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標題: | 預補償分頻多工演算法於高位元率資料中心光傳輸 Pre-compensated Frequency Division Multiplexing Algorithms for High-data-rate Optical Transmission in Data Centers |
作者: | Wei-Li Wu 吳偉立 |
指導教授: | 林恭如(Gong-Ru Lin) |
關鍵字: | 垂直共振腔面射型雷射,外調電致吸收調變雷射,電致吸收調變器,分佈反饋式雷射,M階正交振幅調變,正交分頻多工,預失真訊號處理,廣義分頻多工,離散多載波,適應性位元演算法,短距離資料中心,長距離資料中心, vertical cavity surface emitting laser (VCSEL),external modulation laser (EML),electro-absorption modulator (EAM),distributed feedback laser diode (DFBLD),M-ary quadrature amplitude modulation (M-ary-QAM),orthogonal frequency division multiplexing (OFDM),pre-distortion,generalized frequency division multiplexing (GFDM),discrete multi-tone (DMT),bit-loading,intra-data-center,inter-data-center, |
出版年 : | 2019 |
學位: | 碩士 |
摘要: | 下一世代資料中心將面臨到串流多媒體、物聯網及雲端運算的快速發展,在可預見的未來,人工智慧技術的大量數據處理也將推動光數據流量進入佑位元組(yottabyte)時代,對於更具成本效益超高速光收發模組搭配更高頻譜利用效率的調變格式的需求已經迫在眉睫,為了滿足未來資料中心對計算資源的巨大需求,2017年電機電子工程學會乙太網規格(IEEE P802.3bs)已經針對短距離及長距離的資料中心分別制定了400GBASE-SR16及400GBASE-LR8規範,然而直到如今,在固有頻寬的光源達到最大的傳輸速度及容量仍存在不少挑戰性。因此,在此篇論文中將提出並展示許多更具前瞻性的傳輸格式應用於直調垂直共振腔面射型雷射(VCSEL)於短距離資料中心及外調電致吸收調變雷射(EML)於長距離資料中心來滿足未來大數據的需求。
針對短距離資料中心,在此次實驗中利用正交振幅調變-正交分頻多工(QAM-OFDM)、廣義分頻多工(GFDM)及離散多載波(DMT)格式直接調變850奈米波段之雙層氧化物限制孔徑VCSEL於背對背及100公尺OM5多模光纖。在此3.5微米孔徑VCSEL結構中利用InGaAs/AlGaAs多量子阱和雙層氧化物限制孔徑增強其微分增益、降低熱阻及改善其寄生電阻電容來提供更高的調變頻寬。優化於9 mA (11倍閾值電流)可以提供3-4個橫向模態、24.9 GHz的3 dB頻寬及抑制到-138.0 dBc / Hz相對強度雜訊。透過預均衡及預調平兩種數位訊號處理技術於OFDM可以補償傳輸訊雜比之衰退,並實現高達160 Gbit/s背對背及140 Gbit/s 100公尺OM5多模光纖。GFDM透過將N個OFDM子載波劃分為K個相等大小的GFDM子載波和M個相等大小的GFDM子符元結構,可以有效將頻外抑制 (OOB)增強到35.9 dB及降低峰值平均功率比(PAPR)至9.7 dB,並實現高達168 Gbit/s位元傳輸率於背對背及146 Gbit/s 100公尺OM5多模光纖,並可以在140 Gbit/s位元傳輸下達到最低接收功率罰損至3.5 dB。為了實現最大頻譜使用效率,更採用適應性位元演算法於DMT將背對背及100公尺OM5位元傳輸率表現有效提升至172 Gbit/s及146 Gbit/s,從而實現超高數據容量短距離資料中心鏈結。 針對長距離資料中心,在此次實驗中利用的光源是商用1307奈米波段電致吸收調變器(EAM)及分佈反饋式雷射(DFBLD)晶片自製光傳輸模組而成的EML,透過更高頻譜利用效率的QAM-OFDM、GFDM及DMT傳輸格式可以在背對背及10公里單模光纖透過外部調變將有限頻寬低於30 GHz之EAM-DFBLD有效提升其傳輸速度及容量。此光源在操作偏流及偏壓分別優化於100 mA及-1.5 V時具備高達大於50 dB側模抑制比及抑製到-142.0 dBc/Hz相對強度雜訊。使用預均衡及預調平之OFDM傳輸格式可以有效提供將背對背的位元傳輸率達到160 Gbit/s及在10公里單模光纖達到148 Gbit/s,同時在140 Gbit/s位元傳輸下達到最低接收功率罰損至0.06 dB。與未使用任何預失真的OFDM格式相比,GFDM可以有效改善OOB及PAPR並在背對背及10公里單模光纖達到150 Gbit/s及138 Gbit/s傳輸速率並在140 Gbit/s傳輸條件下改善0.25 dB功率罰損。利用適應性位元演算法於DMT找出最佳化之子載波所搭配之M階QAM數組合,可以將背對背及10公里單模光纖傳輸速率提高至164 Gbit/s及157 Gbit/s,從而實現超高數據容量長距離資料中心鏈結。 Data center of the next generation will face the rapid development of multimedia streaming, internet of things and cloud computing. In the foreseeable future, huge amounts of data processing for artificial intelligence technology will push the optical data traffic to the yottabyte era, and the need for more cost-effective ultra-high speed optical transceivers with higher spectral-usage-efficient modulation schemes has been already imminent. To satisfy the tremendous need on computing resources from future data centers, the 400GBASE-SR16 for short-reach intra-data-center and 400GBASE-LR8 for long-reach inter-data-center have already been formulated by IEEE P802.3bs in 2017. However, until now, the maximum transmission speed and capacity of the optical source with inherent bandwidth-limitation still exist many challenges. In this thesis, the more prospective and advanced data formats carried by directly modulated vertical cavity surface emitting laser (VCSEL) in short-reach intra-data-center and externally modulated electro-absorption modulated laser (EML) in long-reach inter-data-center will be proposed and demonstrated for supporting heavy data traffic in the future. For short-reach intra-data-center, delivering quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM), generalized frequency division multiplexing (GFDM) and discrete multi-tone (DMT) data streams carried by a bi-layer oxide confined 850-nm VCSEL are demonstrated under back-to-back (BtB) and 100-m OM5-MMF. The 3.5-μm-aperture VCSEL contains InGaAs/AlGaAs multiple quantum wells and bi-layer oxide-confined aperture to enhance its differential gain, reduce its thermal resistance, and improve the parasitic capacitance and resistance. Optimizing the VCSEL bias at 9 mA (11 Ith) makes its lasing with 3-4 transverse modes and provides its 3-dB bandwidth of 24.9 GHz and suppressed RIN level of -138.0 dBc/Hz. With using pre-distortion technique including pre-equalization and pre-leveling on the OFDM to compensate the SNR degradation, the OFDM can provide 160 Gbit/s for BtB and 140 Gbit/s for 100-m OM5-MMF transmissions. By dividing the N OFDM subcarriers into K equal-sized GFDM subcarriers and M equal-sized GFDM subsymbols, the QAM-GFDM can effectively enhance the out-of-band (OOB) suppression to 35.9 dB and reduce the peak-to-average-power ratio (PAPR) to 9.7 dB, which can support 168 Gbit/s under BtB and 144 Gbit/s in 100-m OM5-MMF transmissions with a receiving power penalty of 3.5 dB. To achieve the maximal spectral-usage efficiency, the DMT with the adaptive bit-loading algorithm is employed to improve the data rate up to 172 Gbit/s for BtB and 146 Gbit/s for 100-m OM5-MMF conditions for supporting ultrahigh-speed intra-data-center links. For long-reach intra-data-center, employing high-spectral-efficient QAM-OFDM, GFDM and bit-loaded DMT data formats carried by the commercially available 1307-nm electro-absorption modulator integrated with distributed feedback laser (EAM-DFBLD) with finite bandwidth below 30 GHz can achieve ultrahigh capacity data link. By optimizing the EAM-DFBLD transmitter with Ibias=100 mA and VEA=-1.5 V, the EAM-DFBLD can exhibits higher than 50 dB side mode suppression ratio and suppressed RIN of -142.0 dBc/Hz, which can deliver pre-distorted OFDM up to 160 Gbit/s for BtB and 148 Gbit/s for 10-km SMF transmissions and remain their data rates at 140 Gbit/s with reduced receiving power penalty of 0.06 dB. In comparison of OFDM, GFDM carried by the EAM-DFBLD can effectively improve the PAPR and OOB and provide 149.6 Gbit/s under BtB and 138 Gbit/s in 10-km SMF transmission links with better power penalty than OFDM by -0.25 dB. The adaptive bit-loading algorithm applied for the DMT transmission can find out the optimized composition of M-QAMs with dependent subcarriers, which improves the data rate up to 164 Gbit/s for BtB and 157 Gbit/s for 10-km SMF transmission for future inter-data-center application. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/74370 |
DOI: | 10.6342/NTU201902267 |
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顯示於系所單位: | 光電工程學研究所 |
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