隨著辦公室與家用、以及行動裝置對於網路頻寬的需求持續不斷地增加，而驅使著高速光通訊系統的發展。在最近幾年當中，DQPSK是最吸引人且先進的調變技術之一，這種對光波調變的格式大大地增加了光纖通信系統中的傳輸容量與使用效率。

　　與DPSK比較起來，DQPSK可以一次傳輸兩個位元，也就是說它具有兩倍的光譜效率，這就是DQPSK的主要優點。除此之外，DQPSK具有優異的特性來對抗色散、偏極色散、光塞取多工濾波器與光學干擾。這都使得DQPSK在下個世代的光傳輸系統中扮演重要的角色。

　　分波多工（WDM）的技術是用來將不同波長的雷射同時載入訊號中，在單一光纖裡面作傳輸。這篇碩士論文正專注於利用WDM系統來探討DQPSK在長距離傳輸下的現象。

　　在實驗過程中，DQPSK需要一個特別的技巧來架設。當延遲解調器被用於處理DQPSK的訊號時，透過解碼來使得一連串的接收資料會與一連串的傳輸訊號一致，這樣我們才能正確地在儀器上使用。但是電訊號的編碼或解碼是難以去瞭解的，故我們使用電腦程式來預先計算解碼後的位元，然後把計算好的位元組輸入到錯誤分析儀（ED）當中來量測其誤碼率（BER）。最後，再加以觀察WDM系統中不同通道（波長）的傳輸現象。

　　The ever-increasing requirement for more bandwidth to the office, home, and mobile devices is driving the deployment of high-speed optical communication systems. Differential quadrature phase-shift keying (DQPSK) is one of the most attractive and advanced modulation format in recent years, and this format increases the capacity and efficiency in optical fiber communication systems.

　　DQPSK is able to transmit two bits per symbol. That is to say that DQPSK has twice spectral efficiency compared to DPSK. In addition, DQPSK has excellent tolerance against chromatic dispersion (CD), polarization-mode dispersion (PMD), optical add-drop multiplexing (OADM) filtering, and optical noise. It makes DQPSK play an important role for next-generation optical transmission systems.

　　The wavelength-division multiplexing system (WDM) multiplexes multiple optical carriers in the single optical fiber by using the different wavelengths of laser to carry the signal. This master thesis focuses on the study of DQPSK performance in the long-haul transmission with the WDM system.

　　In the process of experiment, a special technique for DQPSK to be set up is required. When a delay demodulator is applied for the DQPSK signal, decoding is required to make the received serial data become the same as the transmitted serial sequence. As the electronic encoder or decoder is hard to realize, a program is prepared for the experiment to calculate the pre-decoded pattern sequence. Then, calculated patterns are imported to the error detector (ED) to measure the bit error rate (BER). Finally, different channels (wavelengths) of WDM transmission were observed.

致謝　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　I
中文摘要　　　　　　　　　　　　　　　　　　　　　　　　　　　　　III
Abstract　　　　　　　　　　　　　　　　　　　　　　　　　　　　　IV
Contents　　　　　　　　　　　　　　　　　　　　　　　　　　　　　V

1　Introduction　　　　　　　　　　　　　　　　　　　　　　　　　　　1
　　1.1　Background of Long-haul Optical Fiber Communication . . . . . . . . . 1
　　1.2　Motivation of this Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
　　1.3　Structure of this Thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
　　References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2　Theoretical Study of DQPSK　　　　　　　　　　　　　　　　　　　6
　　2.1　Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
　　2.2　Theory of the PSK/DPSK Modulation Format . . . . . . . . . . . . . . . . . 6
　　　　2.2.1　PSK Modulation Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
　　　　2.2.2　DPSK Modulation Format . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
　　2.3　Theory of the QPSK/DQPSK Modulation Format . . . . . . . . . . . . . . 9
　　　　2.3.1　QPSK Modulation Format . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
　　　　2.3.2　DQPSK Modulation Format . . . . . . . . . . . . . . . . . . . . . . . . . 12
　　2.4　The Calculation of the DQPSK Pattern . . . . . . . . . . . . . . . . . . . . . . . 14
　　References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3　Experimental Study of DQPSK　　　　　　　　　　　　　　　　　　19
　　3.1　Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
　　3.2　Experimental Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
　　　　3.2.1　Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
　　　　3.2.2　Transmission Line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
　　　　3.2.3　Receiver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
　　3.3　Experimental Results and Discussions . . . . . . . . . . . . . . . . . . . . . . . 28
　　　　3.3.1　Q-factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
　　　　3.3.2　Single Channel Performance . . . . . . . . . . . . . . . . . . . . . . . . . 30
　　　　3.3.3　WDM Back-to-Back Transmission . . . . . . . . . . . . . . . . . . . . 32
　　　　3.3.4　WDM Transmission through 497 km . . . . . . . . . . . . . . . . . . 34
　　3.4　Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
　　References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4　Conclusion　　　　　　　　　　　　　　　　　　　　　　　　　　41

Acronyms　　　　　　　　　　　　　　　　　　　　　　　　　　　　VII

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