results show a coincidence with the simulation results. Our studies provide a useful guide for designing the thermal fixing procedures of holographic storage.