- 學位論文
超頻寬非歸零訊號直調以TO-can封裝之長共振腔與低端面反射率二極體雷射於分波多工被動光網路系統之分析
Over Bandwidth NRZ Modulation of TO-can Packaged Long-cavity Colorless Laser Diodes with Low Front-facet Reflectance for DWDM-PON Systems
摘要
分波多工光網路系統(WDM-PON)因其諸多優點已被視為因應未來需求的最佳選擇，為了降低成本、提高應用的可能性，有許多為了分波多工光網路的光源被提出，例如單模雷射、反射式的被導體放大器、利用放大後的自發輻射光源(ASE)注入鎖模的、相互注入的費比布洛雷射等等。我們使用的長共振腔無色費比布洛雷射(long-cavity colorless laser diode)是一種降低端面反射率和增加共振腔長的費比布洛雷射，因此相較於一般費比布洛雷射具有寬頻譜的優點，相較於反射式的被導體放大器則具有較好的同調性。本篇論文首先討論不同的低端面反射率值對做為傳訊器的雷射特性的影響，在可調式雷射注入鎖模後長共振腔無色費比布洛雷射的傳輸表現，其直接調變速率為2.5 Gbit/s。當端面反射率從0.2%增加至1.2%，訊雜比(SNR)和ER可分別增加8.3%和8%，而在誤碼率(BER)為10-9情況下，接收功率分別為-26.4 dBm (0.2%)和-27.9dBm (1.2%)。除此之外，我們也嘗試使用長共振腔無色費比布洛雷射在高速調變的分波多工光網路系統中作為傳訊器，其調變速率為10Gbit/s，同時，我們也進一步討論注入功率大小對傳輸表現的影響。為了降低外來元件對頻寬的影響，我們將雷射接腳剪短、連接SMA接頭，在直接連接PRBS訊號產生器，其中並未再使用bias tee。當注入功率從-12dBm調整至-3 dBm時可有效抑制側模功率，將側模抑制比從39 dB提高至50 dB。在注入功率為-3 dBm的情況下，接收功率為-12.2 dBm時可達到BER為10-9。為了更仔細探討端面反射率與注入功率對雷射頻率響應的影響，依據雷射的速率方程式(rate equations)，我們使用MATLAB程式模擬不同緞面反射率及不同注入功率下的雷射頻響。在相同操作電流比例下(Ibias/Ith)，低端面反射率的雷射具有略佳的頻寬，而注入功率也有一定有效範圍。最後，為了改善長共振腔無色費比布洛雷射溫度無法被控制的問題，我們設計新的mount使其在操作上更容易被注入鎖模，以避免先前誤碼率量測時出現的floor問題。在WDM-PON系統中直接調變10Gbit/s長共振腔無色費比布洛雷射，其ER可達到6.95 dB、SNR可達到6.18 dB，而接收功率為-15.4 dBm下誤碼率為10-9。經過25公里色散位移光纖後，誤碼率10-9時有3.8 dB功率懲罰。
並列摘要
In this thesis, the long-cavity colorless laser diodes with different front-facet reflectance are employed to perform the wavelength injection-locked on-off-keying data transmission. By changing front-facet reflectance from 0.2% to 1.2%, the received OOK data improves both signal-to-noise ratio (SNR) and extinction ratio (ER) by 8.0% to enhance the Q factor by 6.3%, which benefits bit-error-rate (BER) reduction by more than two orders of magnitude. As the injection-locking power is raised from -6 to -3 dBm, the receiving power sensitivity of the long-cavity colorless laser diode is improved from -27.9 to -29.2 dBm at BER of 10-9. However, the long-cavity colorless laser diode with a lower front-facet reflectance shows an opposite trend. The injection-locking induced enhancement is limited within a frequency region controlled by the injection power, which results from a large disparity between continuous-wave injection and stimulated emission inside the long-cavity colorless laser diode. Next, a 600-um long-cavity laser diode with 2% low front-facet reflectance is demonstrated as a colorless OC-192 transmitter for the future DWDM-PON, which is packed in a TO-56-can package of only 4-GHz frequency bandwidth but can be over-bandwidth modulated with 10-Gbit/s non-return-to-zero (NRZ) data-stream. The coherent injection-locking successfully suppresses its side-mode intensity and noise floor level, and improves its modulation throughput at higher frequencies. With increasing the coherent injection-locking power from -12 to -3 dBm, the side-mode suppression ratio significantly increases from 39 to 50 dB, which also suppresses the frequency chirp from -12 to -4 GHz within a temporal range of 150 ps. Such an over-bandwidth modulated laser diode still exhibits an on/off extinction ratio of 6.68 dB and a signal-to-noise ratio of 4.96 dB, which can provide a back-to-back receiving power via sensitivity of -12.2 dBm at BER of 10-9. Furthermore, the effect of different front-facet reflectance and injection power are analyzed theoretically based on rate equations. In free-running case, the long-cavity laser diode with a lower front-facet reflectance possesses not only a broader spectrum but a larger modulation bandwidth under a fixed bias current ratio (Ibias/ Ith) operation. Implementing an appropriate amount of injection power, the relaxation resonance frequency and the damping rate can be enhanced owing to the additional coupling of photon density to the phase of the injection -locked laser. In fact, the over-injected and unmodulated photons are unable to create more stimulated emission photons but being noise component in the cavity. By equipping the long-cavity laser diode with temperature control device, the long-cavity colorless laser diode transmitter demonstrates a better transmission performance in WDM-PON system with bit rate of 10 Gbit/s. At back-to-back transmission case, the receiving power sensitivity at BER of 10-9 is -15.4 dBm with ER of 6.95 dB and SNR of 6.18 dB. After 25-km DSF transmission, the receiving power sensitivity slightly degrades to -11.6 dBm at a requested BER of 10-9.