臺灣博碩士論文加值系統

自相位元調變及交叉相位調變為光纖通信系統中主要之非線性效應損害。在非線性光通道中，光反射係數會受到光信號功率影響而有所改變，此柯爾效應觸發自相位元調變及交叉相位調變，擴展光信號之頻譜，進而影響整體通信系統效能。
在本論文中，利用光相位共軛之原理，我們提出了一種光纖非線性效應之補償機制，以減少光信號在傳輸過程中之相位失真。在光纖的中段，一個光相位調變器用來調變輸入光信號之相位。此相位調變的大小正比於輸入光信號之功率，且其正負號與自相位元調變引入之相位偏移相反。因此，在第一段光纖，由光信號功率波動及自相位元調變引入之相位雜訊可以被第二段光纖之非線性相位失真補償。
在系統模擬方面，利用數值分析最佳化光相位調變器之參數。一個利用開關鍵移調變，搭配非歸零碼之光通訊數位系統，在有色散補償之光纖通道下，藉由本文提出之非線性效應之補償方式，在入射光功率及傳輸距離皆可有明顯的改善。

Self-phase modulation (SPM) and cross-phase modulation (SPM) are leading nonlinear transmission penalty in optical communication systems. In nonlinear optical media, an interesting phenomenon of the intensity dependence of the refractive index occurs through SPM or XPM, which leads to spectral broadening of optical pulses and therefor degrade system performance.
A novel scheme for fiber nonlinearity compensation based on the principles of optical phase conjugation (OPC) is proposed to reduce the phase distortion in optical communications. A phase modulator is used to modulate the phase of the data pulses in the middle of fiber spans. The magnitude of the phase modulation is proportional to the detected pulse intensity, and the sign is opposite to that of the nonlinear phase shift caused by self-phase modulation. Thus, the nonlinear phase noise induced by amplitude fluctuation and SPM in the first-half fiber is partially compensated for in the second-half fiber.
Using an optimum value of the phase deviation of the optical phase modulator, we show by numerical simulations that a non-return-to-zero (NRZ) format transmission for 720 km in dispersion-managed system at 40 Gb/s with such nonlinearities compensation can provide greater than 2 dB increase in launch power .

ABSTRACT IV
CONTENTS V
LIST OF FIGURES VII
LIST OF TABLES IX
Chapter 1. Introduction 1
1.1. Optical Nonlinearities Classifications 2
1.2. Nonlinearities in Optical Fibers 3
1.3. Impact of Nonlinear Effects on Optical Communications 5
1.4. Compensation of Fiber Nonlinearities 8
Chapter 2. Theoretical Analysis of Nonlinear Refraction Effects 10
2.1. Principle of Self-Phase Modulation 14
2.2. Effects of SPM on Optical Pulse Propagation 18
2.3. Principle of Cross-Phase Modulation 22
2.4. Effects of XPM on Optical Pulse Propagation 25
Chapter 3. Proposed Nonlinearity Compensating Schemes 29
3.1. Principle of Nonlinearity Compensating Operation 29
3.2. Fiber Nonlinearity Compensation of SPM 32
3.3. Fiber Nonlinearity Compensation of XPM 35
Chapter 4. Simulation Results on the Compensated Systems 39
4.1. Optimization for Nonlinear Coefficient 42
4.2. Performance against Launch Power 44
4.3. Improvement in Transmission Distance 45
Chapter 5. Conclusions 46
References 47

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