在先前；我們已經對於架構於布拉格光柵的光分碼多工系統進行探討。這篇論文中；我們在相同的架構下，對於系統中多重存取干擾(MAI)，暨由於緊鄰重疊(overlapping)波長所衍生的光拍差干擾(OBI)同時進行消除之探討。最大長度序碼(M-sequence) 和 Walsh codes 將被應用蝕刻於布拉格光柵，使得；接收端中的平衡檢測器能發揮互相消除mutual cancellation)的效應，如此；可確保多重存取干擾(MAI)暨光拍差干擾(OBI)有效且同時性的被抑制與消除。
理論上；光拍差干擾與所採用準正交碼的run length有重要的相關性，在光領域中；若選用的碼型具有相近的波長出現(wavelength present)暨波長關閉(wavelength absent)的特性。亦即；類比於電領域中信號位元的ON、OFF。如此；我們可預期：在接收端採用布拉格光柵製作的濾波器，當進行透射端與反射端的解碼過程後，投注於一對的後級平衡檢測器，會產生互相消除的效應。由模擬結果顯示：在消除光拍差干擾情形下，系統的信號雜訊比(SIR)仍可維持35db以上。
在光拍差干擾抑制上；有少數碼型無法有效顯現互相消除的效應，我們提出：可將該碼型用於補償解碼器，此舉不僅可解決光拍差干擾問題，而且可用來解決此系統架構因不平坦光源所衍生的多重存取干擾問題。其次；我們提出：在使用者數目(user capacity)保持不變情形下，經由波長適當的穿插配置(wavelength interleaving allocation)而造成護衛帶(guard band)的效果。如此；在電領域上所採用的展頻方法，與我們提議的展時方法互相結合，因此對於此通訊系統架構中光拍差干擾的抑制與降低將更加有效可行。

An optical spectral coding technique in fiber-grating-based optical code-division multiple- access (OCDMA) system has been investigated in our previous work. In this thesis, the same architecture is set up to investigate the reduction of multiple access interference (MAI) and optical beat interference (OBI) induced by those adjacent grating chips. FBGs written as M-sequence and Walsh codes is proposed for such MAI and OBI’s cancellation in spectrally balanced photo-detectors.

Theoretically, OBI is dependent upon run length of pseudo-orthogonal codes. The wavelength vector is characterized by nearly the same number of “on” chips (i.e., logic “1” chips) and “off” chips (i.e., logic “0” chips). In the differential decoding scheme, subtraction of reflected and transmitted branches of wavelength chips will result in mutual cancellation. It is seen that differential decoding scheme characterizes a better error performance on eliminating MAI and OBI problem. Furthermore, the stimulant result is shown SIR above 35 dB on reductions of OBI.

Since a few codes are characterized by the worse performance of suppressing OBI, we propose that worse code pattern is pre-written with isolated encoder/decoder for compensation purpose. This not only decreases MAI due to non-flattened incoherent sources and non-ideal FBG coders, and also OBI caused by the multiple adjacent gratings. Therefore, MAI and OBI is decreased simultaneously. Furthermore, we propose that wavelength interleaving allocation method can result in guard band to suppress OBI. Thus, MAI and OBI will be decreased simultaneously due to combining spreading time and spreading frequency method.

Abstract I
Contents IV
List of Figures VI
List of Tables VIII

Chapter 1. Introduction 1

1.1 MAI and OBI Problems 1
1.2 MAI Reduction by Frequency Hopping and Codes Sequences Technique 6
1.3 OBI Reduction by Clipping Tone and Codes Sequence Technique 10

Chapter 2. MAI Reductions with FBG-Based OCDMA Network 15

2-1 The Architecture of FBG-based OCDMA Network 5
2-2 MAI Reduction by Appling M-sequence Codes 20
2-3 MAI Reduction by Appling Walsh codes 23
2-4 MAI Simulation 27

Chapter 3. OBI Suppression in FBG-Based OCDMA Network 31

3-1 The Solution of OBI Reduction 31
3-2 OBI Reduction by Appling M-sequence Code 33
3-3 OBI Reduction by Appling Walsh Code 34
3-4 OBI Simulation 41

Chapter 4. Compensation for simultaneous MAI and OBI Reduction 51

4.1 Compensation Scheme to Suppress MAI and OBI 51
4.2.Modified FBG Decoder for MAI and OBI Reduction 54
4.3 Guard Band Scheme to Suppress MAI and OBI 57

Chapter 5. Conclusions 62

Reference 64

Appendix 68

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