臺灣博碩士論文加值系統

本論文係以數值模擬的方式探討直接調變式半導體雷射遭外部光注入後之非線性失真特性。對於模擬計算，雷射系統的特性與動態是以單模方程式來表現。本論文探討此雷射系統在不同的操作和本質參數下，對於諧波和互調失真的影響，以探究適用於實際光纖通訊應用的操作條件。
經由光鎖注入的方式，非線性失真在穩定的光鎖注入條件下可以明顯的減少。在穩定的光鎖注入範圍中，非線性失真減少的現象於不同光注入強度和微調頻率下大部分都能觀察到，由此證明光鎖注入技術是減少非線性失真非常有效的方法。使用光鎖注入之雷射系統其非線性失真減少可達25 dB。在大範圍的調變必v下，非線性失真亦能有效地減少。因為不同雷射系統擁有不同的鬆弛震盪頻率，非線性失真的減少隨著調變頻率變化的情形會有明顯的不同。非線性失真減少通常隨著偏壓電流的增加而減少。本研究也證明非線性失真減少在廣泛的操作和本質參數範圍中都能達到，顯示光鎖注入技術的適用性。
在本研究中，非線性失真減少有兩種主要的機制:經由研究證實增強的鬆弛震盪頻率以及削減的鬆弛震盪共振是造成光鎖注入雷射在高調變頻率下非線性失真減少的主要機制；另一方面，經由研究證實輸出光必v-注入電流 (L-I) 特性的改善是造成光鎖注入雷射在低調變頻率下非線性失真減少的主要機制。

A numerical study on nonlinear distortion in a directly modulated semiconductor laser subject to external optical injection is presented in this thesis. For numerical calculation, a single-mode rate equation characterizing the dynamics and characteristics of the laser system is applied. In this study, harmonic distortion and intermodulation distortion of the laser system as a function of operational parameters and intrinsic parameters are investigated and discussed to explore the appropriate operating conditions for practical applications in optical fiber communications.
Through the injection-locking method, significant nonlinear distortion reduction can be achieved under stable injection-locking. The reduction in nonlinear distortion as a function of injection strength and detuning frequency is observed for most of the region of stable injection-locking, suggesting that the injection-locking technique is a very effective method for nonlinear distortion reduction. Compared to the free-running laser system, significant reduction up to 25 dB in nonlinear distortion is observed. An effective decrease in nonlinear distortion is found over a large range of modulation power. Because of different resonance frequencies for different laser systems, the reduction in nonlinear distortion varies dramatically with modulation frequency. The reduction in nonlinear distortion generally decreases with increasing bias current level. This study shows that the reduction in nonlinear distortion can be obtained over a wide range of operational and intrinsic parameters, indicating the robustness of optical injection-locking technique. The systematic study therefore provides a much greater insight into how the laser should operate for reduction in nonlinear distortion.
Two mechanisms resulting in the reduction of nonlinear distortion are also investigated. One is the enhancement of relaxation oscillation frequency and increase of damping in relaxation oscillation, which significantly reduces nonlinear distortion at high frequencies. The other is the improvement in the linearity of light-current (L-I) characteristic, which is the dominate mechanism at low frequencies for reduction in nonlinear distortion.

Publications and Presentations I
Abstract (in Chinese) II
Abstract (in English) IV
Acknowledgments VI
Figure Caption VII
Contents XIII
Chapter 1. Introduction 1
1.1 Background 1
1.2 Motivation 4
1.3 Organization of Thesis 6
Chapter 2. Laser System 8
2.1 Semiconductor Lasers 8
2.2 Injection Locking Technique 9
2.3 Theoretical Model 9
2.4 Simulation Model 11
Chapter 3. Harmonic Distortion 14
3.1 Introduction 14
3.1.1 Communication System 14
3.1.2 Modulation Response 16
3.2 Effects of Operational Parameters 17
3.2.1 Modulation Frequency 17
3.2.2 Modulation Power 26
3.2.3 Bias Current 31
3.2.4 Injection Strength and Detuning Frequency 32
3.3 Effects of Intrinsic Parameters 33
3.4 Conclusions 39
Chapter 4. Intermodulation Distortion 41
4.1 Introduction 41
4.1.1 Communication System 41
4.1.2 Modulation Response 43
4.2 Effects of Operational Parameters 44
4.2.1 Modulation Frequency 44
4.2.2 Modulation Power 47
4.2.3 Bias Current 52
4.2.4 Injection Parameter and Detuning Frequency 53
4.3 Effects of Intrinsic Parameters 54
4.4 Effects of Frequency Spacing 60
4.5 Conclusions 60
Chapter 5. Conclusion 63
5.1 Summary 63
5.2 Suggestions for Future Work 64
References 66
Figures 76

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