臺灣博碩士論文加值系統

本論文提出陣列波導光柵(AWG)所建構的可調控頻譜相位(programmable spectral phase coding)編解、碼器運用於被動式光纖到府(FTTH)網路。為了改善傳統頻譜相位編解碼架構的位元錯誤率(bit error rate)、系統的私密性(Confidentiality)與信號雜訊比(signal-to-noise ratio)等系統效能，本論文中使用者光指配碼將利用Walsh-Hadamard互補碼於頻譜相位編、解碼中且建構一套頻譜相位碼的變換機制。
然而，當竊聽者能夠獨立竊聽單一使用者訊號(例如：上傳網路)，使用者所使用的頻譜相位碼將可能被光混合檢測器(optical beat detector)於數秒內竊取使用者碼型，相較於暴力猜測法(brute force searching strategy)，竊聽者使用此檢測器可達到較有效的攻擊方式。更進一步，為了改善傳統頻譜相位編解碼架構可能遭受竊聽者使用能量檢測器(simple photo-detector)或光混合檢測器竊取使用者資訊，我們將隱藏變換相位碼機制中起始相位狀態(initial phase state)和轉換相位狀態(phase state shifting steps)的資訊，使竊聽者缺乏變換相位狀態資訊下，無法順利竊取使用者碼型以提昇系統安全性。
本論文中，我們將計算竊聽者有效竊取的信號雜訊比(eavesdropper’s effective SNR)和推估竊聽者利用光混合檢測器竊取使用者碼型所需要的時間，且定義私密度的指標(degree of confidentiality, DOC)來進行私密性的定量分析。相較於傳統頻譜相位編解碼架構，結果顯示出本架構可達到較低的位元錯誤率和在竊聽者使用能量檢測器或光混合檢測器攻擊之下提供較佳的私密性。

A new programmable AWG-Based spectral phase coding OCDMA scheme with changing phase state mechanism is configured over a fiber-to-the-home (FTTH) network. In order to improve bit error rate as well as the confidentiality and signal-to-noise ratio (SNR) of conventional spectral phase coding (SPC) OCDMA scheme, the proposed scheme employ complementary SPC code with Hadamard code as signature address codeword and exploit changing codeword mechanism.
Nevertheless, when the eavesdroppers isolate a single user signal (i.e., upstream traffic), the phase chips (i.e., each with a value 0 or p) of user codeword would be extracted within seconds by adopting optical beat detectors, which could be more efficient attack than using brute force searching strategy, and the conventional SPC scheme is vulnerable to such eavesdropping. To further overcome conventional SPC for confidential weakness, the proposed programming complementary SPC scheme is configured to protect against even eavesdropper using either simple photo-detector or optical beat detector to detect ONU codeword. The proposed scheme achieve confidentiality because that eavesdroppers is lacked the changing codeword mechanism based on the initial phase state and shift step knowledge.
In this thesis, the quantitative analyses of network confidentiality are performed by the eavesdropper’s effective signal-to-noise ratio (SNR), the required searching time and the degree of confidentiality afforded against an eavesdropping attack executed using optical beat detectors. Compared to conventional SPC OCDMA scheme, the proposed scheme not only achieves better BER as well as confidentiality under eavesdropper attacking by using optical beat detector.

Chapter 1. Introduction 1
1.1 The Development of EPON Technology over FTTH 2
1.2 The Possible Multiplexing of EPON Technology 4
1.2.1 Time Division Multiplexing over EPON 4
1.2.2 Wavelength Division Multiplexing over EPON 6
1.2.3 Code Division Multiplexing over EPON 8
1.3 Confidentiality of Optical CDMA 9
1.3.1 Increase the Code Complexity 11
1.3.2 Decrease the Eavesdropper’s Signal-to-noise Ratio 12
1.3.3 Change Codewords Frequently 12
1.4 The Motivation of Our Research 12
1.5 Thesis Preview 13
Chapter 2. Overviews on Optical CDMA Techniques 15
2.1 Optical Components in OCDMA System 15
2.1.1 Arrayed-Waveguide-Grating 15
2.1.2 Mode-Locked Laser 17
2.1.3 Liquid-Crystal Spatial Light Modulator 19
2.2 Review the Conventional SPC OCDMA Scheme 21
Chapter 3. The Complementary SPC Codes 24
3.1 The Design of Complementary SPC Codes 25
3.1.1 Walsh–Hadamard based Complementary SPC Codes 25
3.1.2 Programmable Complementary SPC Codes 26
3.1.3 Changing Phase State Mechanism 28
3.2 Realization of the Proposed SPC Encoder 30
3.3 Realization of the Proposed SPC Decoder 34
Chapter 4. Confidentiality Performance of the Proposed System 39
4.1 Correlation and Bit Error Rate (BER) Evaluation 39
4.2 Evaluation of Eavesdropper’s Effective Signal-to-noise Ratio 48
4.3 Evaluation of Required Searching Time for Optical Beat Detector Eavesdroppers 52
4.4 Degree of Confidentiality of the Proposed System 54
Chapter 5. Conclusions 57
Reference 58

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