多工儲存下的振幅式與相位式圖片之比較

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/7000

Title:	多工儲存下的振幅式與相位式圖片之比較
Authors:	吳銘展;Ming-chan Wu
Contributors:	光電科學研究所
Keywords:	多工儲存;全像術;光折變晶體
Date:	2007-07-10
Issue Date:	2009-09-22 10:34:26 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本論文主要是比較分別以相位式圖片和振幅式圖片作為角度多工儲存資料時，兩者之間的優缺點。我們認為利用相位式圖片來做多工儲存可以有兩個好處: 一個是繞射效率的提升，另一個是誤碼率的降低。在第四章中，我們分別利用相位式圖片和振幅式圖片來作儲存並且比較它們兩者的繞射效率。與振幅式圖片比較，用相位式圖片來做儲存會有較高的光利用效率。因為用相位式圖片來做儲存，記錄於晶體內的光柵數量比較多，所以繞射光會比較強。最後，我們用實驗證實了用相位式圖片來作儲存確實會有較高的繞射效率。現今，大部份儲存的訊號都是以數位方式儲存，在做完多筆資料的儲存後，重建出來的資料可能會跟原始資料不一樣，原因是多工儲存牽涉到抹除問題，因此，重建出來的資料多多少少都會與原始資料有所不一樣。在此，我們想要研究的就是怎麼樣才能降低這個不一樣的程度。在第三章中，我們首先從理論來分析振幅式與相位式被抹除的情形，分析後我們認為用相位式圖片做多工儲存應該會降低這不一樣的程度，在本論文中我們以實驗來查看我們的想法。從第四章的實驗結果看來，我們大概可以說重建出來的相位式圖片之傅氏轉換影像與原始的影像比較接近。但是實驗結果並不是很完美，所以我們目前還沒法給出很確切的結論。In this thesis we have shown the virtues and the drawbacks of phase objects and amplitude objects in holographic storage in LiNbO3 crystal with angular multiplexing . We think that there are two virtues in the use of phase objects: one is the increase of diffraction efficiency, the other is the decrease of bit error rate. In Chapter 4, we have demonstrated experimentally that the recording of a phase object yields higher diffraction efficiency compared with that yields by the recording of an amplitude object. It is thought that this result is due to more gratings are built in the crystal when a phase object is recorded because the object light from a phase object covers the whole crystal. For a practical holographic storage system, usually many pages of information are stored in the crystal. These pages of information are stored in the crystal in series using multiplexing technique. As a result, the information stored in the later portion of the recording sequence will erase the preceding stored information. Accordingly, when the stored information are amplitude objects, the erasing effect will not be uniform over the whole page because the intensity of the stored object is not uniform. Therefore, when the stored data are binary, error bits of information may suffer large change in intensity and become an error bit after thresholding. In Chapter 3, we aim to discuss this problem and supply some experimental results to support this point of view. However, the experimental results are not conclusive and further investigation are needed.
Appears in Collections:	[Graduate Institute of Optics and Photonics] Electronic Thesis & Dissertation

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