高速850-nm垂直共振腔面射型雷射與多模光纖短程通信網路

Abstract

隨著雲端運算及大數據應用快速的發展，人們對於高資料速率串流的需求以驚人的速度在增長。為了滿足這樣嚴苛的要求，單通道50 Gbit/s的200GBASE-SR4及 單通道25 Gbit/s的400GBASE-SR16的乙太網規格分別被電機電子工程師學會(IEEE) P802.3cd 及 IEEE P802.3bs專案小組所制定。在未來，高達1.6 Tbit/s的需求可以被預期。因此，研發單通道100 Gbit/s的光發送器是必須的。在本論文中展示了以垂直共振腔面射型雷射(VCSEL)高資料速率調變四階脈衝強度調變(PAM-4)及正交幅度調制(QAM)正交分頻多工(OFDM)通過新一代多模光纖應用於短距離資料中心。 在此實驗中，透過調變單模及少模VCSELs傳輸PAM-4及16-QAM OFDM資料格式比較了OM5及OM4多模光纖的傳輸性能。而此雙層氧化孔徑為3微米的單模VCSEL展現了0.04奈米的半高全寬(FWHM)及0的均方根譜線寬度(RMS)的單橫模譜線。當操作電流在十倍偏壓電流時，其3-dB類比頻寬為21.4 GHz及相對強度雜訊(RIN)為-138 dBc/Hz的特性可以支持高速率的訊號調變。在更換一百公尺的OM4至OM5多模光纖後，在KP4前向錯誤更正(KP4-FEC)的標準下且預失真過後可以達成接收功率罰損為0.12 dB且眼圖對稱的64-Gbit/s PAM-4資料傳輸。相較於OM4多模光纖，OM5多模光纖因為其較高的有效模態頻寬及較低的色度色散可以明顯的提升傳輸表現。不僅如此，在偏壓電流優化後及預補償後，接收功率罰損為0.1 dB的96-Gbit/s 16-QAM OFDM 資料傳輸通過一百公尺OM5多模光纖在FEC的標準下可以被實現。 而氧化孔徑為5微米的少模VCSEL展現了臨界電流為0.25毫安培及光功率為1.2毫瓦的特性。且當操作在8毫安培時，其阻抗為60歐姆及3-dB頻寬為24 GHz。而少模VCSEL傳輸32 GBaud的PAM-4訊號在通過一百公OM5多模光纖相較於OM4多模光纖展現了更清楚的眼圖及更寬的抖動容忍度。更甚者，64 Gbit/s的資料傳輸功率罰損也從3.41 dB減少至0.86 dB。其主因是因為OM5多模光纖相較於OM4多模光纖擁有較低的模態色散及較高的有效模態頻寬。此外，調變16-QAM OFDM於少模VCSEL經過背對背在高溫操作下從25度到85度時也被討論。在經過偏壓電流為8毫安培(32倍偏壓電流)及預補償斜率為0.5 dB/GHz的優化後，120-Gbit/s 的16-QAM OFDM背對背傳輸在FEC下透過少模VCSEL可以被實現。而接收功率罰損為3.78 dB的104 Gbit/s 16-QAM OFDM資料傳輸通過一百公尺OM5多模光纖後也被成功實現。 最後，不同的氧化孔徑為5.5及7.5微米VCSEL的基本特性及傳輸表現被進行比較。7.5微米孔徑的VCSEL展現了較高的光功率及量子效率，但其3-dB頻寬較窄且相對強度雜訊也較高。而擁有較高3-dB頻寬為25.2 GHz及較低的相對強度雜訊為-135 dBc/Hz的5.5微米孔徑VCSEL透過調變PAM-4和16-QAM OFDM可以支持最高的資料速率達到84和140 Gbit/s的背對背資料傳輸。在通過一百公尺OM5多模光纖後，80和120 Gbit/s的PAM-4和16-QAM OFDM資料傳輸可以被成功的達成且其接收功率罰損分別為3.24及3.1 dB。

With the rapid development of the cloud computing and the big data application, the demanding of the high-speed data stream has risen at an incredible rate in recent year. To fulfill such rigorous requirement, the latest standards of Ethernet have been established as 200GBASE-SR4 with 50 Gbit/s per channel by IEEE P802.3cd task force and 400GBASE-SR16 with 25 Gbit/s per channel by IEEE P802.3bs task force. In the near future, it can be expected that the requirement will be rising up to 1.6 Tbit/s. Therefore, it is necessary to develop the 100 Gbit/s per channel for optical transmitters. The high-speed data modulation for the short-reach data center application with the four-level pulse amplitude modulation (PAM-4)/16-level quadrature amplitude modulation orthogonal frequency-division multiplexing (16-QAM OFDM) carried by vertical cavity surface emitting laser (VCSEL) through new generation of multi-mode fiber (MMF) are demonstrated in this thesis. The comparison on transmission performance of the OM5-MMF and OM4-MMF for the PAM-4/16-QAM OFDM data format carried by single-transverse-mode (SM) and few-transverse-mode (FM) vertical cavity surface emitting laser (VCSEL) are discussed in this experiment. The SM-VCSEL with the double oxide-confinement aperture size of 3 um exhibit the only one transverse mode lasing with full width at half maximum (FWHM) of 0.04 nm and root-mean-square (RMS) spectra width of 0. When biasing at 10 Ith, the 3-dB analog bandwidth of 21.4 GHz and the relative intensity noise (RIN) of -138 dBc/Hz can support the high-speed signal modulation. After the replacement for the MMFs from 100-m OM4 to OM5, the transmission performance of pre-emphasized 64-Gbit/s PAM-4 data transmission can be achieved with the symmetric eye diagram under the KP4-forward error correction (KP4-FEC), which reveals the receiving power penalty of 0.12 dB. It is mainly due to lower chromatic dispersion and higher effective modal bandwidth (EMB) for OM5-MMF as compared to OM4-MMF for the data carried by SM-VCSEL. Nevertheless, the 96-Gbit/s data transmission for 16-QAM OFDM can also be achieved by passing through 100-m OM5-MMF after the bias current optimization and pre-leveling with the receiving power penalty of 0.1 dB under the FEC criterion. For the bare FM-VCSEL chip, the low threshold current of 0.25 mA and the high optical power of 1.2 mW with the oxide-confined aperture of 5 μm are declared. The impedance of 60 ohm and the 3-dB bandwidth of 24 GHz are displayed at the DC bias of the 8 mA. With the pre-emphasis technique, the FM-VCSEL transmitting the 32 GBaud PAM-4 data shows the clear eye diagram and wider jitter tolerance by passing through 100-m OM5-MMF as compared to 100-m OM4-MMF. Furthermore, the receiving power penalty of at least 3.41 dB reduce to 0.86 dB for the 64 Gbit/s PAM-4 data stream. The lower modal dispersion and higher EMB of the OM5-MMF exhibit the better transmission performance as compared to OM4-MMF for the data transmitted by the FM-VCSEL. In addition, the high temperature operations from 25oC to 85oC at the condition of back-to-back (BtB) were also discussed with the FM-VCSEL chip carrying the 16-QAM-OFDM data. With the bias current optimization at 8 mA and pre-leveling slope of 0.5 dB/GHz, the 120 Gbit/s 16-QAM OFDM BtB data transmission can be achieved with the criterion of FEC for the FM-VCSEL. After propagating through 100-m-long OM5-MMF, the FM-VCSEL successfully exhibit the 104 Gbit/s transmission with a receiving power penalty of 3.78 dB. Finally, the MM-VCSELs with different oxide-confined aperture size of 5.5-m and 7.5-m is compared through the basic characteristic and transmission performance. The 7.5-um-aperture VCSEL performs the higher power and greater quantum efficiency, but provide the narrower 3-dB bandwidth and higher RIN level. The 5.5-um-aperture VCSEL with the higher 3-dB bandwidth of 25.2 GHz and RIN of -135 dBc/Hz can support the highest data rate up to 84 and 140 Gbit/s for PAM-4 and 16-QAM OFDM data under FEC criterion at BtB. After transmitting through 100-m OM5-MMF, the 80 and 120 Gbit/s data transmission can be successfully achieved for PAM-4 and 16-QAM OFDM carried by the 5.5-um-aperture VCSEL with the receiving power penalty of 3.24 and 3.1 dB.