近年來全球資料量將急速攀升，對於資料中心的容量需求也隨之增加，因此低成本、高容載量的光通訊系統被應用在資料中心內部以及資料中心之間傳輸，傳輸距離從數百公尺到數十公里不等。相較於二進制訊號，四階脈衝振幅調變(PAM4)訊號能夠提升一倍的傳輸速率，且具有較好的頻譜效益。
本論文的研究目的主要為增加四階脈衝振幅調變訊號在資料中心的傳輸距離，為此我們提出了兩個方法，其一是在四階脈衝振幅調變系統中加入決策迴授等化器(DFE)，其二使用雙二進制的四階脈衝振幅調變(Duobinary PAM4)作為傳輸訊號格式，達到頻寬減半的效果。我們透過實驗證明四階脈衝振幅調變訊號使用決策迴授等化器之後系統架構的可行性。另外也使用雙二進制的四階脈衝振幅調變系統，在不加入任何補償的情況下，相較於傳統的四階脈衝振幅調變，雙二進制的四階脈衝振幅調變系統有較好的色散容忍力，相對的接收也需要較高的訊號雜訊比(Signal-to-Noise Ratio)，因此本論文也針對傳統的四階脈衝振幅調變及雙二進制的四階脈衝振幅調變系統對於訊號雜訊比的需求進行討論。

As the increase of the growing demand of information, it requires huge data capacity in data centers. Optical network systems with lower cost and higher capacity is used to support intra and inter data center connections. The distance is in the range from hundred meters to kilometers. Relative to binary signal, 4-ary pulse amplitude modulation (PAM4) can double the data rate and offers higher spectral efficiency.
The main purpose of this study is to increase the transmission distance of PAM4 signals in and among data centers. One method is to achieve the distance is applying Decision Feedback Equalizer (DFE) in the receiver of an optical PAM4 system, and the other method is to employ an optical duobinary PAM4 signal format which half-reduces communication bandwidth. We experimentally demonstrate a 50 Gb/s PAM4 system with a 2-tap Decision Feedback Equalizer (DFE) and hard decision. The BER performance are evaluated with different transmission scenarios without and with DFE respectively. A 10-km single mode fiber (SMF) transmission is achieved by using DFE. In addition, we experimentally evaluate the chromatic dispersion tolerance of a duobinary PAM4 signal for data center communication. In comparison of ordinary PAM4, the duobinary PAM4 has higher dispersion tolerance without any physical or digital compensation, but it requires more receiving SNR. We also discuss the SNR requirement of duobinary PAM4 in comparison with ordinary PAM4.

摘要 I
ABSTRACT II
ACKNOWLEDGEMENT III
CONTENTS IV
LIST OF FIGURES VI
Chapter 1 Introduction 1
1.1 Background 1
1.2 Motivation 4
1.3 Thesis Organization 6
Chapter 2 Literature review 7
2.1 Dispersion in Optical Fiber 7
2.2 Decision-Feedback Equalizer (DFE) 13
2.3 Literature review 15
Chapter 3 Operation Principles 21
3.1 Duobinary PAM4 Coding 21
3.1.1 Duobinary 21
3.1.2 Duobinary PAM4 25
3.2 Mach-Zehnder modulator 26
3.3 Eye Diagram Analysis and BER Calculation 32
Chapter 4 Experimental Results 35
4.1 25 Gb/s signals 35
4.1.1 Experimental Setup 35
4.1.2 Experimental Results 39
4.2 50 Gb/s signals 43
4.2.1 Literature review 43
4.2.2 4.2.2 Simulation Results 47
Chapter 5 Conclusions 50
References 51

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