36 Gbit/s 16-QAM OFDM data transmission in DWDM-PON with a directly modulated and injection-locked WRC-FPLD

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= 3.8To 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.口試委員會審定書..............................................# 誌謝.......................................................i 中文摘要...................................................ii ABSTRACT..................................................iv CONTENTS..................................................vi LIST OF FIGURES...........................................ix Chapter 1 Introduction...............................1 1.1 Overview of transmitters in DWDM-PON..............1 1.2 Motivation........................................2 1.2.1 High-speed transmission based on colorless transmitter...............................................2 1.2.2 Cost-effective injection-locked scheme in DWDM-PON.......................................................3 1.2 Thesis Architecture...............................5 Chapter 2 Up-shifting the relaxation oscillation induced relative intensity noise spectrum of a directly modulated and injection-locked WRC-FPLD for 20-Gbit/s 16-QAM OFDM transmission..........................................6 2.1 Introduction.......................................6 2.2 Experimental Setup.................................6 2.3 Results and Discussions............................9 2.3.1 Theories of the injection-locked WRC-FPLD..........9 2.3.2 The enhancement of the signal-to-noise ratio (SNR) by injection-locking......................................14 2.3.3 The BER reduction of the 16-QAM OFDM data carried by the injection-locked WRC-FPLD.............................16 2.3.4 Directly modulating a WRC-FPLD with pre-leveled OFDM data......................................................19 2.4 Summary...........................................21 Chapter 3 Master-to-slave injection-locked WRC-FPLD pair with 28 DWDM-PON channels for 16-QAM OFDM transmission at 20 Gbit/s over 25-km SMF...............................23 3.1 Introduction......................................23 3.2 Experimental setup................................24 3.3 Results and discussion............................26 3.3.1 The spectra of the master, slave and injection-locked slave WRC-FPLD.....................................26 3.3.2 The comparison between WRCFPLD-to-WRCFPLD pair and DFBLD-to-WRCFPLD pair.....................................29 3.3.3 Wavelength locking range of the injection-locked WRC-FPLD..................................................30 3.3.3 Pre-leveling for back-to-back and 25-km SMF 16-QAM OFDM transmission.........................................31 3.3.4 BER vs. receiving power anaysis of the 16/64-QAM OFDM transmission.........................................33 3.3.5 Multi-channels demonstration of master-to-slave injection-locked WRC-FPLD pair for transmitting the 16-QAM OFDM signal...............................................34 3.4 Summary...........................................37 Chapter 4 Directly modulating a 10-GHz TO-56-can packaged WRC-FPLD with 16-QAM OFDM at 36 Gbit/s over 25-km SMF.......................................................38 4.1 Introduction......................................38 4.2 Experimental Setup................................39 4.3 Results and Discussions...........................43 4.3.1 Frequency response of the injection-locked WRC-FPLD......................................................43 4.3.2 Direct 16-QAM OFDM encoding of an injection-locked WRC-FPLD packaged with a 10-GHz TO-56-can.................47 4.3.3 3-D BER contour for finding the optimized operating point of the injection-locked WRC-FPLD....................51 4.3.4 Pre-amplified 16-QAM OFDM data transmitted by an injection-locked and 10-GHz TO-can packaged WRC-FPLD......55 4.4 Summary...........................................58 Chapter 5 Conclusion................................60 REFERENCE.................................................6

Key Signal Processing Technologies for High-speed Passive Optical Networks

With emerging technologies such as high-definition video, virtual reality, and cloud computing, bandwidth demand in the access networks is ever-increasing. Passive optical network (PON) has become a promising architecture thanks to its low cost and easy management. IEEE and ITU-T standard organizations have been standardizing the next-generation PON, targeting on increasing the single-channel capacity from 10 Gb/s to 25, 50, and 100 Gb/s as the solution to address the dramatic increase of bandwidth demand. However, since the access network is extremely cost-sensitive, many research problems imposed in the physical layer of PON need to be addressed in a cost-efficient way, which is the primary focus of this thesis. Utilizing the low-cost 10G optics to build up high-speed PON systems is a promising approach, where signal processing techniques are key of importance. Two categories of signal processing techniques have been extensively investigated, namely optical signal processing (OSP) and digital signal processing (DSP). Dispersion-supported equalization (DSE) as a novel OSP scheme is proposed to achieve bit-rate enhancement from 10 Gb/s to 25 Gb/s based on 10G class of optics. Thanks to the bandwidth improved by DSE, the non-return-zero on-off keying which is the simplest modulation format is able to be adopted in the PON system without complex modulation or DSP. Meanwhile, OSP is also proposed to work together with DSP enabling 50G PON while simplifying the DSP complexity. Using both DSE and simple feed-forward equalizer is able to support 50 Gb/s PAM-4 transmission with 10G optics. For C-band 50 Gb/s transmission, injection locking techniques as another OSP approach is proposed to compress the directly modulated laser chirp and increase system bandwidth in the optical domain where a doubled capacity from 25 Gb/s to 50 Gb/s over 20 km fiber can be built on top of 10G optics. For DSP, we investigated the advantages of neural network (NN) on the mitigation of the time-varying nonlinear semiconductor optical amplifier pattern effect. In order to reduce the expense caused by the high computation complexity of NN, a pre- equalizer is introduced at the central office that allows cost sharing for all connected access users. In order to push the PON system line rate to 100 Gb/s, a joint nonlinear Tomlinson- Harashima precoding-Volterra algorithm is proposed to compensate for both linear and nonlinear distortions where 100 Gb/s PAM-4 transmission over 20 km fiber with 15 GHz system bandwidth can be achieved