同調傳輸系統在近年來被廣泛研究，而在同調系統下可以使用不同的調變方式和接收方式，有ASK (Amplitude shift keying)、PSK (Phase shift keying)、FSK (Frequency shift keying)調變方式，和Homodyne detection及Heterodyne detection 接收方式。在同調系統下，解調時必須有一個對比光源，稱為LO (Local oscillator)。
　　上一屆陳瑞軒學長開始我們實驗室第一個同調系統研究。學長是使用BPSK (Binary phase shift keying)調變，利用Pilot carrier方式達成Homodyne Detection，且可以節省在傳輸端的LO (Local oscillator)。而我進而使用QPSK (Quadratic phase shift keying)調變器，以及PBS (Polarization beam splitter)使調變光和Pilot carrier以不同的極化方向同時傳輸，再由程式將擷取到的訊號做計算得出BER。
　　最後以類似的實驗架構將調變器改為20Git/s的PSK訊號，傳輸50公里後，由matlab程式計算BER，以探討兩者的不同。

Coherent transmission system has been extensively studied in recent years, and it can use different modulation formats and different detection techniques. The modulation formats are ASK (Amplitude shift keying), PSK (Phase shift keying), and FSK (Frequency shift keying). The detection techniques are Homodyne detection and Heterodyne detection, and they need a laser in the receiver called as the LO (Local oscillator).
In the previous study, the BPSK (Binary phase shift keying) modulation format was investigated, and the pilot carrier method realized the Homodyne Detection. The merit of the pilot carrier is that it do not need the LO in the receiver. In this master thesis, the QPSK (Quadrature phase shift keying) modulation format is investigated using the pilot carrier method, The BER is calculated using the matlab program.
The performance of 20G bit/s, 50 km transmission system using the BPSK and the QPSK is compared to clarify the merits and demerits of the QPSK modulation.

◎致謝.......................................................................................Ⅰ
◎中文摘要..............................................................................Ⅱ
◎Abstract..............................................................................Ⅲ
◎List of Contents................................................................Ⅳ

Chapter 1 Introduction
1.1 The Coherent System...................................................1
1.2 Motivation.........................................................................2
1.3 The Structure of This Thesis.......................................3

Chapter 2 Technologies of the QPSK Coherent System
2.1 Introduction.....................................................................5
2.2 Homodyne Detection
2.2.1 Coherent System........................................................5
2.2.2 Homodyne Detection.................................................7
2.3 Phase Shift Keying Modulation
2.3.1 Binary Phase Shift Keying Modulation....................8
2.3.2 Quadrature Phase Shift Keying Modulation..........9
2.4 90 Degree Hybrid and the Balanced Receiver......11

Chapter 3 Experimental Study of Different Modulation Formats in Coherent System
3.1 Introduction...................................................................16
3.2 Experimental Setup.....................................................16
3.2.1 Transmitter...............................................................19
3.2.2 Transmission Line.................................................21
3.2.3 The Receiver............................................................23
3.3 Results and Discussions..........................................28
3.4 Conclusion...................................................................31

Chapter 4 Summary.............................................................................34

List of Abbreviations......................................................................35

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