36 Gbit/s 16-QAM正交分頻多工直調注入鎖定弱腔雷射二極體傳輸於高密度分波多工被動光纖網路

Abstract

為了要建構一個高速且低成本的光纖網路，將多載波訊號格式結合低成本之光源應用於高密度分波多工被動網路(DWDM-PON)將是未來重要的趨勢。我們將一端面反射率降低至1%之弱共振腔法布里-珀羅雷射二極體(WRC-FPLD)應用於DWDM-PON，並利用注入鎖定提升WRC-FPLD的弛張震盪頻率並降低其相對強度雜訊(RIN)，成功地直接調變正交幅度調制 (QAM) 正交分頻多工 (OFDM) 之調變格式並達到其調變速率為20 Gbit/s。當注入光功率由 -12 dBm增加到 -3 dBm 時，可以有效地降低WRC-FPLD的臨界電流，使其弛張震盪頻率由5 GHz提升至7.5 GHz. 這會同時造成在信號調變頻寬中的相對雜訊強度下降，並會將訊號雜訊比(SNR)由16 dB提升至20 dB，使得其16-QAM OFDM信號傳輸之誤碼率(BER)可被有效地降低。藉由利用預先斜率補償 (pre-leveling)的方法補償雷射自然頻率響應的衰減，可進一步地提升傳輸品質。 為了要更進一步地降低注入光源在整個傳輸系統架構中的成本，我們提出了部分同調光源WRC-FPLD注入WRC-FPLD之主從注入架構，達成20 Gbit/s之16-QAM OFDM於25公里單模光纖傳輸，藉由主從注入架構，16-QAM OFDM傳輸25公里單模光纖後，其誤碼率可由1.4x10^-1被降低至 1.2x10^-3，經由預先斜率補償技術可進一步降低誤碼率至2.1x10^-4，在此條件操作下，可實現28個高密度被動光纖網路通道，且各通道之誤碼率皆小於前向錯誤更正之要求 (FEC-limit, BER= 3.8

To build up a high-speed and low-cost optical access network, it is necessary to fuse a multiple carrier data format and a colorless transmitter based universal into the dense wavelength division multiplexing passive optical network (DWDM-PON) in the near future. The directly modulated transmission of optical 16 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) data-stream at its total bit rate up to 20 Gbit/s is demonstrated by up-shifting the relaxation oscillation peak and suppressing its relative intensity noise in a weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) under injection-locking. With increasing the injection-locking power from -12 to -3 dBm, the effective reduction on threshold current of the WRC-FPLD significantly shifts its relaxation oscillation frequency from 5 to 7.5 GHz. This concurrently induces an up-shift of the peak relative intensity noise (RIN) of the WRC-FPLD, and effectively suppresses the background RIN level within the OFDM band between 3 and 6 GHz. The enhanced signal-to-noise ratio from 16 to 20 dB leads to a significant reduction of bit-error-rate (BER) of transmitted 16-QAM-OFDM data. After pre-leveling the peak amplitude of the OFDM subcarriers to compensate the throughput degradation of the directly modulated WRC-FPLD, the BER under 25-km SMF transmission can be further improved. To further reduce the cost of the injection-locking master source, the partially coherent WRC-FPLD pair under master-to-slave injection-locking operation is demonstrated for optical 16-QAM OFDM transmission at 20 Gbit/s over 25-km SMF in DWDM-PON with 28 affordable channels achieving BER of below FEC-limit. After master-to-slave injection-locking, the BER of the 16-QAM OFDM data stream under back-to-back and 25-km transmissions can be improved from 3.3x10^-3 to 2.1x10^-5 and from 1.4x10^-1 to 1.2x10^-3, respectively. With OFDM subcarrier pre-leveling, the BER of 16-QAM OFDM data transmitted by the master-to-slave injection-locked WRC-FPLD over 25-km transmission is further improved from 1.2x10^-3 to 2.1x10^-4, concurrently enabling the 28 channel transmissions at 20 Gb/s with BER below FEC-limit of 3.8x10^-3. Moreover, the overall frequency bandwidth of the TO-can packaged colorless WRC-FPLD can be extended from 5 to 9 GHz by replacing the package of the colorless WRC-FPLD from a typical 4-GHz TO-56-can to a 10-GHz TO-56-can. By injection-locking the WRC-FPLD based colorless transmitter packaged in a 10-GHz TO-56-can, the premier demonstration on directly modulated of 16 QAM OFDM transmission up to 36 Gbit/s per channel is demonstrated. The compromised optimization on enlarged modulation bandwidth and declined throughput power of the WRC-FPLD under strong injection-locking is considered, and the trade-off between the RIN suppression and the frequency response degradation with detuning the injection level is discussed. By pre-amplifying the directly modulated optical 16-QAM OFDM data stream covering a bandwidth up to 9 GHz with total raw bit rate of 36 Gbit/s, the receiving bit error rate (BER) under back-to-back transmission can be further reduced from 3.4x10^-3 to 2.1x10^-4. This enables the 36-Gbit/s 16-QAM OFDM transmission over 25-km SMF with its BER matching the FEC criterion at a receiving power of -3 dBm.