同調注入鎖模弱共振腔雷射二極體之直調正交分頻多工傳輸於分波多工被動光纖網路

A coherently injection-locked weak-resonant-cavity FPLD with direct orthogonal frequency division multiplexing for transmission in WDM-PON

李益丞(Yi-Cheng Li)

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(2012年)

https://doi.org/10.6342/NTU.2012.00556

摘要

為了因應高速率網路的要求，應用分波多功器的被動光纖網路 (DWDM-PON)於光纖到家的系統中，顯然是一個可行的方法。為了降低 DWDM-PON 光纖網路系統的成本，我們使用以端面1% 反射率的弱共振腔法布里-貝羅雷射(WRC-FPLD)為傳輸器，並且使用高頻寬使用率的正交分頻多工 (OFDM) 混和正交幅度调制（QAM）之調變格式，分析不同操作條件並優化最好的操作條件。
我們成功的實驗出高速率20 Gbit/s 的 OFDM-PON 應用於直調WRC-FPLD，並且利用頻率軸斜率補償 (pre-leveling)的方法補償雷射自然頻率響應的衰減，並且獲得錯誤向量強度(EVM)為12%，也可以在-8 dBm 的接收功率下達到先行誤碼更正限制(FEC limit) 3.8E-3 和接收功率在 -2 dBm 下得到誤碼率 4.5E-5 的效果。並且在傳送速率於12 Gbit/s 的 16-QAM-OFDM 下討論操作參數，再注入光率達到 -9 dBm，操作電流為 30 mA以及前置放大倍率為 5dB下達到消光比 (ER) 6 dB，在25公里傳輸後獲得接收功率 -7 dBm下誤碼率為 3.6×10-7的表現。最後，因應高速率雙向傳輸系統的需求，我們提出下行訊號以分布回饋式半導體雷射，上行訊號為WRC-FPLD的雙向傳輸系統，利用餘裕的下行光源注入 WRC-FPLD，並且討論了下行訊號接收/反射的比率，成功的在無額外注入光源裝置的情況下達到16/64-QAM-OFDM的雙向傳輸。

關鍵字

雷射 ； 正交分頻多工 ； 被動光纖網路

並列摘要

In order to meet the demands of high speed optical fiber communication in the near future, the dense-wavelength-division-multiplexing passive-optical-network (DWDM-PON) has been regarded as the promising solution. Recently, the weak-resonant-cavity fabry-perot laser diode (WRC-FPLD) was made to meet the requirements of the unified transmitters for DWDM-PON systems, which exhibits a broadband gain spectrum with tiny longitudinal modes to support different wavelength channels via the external photon injection technique. In this work, the coherent injection-locking and direct modulation of a long-cavity colorless WRC-FPLD with 1% end-facet reflectance and weak-resonant longitudinal modes is employed as an universal optical transmitter to demonstrated for optical 16-quadrature amplitude modulation orthogonal frequency division multiplexing (QAM-OFDM) transmission over 25 km in a DWDM-PON system.
The maximum transmission bit-rate of 20-Gbit/s is improved by fusing the OFDM spectral pre-leveling with the coherent injection-locking techniques in a directly modulated WRC-FPLD. The OFDM spectral pre-leveling effectively compensate the finite bandwidth and unflattened modulating response of the injection-locked WRC-FPLD to improve the transmission error vector magnitude (EVM) and signal-to-noise ratio (SNR) performances. The received constellation plot reveals that the EVM and SNR of the back-to-back transmitted 16-QAM-OFDM data are significantly improved to 14.12%. With the use of both injection-locking and pre-leveling techniques, the directly 16-QAM-OFDM modulated WRC-FPLD transmitter can reach the FEC limited BER of 3.8E-3 at a receiving power sensitivity of -8 dBm. The OFDM spectral pre-leveling technique helps the WRC-FPLD to reduce the overall BER of 16-QAM-OFDM data by one order of magnitude, providing a minimum BER of 3E-5.
Moreover, we discussed the trade-off between each operation parameters such as injection power, bias current and electrical OFDM waveform amplification. The optimized bias current of 30 mA (~1.5Ith) with corresponding extinction ratio (ER) of 6 dB and the external injection power of -9 dBm is required for such a WRC-FPLD to OFDM data-stream. By increasing external injection-locking from -9 dBm to 0 dBm, the peak-to-peak chirp of the OFDM data stream reduces from 7.7 to 5.4 GHz. The side mode suppression ratio (SMSR) of up to 50 dB is achieved. Such a universal colorless DWDM-PON transmitter can deliver the optical OFDM data-stream at 12 Gbit/s QAM-OFDM data after 25-km transmission with a receiving power sensitivity of -7 dBm at bit-error-rate (BER) of 3.6E-7 when pre-amplifying the OFDM data by 5 dB.
To fulfill the bi-directional transmission by using injection locked WRC-FPLD as up-stream transmitter, a full-duplex 16/64-QAM-OFDM passive optical network at bit rate of 12/18 Gbit/s based on the down-stream DFBLD/EAM and up-stream injection-locked colorless WRC-FPLD transmitter is demonstrated in the last chapter. After 25-km SMF transmission, the down-stream 16-QAM OFDM data shows clear constellation plot with the lowest BER of 3.09E-7 at a receiving power of -6.3 dBm. In contrast, the down-stream pre-amplified 64-QAM OFDM data can reach the FEC required BER of 3.8E-3 at -7.3 dBm. The corresponding SNR of the 25-km SMF transmitted 64-QAM-OFDM data carried by the directly modulated colorless FPLD can be optimized to 22.9 dB.
Based on our proposed full-duplex system based on up-stream injection locked WRC-FPLD transmitter, the injection-locked laser diode based bi-directional transmission without any external injection light source is demonstrated, and become a feasible solution for DWDM-PON.

並列關鍵字

laser ； orthogonal frequency division multiplexing ； passive-optical-network

參考文獻

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