光接取技術(Optical fiber access technology)是實現將寬頻通訊給每個用戶的關鍵技術，而目前被動光網路(PON)是可以讓用戶享有高速的網路存取。 隨著寬頻存取的需求日益漸增，發展新的技術的研究去實現寬頻接取系統是相當重要。目前，波分多工(WDM)被動光網路是被當作未來實現寬頻光接取系統的技術。近年來的被動光網路系統從中心網路為起點涵蓋20公里的範圍。因為接取系統的市場是集中在人口密集的區域，為了增加可應用的範圍而要求去延長此網路系統的距離。因為世界上有很多區域的人口是比較不密集，所以本篇論文集中討論如何延長波分多工被動光網路系統的距離。
單一光纖做80公里的雙向對稱上下行10.66Gb/s速度的資料傳輸傳輸之波分多工被動網路系統在本篇被提出。為了延長波分多工被動光網路系統的距離，我們採用萊曼放大器(Raman amplifier)。因為萊曼放大器可同時放大雙向的光信號，將有效率的延長波分多工被動光網路的距離。雖然如此，因為萊曼放大器的引入而造成一些效應使得效能降低，所以分辨清楚這些效應及提供解決方法是相當重要，而這篇論文也討論這類的問題。雷利散射(Rayleigh backscattering)是影響效能的重要因素之一，因為萊曼放大器也會放大雷利散射，所以它會影響到信號而造成串音(Crosstalk)更為嚴重。
首先，我們做實驗去討論雷利散射的影響，並提出方法去克服串音造成的效能降低。而另外一組實驗，實現了80公里具萊曼放大器之波分多工光網路系統，驗證了此系統的可行性。最後，這篇論文以成功的驗證延長距離之波分多工被動光網路系統做為結論。

Optical fiber access technology is the key to realize a broadband communication for everyone, and the passive optical network (PON) is enabling customers to enjoy high-speed internet access now. As the demand for the broadband access is still growing, a study to find out technologies to realize wider bandwidth for the access system is quite important. At this moment, wavelength division multiplexing (WDM) PON is the most promising technology for the future optical fiber access system.
Current PON system covers a reach of within 20km from a central office, because the market of the access system is focusing on well-populated area. It is required to extend the reach of the PON system to enhance the applicable area, because there are many regions in the world where are not so highly populated. Therefore, this master thesis is focusing on to enhance the reach of the WDM-PON system. A little more specifically, a single fiber bidirectional 80 km WDM PON system with symmetric up-and-downstream data rate of 10.66Gb/s is reported. In order to enhance the reach of the WDM-PON system, Raman amplifier is utilized. As the Raman amplifier can amplify both directional optical signals simultaneously, it is quite effective to enhance the reach of the WDM-PON system. Even though, there are several effects that cause performance degradations of the system by introducing the Raman amplifier. It is important to clarify such effects and to provide solutions. This thesis discusses these issues also.
One factor to degrade the system performance is the Rayleigh backscattering. As the Raman amplifier amplifies the Rayleigh backscattering, it interferes to the signal and causes the crosstalk penalty. At first, an experimental study has been conducted to clarify the significance of the Rayleigh backscattering, and the method to overcome the crosstalk penalty is presented. Then, another experiment to realize 80km WDM PON system with Raman amplifier is conducted, and it demonstrates a feasibility of such system. Finally, this thesis is concluded by a successful demonstration of the WDM-PON system with an enhanced reach.

中文摘要.......................................................................................................................I
ABSTRACT.................................................................................................................II
List of abbreviations..................................................................................................III
Chapter 1 Introduction................................................................................................1
1.1 Technological trend of the access network...................................................1
1.2 Motivation of this thesis.................................................................................2
Chapter 2 A proposal of next generation PON system concept...............................4
2.1 Introduction....................................................................................................4
2.2 The concept of current PON system.............................................................4
2.2.1 TDM-PON...........................................................................................4
2.2.2 WDM-PON..........................................................................................5
2.3 Concept of the proposed PON system..........................................................6
Chapter 3 Technical problems existed in the proposed PON system......................9
3.1 Introduction....................................................................................................9
3.2 Effects of coherent and incoherent crosstalks in bidirectional transmission system.............................................................................................9
3.2.1 Effect of Rayleigh backscattering in optical fiber transmission.....9
3.2.2 Principle of Raman amplifier..........................................................10
3.2.3 Coherent crosstalk (homowavelength linear crosstalk).................12
3.2.4 Incoherent crosstalk (heterowavelength linear crosstalk).............12
3.2.5 Calculation of coherent crosstalk and incoherent crosstalk.........12
3.3 Experiment to verify the issue of the proposed PON system...................13
3.3.1 Experimental setup...........................................................................13
3.3.2 Experimental result..........................................................................14
3.4 Strategy to eliminate the effect of coherent and incoherent crosstalk.....16
3.5 Conclusion....................................................................................................18
Chapter 4 Long reach WDM-PON system using Raman amplifier......................19
4.1 Introduction..................................................................................................19
4.2 Experimental setup......................................................................................19
4.3 Results and discussions................................................................................20
4.4 Conclusion....................................................................................................41
Chapter 5 Summary..................................................................................................42

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