臺灣博碩士論文加值系統

最近十幾年光分碼多重存取技術允許多個使用者同時非同步地存取網路系統利用光纖提供的廣大頻寬，因此這個技術非常適合應用於區域網路中。早期的光分碼多重存取技術系統是在時域上將輸入訊號和近似正交碼序列來進行調變，但這樣所需的碼長很長，且使用者的總數受限於系統中的多重擷取干擾。
因此，我們提出了一個架構用光頻譜相位編碼技術來實現光分碼多重存取，架構中包括了液晶空間光調變器用來做相位編碼，馬赫貞德干涉儀，和一組平衡檢測器來檢測光干涉的訊號強度，利用以頻譜相位編碼為主之光分碼多重存取技術，在接收端運用光的干涉效應和碼的正交特性搭配平衡檢測技術來消除其他使用者的多重擷取干擾，而萃取出預期使用者的信號。然而，在實際傳輸過程中傳送端和接收端的相位並不可能一樣，而產生了相位偏移效應，這可能會導致接收錯誤的訊息，有些論文提出了使用光鎖相迴路來解決，但在實際上難以實現，所以在本篇論文我們對提出的架構去討論和模擬相位偏移效應產生的影響。

In recent years, optical code-division multiple-access (OCDMA) systems have been proposed for multiple accesses to utilize the vast bandwidth available in optical fiber. Optical CDMA systems are believed to provide asynchronous access for each user in the system, which is especially suitable for usage in local area network (LAN).
We propose an optical code-division multiple-access (SPE-OCDMA) codecs scheme for proof-of-concept demonstration. The spectrally phase- codecs are constructed with Liquid-Crystal Spatial-Light Modulator (LC-SLM), Mach-Zehnder Interferometer (MZI), and differential balanced photo-detectors. Spectrally phase encoding (SPE) scheme of optical CDMA has been introduced to eliminate the MAI effect by using the orthogonal coding, such as Walsh-Hadamard codes. However, the transmission processes will produce phase shift between transceiver codecs. The phase shift will destroy orthogonality of the signal codes and cause detection error in the receiver. There were articles dealt with solutions using optical phase- locked loop (OPLL), but it’s not easy to implement. We consider the effect of phase shift in the SPC-OCDMA system and good result is obtained with little system degradation.

中文摘要 i
ABSTRACT ii
誌謝 iii
CONTENTS iv
LIST OF FIGURES v
LIST OF TABLES vii
Chapter 1. Introduction 8
1.1 Introduction to Optical CDMA 9
1.2 Optical phase-locked loop 21
1.3 Motivation of the Research 24
1.4 Sections Preview of the Thesis 27
Chapter 2. Overviews on Optical CDMA Techniques 28
2.1 Walsh-Hadamard codes 28
2.2 Liquid Crystal Spatial Light Modulators 31
Chapter 3. System description over Optical Spectral-Phase coding 35
3.1 OCDMA system with the proposed WH codes pairs. 35
3.2 The theory of low coherence interferometer 39
3.3 Receiver detection scheme 42
Chapter 4. The effect of phase shift and system performance 48
4.1 The effect of phase shift 48
4.2 System Performance 55
Chapter 5. Conclusions 61
References 63

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