近年來，隨著許多不同的應用多媒體迅速增加，人們對於現代網路的傳輸速率有著較高的要求。因此，如何在短時間內傳送大量的資訊成了一大議題。而相較於傳統的同軸電纜，光纖傳輸有著較大的優勢，例如較小的損耗以及較高頻寬。

而四階脈衝振幅調變訊號逐漸在短距離的光纖通訊系統中被重視，然而四階脈衝振幅調變訊號較一般常用的不歸零訊號需付出較大的調變功率，進而產生嚴重的調變器非線性問題，因此在本論文中我們提出使用光的二位元不歸零訊號調變出四階脈衝振幅調變訊號，此方法對於調變器非線性有著高容忍度。

本論文使用平行的電致吸收調變器利用光的二位元實現光數位轉類比轉換器，在我們的實驗中呈現 50 Gbps 和64 Gbps的光上四階脈衝振幅調變訊號。並且與電上數位轉類比的訊號相比較，光上數位轉類比訊號有較好的表現以及對於調變器的操作特性及非線性特性有著較高的容忍度。

In recently years, there are more and more kinds of internet media; as a result, people are asking for high transmission capacity. Therefore, how to reach higher transmission capacity has become to an important issue. Compared with traditional coaxial cable, fiber has significant advantages, such as less loss and higher bandwidth.
4-level pulse amplitude modulation (PAM-4) has been emphasized in short reach fiber communication system. However, PAM-4 signal has larger modulation penalty compared to binary NRZ, and PAM-4 signal suffers from modulation nonlinearity. As a result, my thesis proposes a novel optical DAC to generate PAM-4 signals featuring high tolerance to modulation nonlinearity.
The proposed novel optical DAC uses parallel EAMs to generate optical 4-PAM signals. A proof-of-concept experiment is demonstrated to verify that the scheme is tolerant to modulator nonlinearity and outperforms the conventional scheme, which is based on electrical DAC and a single EAM.

論文審定書 i
致 謝 ii
摘 要 iii
Abstract iv
目 錄 v
圖列表 vi
第一章 緒論 1
1-1 前言 1
1-2 研究動機 2
第二章 光學調變 4
2-1 光學調變器 4
2-1-1 Mach-Zehnder調變器 (MZM) 4
2-1-2 電致吸收調變器 (EAM) 7
第三章 數位調變模式 8
3-1 偏移鍵 (Shift Keying) 8
3-1-1 相位偏移鍵 (Phase Shift Keying, PSK) 8
3-1-2 頻率偏移鍵 (Frequency Shift Keying, FSK) 10
3-1-2 振幅偏移鍵 (Amplitude Shift Keying, ASK) 11
3-2 脈衝振幅調變訊號 (Pulse Amplitude Modulation) 13
3-2-1 何謂脈衝振幅調變 13
3-2-2 四階脈衝振幅調變訊號的非線性影響 14
3-3 調變器非線性問題 17
第四章 實驗架構與結果 21
4-1 實驗架構 21
4-2 實驗結果 26
第五章 結論 40
參考文獻 41

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[6] http://www.ieee802.org/3/bs/
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[8] A. Ghiasi et al., “Investigation of 100GbE Based on PAM-4 and PAM-8,” IEEE 802.3bm Fiber Optic Task Force, Geneva, Switzerland, Sept. (2012).
[9] Y.T. Chan and L.G. Gadbois, “Identification of the modulation type of a signal,” Signal Processing, vol. 16, pp. 149-154, 1989.
[10] W.J. Huang et al, “Optical DAC for Generation of PAM4 Using Parallel Electro-Absorption Modulators” ECOC 2016, Düsseldorf.