直調弱共振腔法布里-珀羅雷射二極體建構10 GHz自回授鎖模光纖雷射之特性研究

Investigation on 10 GHz Self-Feedback Mode-Locking Dynamics of a Directly-Modulated WRC-FPLD Fiber Laser

李宜錚(Yi-Cheng Lee)

指導教授 ： 林恭如

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.00891

摘要

本論文中我們利用自回授鎖模弱共振腔法布里-珀羅雷射建立一種新型光纖環形雷射，藉由直接調變弱共振腔法布里-珀羅雷射產生脈衝訊號的輸出，使得弱共振腔法布里-珀羅雷射在光纖環腔中同時被當作增益介質與脈衝光源來達到鎖模脈衝雷射。利用此架構建立一種在超過弱共振腔法布里-珀羅雷射原來頻寬的操作下，我們成功達到10 GHz鎖模脈衝雷射輸出。
首先，90%的回授功率以及28 dBm的調變強度經過自回授光纖環腔後可觀察到鎖模力量的增強，並建立在修正後中鎖模理論中進行探討。此外，經過系統優化後，我們討論了光脈衝輸出從自增益切換轉換至鎖模雷射的特性，使得弱共振腔法布里-珀羅雷射的縱模退化了30 dB，造成縱模的拓寬。而在自回授弱共振腔法布里-珀羅雷射鎖模光纖環形雷射脈衝輸出中，經優化後將弱共振腔法布里-珀羅雷射操作在60 mA與90%的自回授功率，可獲得最佳的脈衝寬、時基誤差、脈衝消光比與光譜線寬分別可達到22 ps、153 fs、13.65 dB以及7.6 nm脈衝輸出。
接著，我們同樣藉由光注入的理論模型模擬出光脈衝輸出從自增益切換轉換至鎖模雷射的情形，並改變不同的回授功率以及弱共振腔法布里-珀羅雷射的端面反射率探討脈衝之變化情形。透過脈衝形狀、縱模線寬以及啁啾頻率的改變，我們探討了在弱共振腔法布里-珀羅雷射的腔體與外環腔的競爭下所造成的鎖模力量變化。由於為了符合高密度分波多工器在傳輸上的應用，我們建立了雙環腔系統並且期望可同時達到品質好的脈衝訊號與選模的目的。然而，在原來90%自回授鎖模光纖雷射中，額外架設之外環腔會造成系統的調變頻寬下降，因而使得鎖模力量減弱，故我們藉由改變環腔功率的比例從10%增加到90%來觀察在共振條件改變時，探討光脈衝輸出品質的變化。所以，將雙環腔建構在自回授鎖模弱共振腔法布里-珀羅雷射系統中，脈衝弱化的情形使得無法針對高密度分波多工通道化的傳輸做探討。受到額外共振腔條件的影響，鎖模力量的弱化使得脈衝寬在雙環腔功率為10%與90%時，可分別得到脈衝寬為24 ps以及30 ps的脈衝輸出。
最後，我們探討90%強自回授鎖模弱共振腔法布里-珀羅雷射系統在外環腔以及直調雷射內腔競爭之行為。當我們些微改變雷射的調變頻率時，可觀察出光脈衝輸出頻率會從諧波鎖模轉變成一種高重複率的脈衝光源輸出。藉由改變系統的操作參數來觀察在環腔競爭後所產生的此一高重複率脈衝力量的來源，我們提出了一種新的自增益切換鎖模雷射技術。在將操作電流與頻率做微調整使得自增益切換鎖模力量增強的情況下，我們可以得到重複率高達67 GHz的脈衝光源輸出。

關鍵字

法布里-珀羅雷射二極體 ； 自回授 ； 直接調變 ； 鎖模 ； 自增益切換

並列摘要

In this work, a novel designed fiber ring laser by self-feedback mode-locked weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) is established. By directly-modulating, the WRC-FPLD is used simultaneously as the gain medium and the optical pulsed carrier source in the fiber ring. The characteristic of the 10 GHz mode-locked optical pulse-train beyond modulation bandwidth operation of the WRC-FPLD has been demonstrated.
First, with 90% self-feedback ratio and 28 dBm modulation power via circulated fiber ring, the enhancement of mode-locked force can be obtained, and the modification on the self-injection structure is discussed with the mode-locking theory. Besides, when optimizing the operation, the broadening longitudinal mode of the WRC-FPLD caused by the transformation from the gain-switching to mode-locking is demonstrated because of the degradation of the longitudinal mode suppression in 30 dB. The optimized mode-locking output of the self-feedback WRC-FPLD fiber ring with pulsewidth, timing jitter, pulse extinction ratio, and spectral linewidth of 22 ps, 153 fs, 13.65 dB, and 7.6 nm are obtained by setting the WRC-FPLD bias and self-feedback ratio at 60 mA and 90%, respectively.
Then, we also discuss the performance of output pulse on the transformation from gain-switching to mode-locking by changing the feedback ratio and reflectivity of the WRC-FPLD with the theoretic model of optical injection locking. By studying the conversion of pulse sharp, longitudinal mode linewidth, and frequency chirping, some trends of the competition between the intra-cavity of WRC-FPLD and external fiber ring can be explained by the enhancement of mode-locked force. In order to retain the better performance of optical pulsation and selective longitudinal mode frequency for DWDM channel spacing at the same time, the dual cavity built of an extra fiber ring is demonstrated. Under the 90% self-feedback mode-locked fiber ring laser, additional oscillation condition causes the variation on the modulation response of the system is proposed, which induces the change on the mode-locked force. When the different forces of oscillation are described by changing dual fiber ring ratio from 10% to 90%, the performance of optical pulsation can be observed. The self-feedback mode-locked WRC-FPLD in dual cavity which cannot implement the channelized transmission because of the degradation on the performance of optical pulse-train is also investigated. Moreover, the extra oscillation condition which causes the degeneracy on mode-locked force regardless of the dual cavity ratio of 10% or 90% would obtain the pulsewidth of 24 ps and 30 ps, respectively.
Finally, 90% self-feedback mode-locked WRC-FPLD with an external fiber ring has a competition with the intra-cavity of directly-modulated laser diode. Optical pulsation transferring from harmonic mode-locking to high-speed repetition rate is observed by detuning RF frequency under direct modulation. By means of changing the parameters of operation, the transformation from the competition can be demonstrated on another force, which means the domination of gain-switched mode-locking. The result of repetition rate enhancement up to 67 GHz is investigated and obtained by the adjustment on the biased current and frequency.

並列關鍵字

weak-resonant-cavity Fabry-Perot laser diode ； self-feedback ； directly-modulated ； mode-locking ； gain-switching

參考文獻

[1.1] G H C New, “The generation of ultrashort laser pulses”, Rep. Prog. Phys., vol. 46, no. 8, pp. 877-971, Aug. 1983.

[1.2] M. Didomenico, J. E. Geusic, H. M. Marcos, and R. G. Smith, “Generation of ultrashort optical pulses by mode locking the YAIG: ND laser”, Appl. Phys. Lett., vol. 8, no. 7 pp. 180-183, Apr. 1996.

[1.3] J. Hirano and T. Kimura, “Multiple mode locking of lasers”, IEEE J. Quantum Electron., vol. QE-5, no. 5, pp. 219-225, May 1969.

[1.4] Z. Chen, H. Sun, S. Ma, and N. K. Dutta, “Dual-wavelength mode-locked erbium-doped fiber ring laser using highly nonlinear fiber”, IEEE Photon. Technol. Lett., vol. 20, no. 24, pp. 2066-2068, Dec. 2008.

[1.5] A. Takada and H. Miyazawa, “30 GHz picosecond pulse generation from actively mode-locked erbium-doped fibre laser”, Electron. Lett., vol. 26, no. 3, pp. 216-217, Feb. 1990.