近年來，光通訊在遠距離傳輸系統中佔有越來越重要的趨勢。而高重複率短脈衝傳輸光源也變成眾所矚目的主題，尤其分波多工(DWDM)系統中，更不可或缺的焦點。
在比較光纖雷射跟半導體雷射後，可發現光纖雷射的特性比較符合用來當成遠距傳輸系統的光源。光纖雷射有分為主動鎖模參鉺光纖雷射(AML-EDFL)、被動鎖模參鉺光纖雷射(PML-EDFL)以及混和所模參鉺光纖雷射(HML-EDFL)。然而在製作鎖模光纖雷射中，我們除了要求短脈衝、高重複率、高輸出能量、高超模壓縮比例(SMSR)之外更在意的是它的穩定性，比較可知主動鎖模參鉺光纖雷射較容易達成。在近年來的報告中有用許多的方式來達到low jitter的效果。相較於此篇論文更加入了高頻電路或更多穩定機制來達成。而在這篇論文上，我們只使用了三組元件的鎖相迴路(PLL)來達成我們的需求。
在鎖相迴路當中，我們使用雙平衡混和器(DBM)、低頻濾波器(LPF)、以及一壓電材料PZT來達成光纖回授機制。PZT本身纏繞光纖並嵌入在環形共振腔當中，其隨著輸入電壓而改變光纖長度，在輸入電壓零伏到十伏之間長度變量可改變4.5微米，而4.5微米相對於玻璃溫度膨脹係數變量約正負五度。PZT在回授系統中佔有主要的回授頻寬限制。在最後我們得到重複率10GHz、超模壓縮比例48dB、timing jitter改善50%、可穩定45分鐘以上之短脈衝。最後，我們將10GHz的脈衝打入OTDM之後，可以得到穩定20GHz的光源輸出。

Abstract

In recent year, optical communication becomes more and more important, especially in long distance network communication. The optical sources play an important rule in the system.
Fiber optical transmission using a short optical pulse train is a fundamental technology in order to achieve a high-speed and long-distance global network. For ultra-high speed fiber optical communication, the characteristic of ideal transmission source is demanded to be stable (low amplitude jitter), widely tunable wavelength, transform limited, low timing jitter, adjustable pulsewidth, and high extinction ratio. Therefore, a mode-locked erbium-doped fiber lasers (ML-EDFLs) source with high repetition rate and short pulse width is good selection than semiconductor lasers for ultrahigh-speed communication system. Besides, these ML-EDFLs can produce higher output power and lower insertion loss in all fiber system.
In recent paper, they mention some methods to solve the problem of stability of the optical mode-locked fiber laser systems, but it needs some more device or high frequency circuit. In this thesis, we use phase locked loop to make the system stable. And the final result improved by PLL.

[1] E. Snitzer, “Optical maser action of Nd in a barium crown glass”, Physical review letters, 7, 1961, pp.444

[2] J. Stone and C. A. Burrus, Appl. Phys. Lett. 23, 388 (1973).

[3] P. C. Becker, N. A. Olsson, J. R. Simpson, “Erbium-Doped Fiber Amplifiers-Fundamentals and Technology”, ACADEMIC PRESS, 1997, pp. 162-163

[4] W. L. Barnes, S.B. Poole, J. E. Townsend, L. Reekie, D. J. Taylor, and D. N. Payne, “Er-Yb and Er doped fiber lasers”, J. Lightwave Technol. 1989, 7, pp. 1461

[5] J. D. Kafka, T. Baer, and D. W. Hall, “Mode-locked erbium-doped fiber laser with soliton pulse shaping”, Opt. Lett., 1989, 14, pp. 1269

[6] H. Takara, S. Kawanishi, M. Saruwatari, and K. Noguchi, “Generation of highly stable 20 GHz transform-limited optical pulses from actively mode-locked Er3+-doped fibre lasers with an all-polarisation maintaining ring cavity”, Electron. Lett., 1992, 28, pp. 2095

[7] X. Shan, D. Cleland, and A. Ellis, “Stabilising Er fiber soliton laser with pulse phase locking”, Electron. Lerr., 1992, pp.182

[8] T. Peiffer and G.. Veith, “ 20 GHz pulse generation using a widely tunable all-polarisation preserving erbium fibre ring laser”, Electron. Lett. , 1993, pp. 1849

[9] Eiji Yoshida, Naofumi Shimizu, and Masataka Nakazawa, “A 40-GHz 0.9-ps regeneratively mode-locked fiber laser with a tuning range of 1530-1560 nm”, IEEE Photonics Technology Letters, 1999, 11, pp. 1587

[10] M. Nakazawa, “ Solitons for breaking barriers to terabit/second WDM and OTDM transmission in the next millennium”, IEEE J. on selected topics in Quant. Electron., 2000 , pp. 1332

[11] L. F. Mollenauer and R. H. Stolen, “ The soliton laser”, Opt. Lett., 1984, pp.13

[12] K. J. Blow and D. P. Nelson, “ Improved mode locking of an F-center laser with nonlinear nonsoliton external cavity”, Opt. Lett., 1988, pp.1026

[13] V. J. Matsas, T. P. Newson, D. J. Richardson, and D. N. Payne, “Selfstarting passively mode-locked fibre ring soliton laser exploiting nonlinear polarization rotation”, Electron. Lett., 1992, pp.1391

[14] K. Tamura, H. A. Haus, and E. P. Ippen, “ Self-starting additive pulse mode-locked erbium fibre ring laser”, Electron. Lett., 1992, pp.2226

[15] K. Tamura, L. E. Nelson, H. A Haus, and E. P. Ippen, “ Soliton versus nonsoliton operation of fiber ring lasers”, Appl. Phys. Lett., 1994, pp. 149

[16] C. S. Tsai, “Study of an active harmonic mode-locked fiber laser stabilized by a semiconductor optical amplitude”, Institute of Electro-Optical engineering in NCTU, master thesis, 2003

[17] Govind P. Agrawal, “Applications of Nonlinear Fiber Optics”, Academic Press, Chap. 5, 2001.

[18] R.L. Fork, B. I. Greene, and C.V. Shank, “Generation of optical pulse short than 0.1 psec by colliding pulse mode locking”, Appl. Phys. Lett.,1981, pp. 671

[19] H. A. Haus, J. G. Fujimoto, and E. P. Eppen, “Structure for additive pulse mode locking”, J. Opt. Soc. Am. B., 1991, pp. 2068

[20] K. Tamura, E. P. Ippen, H. A. Haus, and L. E. Nelson, “77-fs pulse generation form a stretched-pulse mode-locked all-fiber ring laser”, Opt. Lett., 1993, pp.1080

[21] S. Y. Chen and J. Wang, “Self-starting issues of passive self-focusing mode locking”, Opt. Lett., 1991, pp.1689

[22] Herman A. Haus, “Mode-locking of Lasers”, IEEE J.on Selected topics in Quant.
Electron., 2000, pp. 1173

[23] M. P. Tian, “High repetition rate femtosecond hybrid mode-locked Er-fiber lasers by asynchronous modulation”, Institute of Electro-Optical engineering in NCTU, master thesis, 2003

[24] D. J. Kuizenga, and A. E. Siegman,”FM and AM mode locking of the homogeneous laser-PartΙ:Theory ”, IEEE K. Quant. Electron., 1970, QE-6,(11), pp. 694-708

[25] S.G. Edirishinghe, and A.S. Siddiqui, “Stabilised 10GHz rationally mode-locked erbium fibre laser and its use in a 40Gbit/s RZ data transmission system over 240km of standard fibre” IEE Proc.-Optoelectron., 2000, pp. 401-406

[26] Z. Ahmed, and N. Onodera, “High repetition rate optical pulse generation by frequency multiplication in actively mode-locked fibre ring lasers”, Electron. Lett., 1996, pp. 55-57

[27] R. Kiyan, O. Deparis, O. Pottiez, P. Megret, and M. Blondel, “Long term stable operation of a rational harmonic actively mode locked Er doped fiber laser with repetition rate doubling” Proc. of European Conf. on Optical Communication, ECOC’93, September 1999, Nice, France, pp. 180-181

[28]Best, R. E. (1997). Phase Locked Loops, Design, Simulation, & Applications, 3rd ed., New York: McGraw-Hill

[29]Wolaver, D. H. (1991). Phase-Locked Loop Circuit Design, Englewood Cliffs, NJ: Prentice-Hall.

[30]U. L. Rohde, Digital PLL Frequency Synthesizers, Prentice-Hall: Englewood Cliffs, New York, 1983.

[31]P. K. Maharana and V.K. Agarwal Control System Group ”Phase-Locked Loop Design for Flexible Mode Tracking”, 2003 IEEE.

[32] X. Shan, D. Cleland, and A. Ellis, “Stabilising Er fiber soliton laser with pulse
phase locking”, Electron. Lerr., 1992, pp.182