全像光學資訊儲存系統之探討及其在圖像識別之應用

Abstract

本論文係研究全像光學資訊儲存系統及其應用，包含儲存材料與液晶光學空間調制器的特性探討，以及其在光學圖像識別之應用。 在光折變晶體薄片方面，我們分別由理論與實驗上探討了如何由雜質摻雜濃度來控制鈮酸鋰晶體的光折變特性，且提供了一個設計法則，用來針對光資訊處理系統所需的繞射效率與反應時間來設計晶體的特性參數。其次，在實驗上我們利用摻雜濃度為0.59mole%的鈮酸鋰晶體薄片，建立了一個具位移不變特性之聯合轉換相關器，且其辨識速率可達每秒四張圖像。另一方面，利用摻雜濃度為0.15mole%的鈮酸鋰晶體薄片建立一個具位移不變的VanderLugt相關器。 對液晶光學空間調制器而言，我們定義了調制傳輸函數(簡稱MTF)，用來描述此空間調制器在振幅調制模式下之空間頻率響應特性，並以光學實驗量測之。其次，由實驗實際探討了液晶光學空間調制器的顯示特性，此外，並應用此液晶光學空間調制器的顯示特性於聯合轉換相關圖像辨識系統中，以得到較佳的相干辨識輸出結果。 在實際應用上，我們建立一應用相位多工儲存技術的異關聯記憶系統，除了以電腦模擬分析此異相關記憶系統的特性外，並以光學實驗驗證之。此外，我們提出兩種不同的技術--相位匹配濾波器或邊緣強化技術，以減少輸出圖像的串音干擾，進而提升系統的儲存容量，並建立一個光學異相關聯想記憶系統。 最後，探討儲存材料的非均向性形變效應，針對穿透式與反射式兩種不同的儲存架構來作理論推導與分析，探討在此光柵形變效應對這兩種儲存架構的影響，並提出一個設計法則，設計一個最佳化的全像儲存系統，以提高儲存系統的儲存容量。

An investigation on holographic information storage and its applications are presented. For storage materials, we have studied both heavily iron-doped LiNbO3 crystals and photopolymer materials. The effects of the donor acceptor concentration ratio in iron-doped lithium niobate crystal plates on photorefractive responose time and on grating diffraction efficiency are studied both theoretically and experimentally. The results provide a useful guide for designing photorefractive plates for optical information processing applications. Two devices for real-time image recognition have been demonstrated: a photorefractive joint-transform correlator and a VanderLugt correlator. The former emphasizes fast response time, and the latter emphasizes high diffraction efficiency. By appropriate adjustment of the dopant concentration and the ratio of the donor acceptor levels, photorefractive Fe:LiNbO3 crystals that facilitate specific applications have been designed and fabricated. Shift-invariant image correlations have been achieved. In the second part of the dissertation, the modulation transfer function (MTF) of a pixelated liquid crystal spatial light modulator has been derived as a function of the fill factor. Based on the formula, we have investigated the dependence of the MTF on the orientations and spatial frequency of the input patterns. Furthermore, we have proposed and demonstrated a method for improving the MTF of a LC-SLM. On the other hand, we propose to use the directionality of a spatial light modulator to increase the performance of a joint transform correlator. Our experimental results show that input space-bandwidth product of a joint transform correlator can be significantly increased by recording a hologram so that interference fringes run along the horizontal direction of a spatial light modulator. For the applications, a hetero-associative memory using the phase-multiplexing technique to achieve multiple-associative pairs is presented. Two methods for reducing the cross-talk between different association pairs are proposed. An optical experiment for the edge-enhancement associative memory is also demonstrated. Finally, we consider the effect of grating detuning on volume holographic data storage using photopolymer recording material. By using the Bragg matching condition, the angular shift and the decay of the diffraction efficiency of the reconstructed beam for transmission and reflection hologram are obtained. A useful guide for selecting an appropriate incident angle of two writing beams is proposed. The distortion of the readout data page is described, and a method for pre-compensation by deviating the incident angles of the reading beam from the original writing beam is discussed.