臺灣博碩士論文加值系統

在這個研究中，我藉由兩個極化控制器以及一個偏振相依的光隔離器當作非線性極化旋轉的機制來產生脈衝，在全正常色散的環型共振腔摻鐿光纖雷射中研究短脈衝產生的動態特性。實驗使用中心波長位於974奈米的二極體雷射做為泵激光源，並且使用30公分的單模摻鐿光纖作為增益介質。藉由適當的調整極化控制器，可以得到許多不同的操作狀態，包括Q開關鎖模、群集脈衝鎖模、多波長脈衝鎖模以及一些特殊的調製狀態。在雷射操作在Q開關鎖模狀態時，當泵激功率達292.6 毫瓦，所產生Q開關波包的寬度約為1.4 毫秒，重複頻率則可達到88.9仟赫茲，最大的脈衝能量可達377 奈焦耳。此外，由於Q開關鎖模所產生的高能量光脈衝經過單模光纖所產生的非線性效應，在某些狀況下會使得光頻譜展寬，其波長會由1024 奈米延展到1094 奈米，利用自相關儀量測單一脈衝的寬度大約為71.75 皮秒。另外，當雷射操作在群集脈衝鎖模時，所產生脈衝群集的寬度約1.4毫秒，此寬度隨泵激功率的增加沒有顯著的變化，其重複頻率為4.39仟赫茲，脈衝能量達4.6 微焦耳。另外，藉由適當的調整極化控制器，可以使短脈衝雷射操作在多脈衝的鎖模狀態，從光譜上可以觀察到有9根光頻譜同時存在，每一根光譜的線寬約0.34 奈米，任意兩根光譜的間距約0.68 奈米，所產生脈衝波包的重複頻率約為1.44仟赫茲，其中多波長的產生原因是由於極化控制器擠壓光纖產生雙折射率所造成的光濾波效應，沿不同極化方向的光脈衝遭遇的相位移不同，造成光的干涉效應進而產生光濾波效果。

In this report, we investigate dynamics of mode-locked pulses in Yb-doped fiber laser (YDFL) by the nonlinear polarization evolution (NPE) mechanism in which two polarization controllers and the polarization dependent optical isolator are used inside ring cavity. A diode laser emitting with central wavelength at 974 nm is used as the pumping source and the gain medium is 30 cm single mode Yb-doped fiber. As we proper adjust of the polarization controller, the laser can be operated at different states like Q-switched mode-locking, Bunched mode-lockeing, multi-wavelength laser emission and some peculiar modulated states. When laser operate Q-switched mode-locked state, the repetition rate of Q-switched envelope is 88.91 kHz at, and maximum pulse energy is 377 nJ at 292.6 mW pumping power. At certain polarization state, the measured spectrum of QML pulses become broadening that extends from 1024 nm to 1094 nm due to increase of nonlinear effects as high energy pulse propagation in single mode fiber. The laser reveals broad-band spectrum bandwidth. By means of autocorrelation measurement, the measured pulse duration is about 71.75 ps. In the Bunched mode-locking state, the repetition rate of bunched mode-locked pulse is 4.39 kHz and the maximum pulse energy is 4.62 ?J at 292.6 mW pumping power. At certain polarization orientation, the short pulse with multi-wavelength laser emission can be achieved. About 9 emission peaks coexist and the repetition rate of the pulse bunch is 1.44 kHz. The linewidth of emission peak is about 0.34 nm and the interval of emission peak is 0.68 nm. The reason of the multi-wavelength emission generation is believed to be filtering effect as light propagation in birefringence fiber caused by fiber squeezing from the polarization controllers (PCs). Owing to fiber birefringence, the light with different polarization will encounter different phase shift and will cause interference effect to be a light filter.

Chinese abstract i
English abstract ii
Content v
List of tables vi
List of figures vii
Chapter 1 Introduction 1
1.1 Mode-locked fiber laser 1
1.1.1 Type of mode-locked fiber laser 1
1.1.2 Method of mode-locked fiber laser 2
1.1.3 Yb-doped fiber laser 5
1.1.3-1 Dispersion compensation and ultra-short pulse generation 5
1.1.3-2 All normal dispersion Yb-doped fiber laser 6
1.2 Supercontinuum generation 8
1.3 Q-switched mode-locked and cavity dumping 10
1.4 Motivation 12
Chapter 2 Theoretical background 13
2.1 Dispersion in single mode fiber 13
2.1.1 Material dispersion 13
2.1.2 Waveguide dispersion 15
2.1.3 Chromatic dispersion or total dispersion 15
2.1.4 Profile and polarization dispersion effects 16
2.2 Birefringence 17
2.3 Four-wave mixing 19
2.4 Stimulated Raman scattering 20
2.5 Self-phase modulation and cross-phase modulation 21
2.6 Nonlinear polarization evolution (NPE) 23
Chapter 3 Experimental setup 26
Chapter 4 Results and discussion 29
4.1 CW mode-locked state and Q-switched mode-locked state 29
4.1.1 CW mode-locked state 29
4.1.2 Q-switched mode-locked state 31
4.2 Bunched mode-locked state 37
4.3 Multi-wavelength mode-locked state 41
4.4 Amplifier with the Yb-doped fiber 43
Chapter 5 Conclusion 47
References 48

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