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標題: | 直調850-nm垂直共振腔面射型雷射於高速資料中心之應用 Directly modulated 850-nm VCSEL for High-speed Data center Application |
作者: | Hsuan-Yun Kao 高選昀 |
指導教授: | 吳肇欣(Chao-Hsin Wu) |
共同指導教授: | 林恭如(Gong-Ru Lin) |
關鍵字: | 垂直共振腔面射型雷射,資料中心, VCSEL,Data center, |
出版年 : | 2017 |
學位: | 碩士 |
摘要: | 隨著行動裝置的普及,人們對於資料傳輸的需求日益增大。近年來,特別在雲端傳輸或4-K數位影音有爆炸性需求的成長。為了及時處理高流量的資料訊息交換,高速資料中心或超級電腦因而被建立。根據IEEE P802.3bs的規範,原先100 Gbit/s的規格已升級成400 Gbit/s,去滿足日益的傳輸容量需求。在本論文中,我們以垂直共振腔面射型雷射(VCSEL)作為光源,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)格式,做為實際資料中心傳輸系統的展示。
在PAM-4傳輸系統中,我們以三種不同線寬的VCSEL為傳輸光源來進行實驗。在三種VCSEL之中,線寬最大的VCSEL(又稱多模VCSEL)擁有11微米寬的氧化孔徑、最大的光強度及最小的3-dB條變頻寬,只能達成22 GBaud及14 GBaud之PAM-4傳輸於背對背(BtB)與100-m POFC OM4多模光纖。線寬大小次之的VCSEL(又稱少模VCSEL)擁有5微米寬的氧化孔徑及較大的光訊號強度,能夠提供最高的傳輸容量為52 Gbit/s於背對被傳輸中。然而,經過100-m POFC OM4多模光纖傳輸後,受到模間色散(modal dispersion)的影響,迫使傳輸容量降至32 Gbit/。對照之下,線寬最小的VCSEL(又稱單模VCSEL)擁有3微米寬的氧化孔徑,在100-m POFC OM4多模光纖傳輸時,由於不受到模間色散(modal dispersion)的影響,因能提供最大的傳輸容量為34 Gbit/s與最小的功率代償為1.4 dB. 為了近一步提升傳輸容量,我們挑選色散效應最小的單模VCSEL,去進行預失真(pre-emphasis) PAM-4的實驗。在背對背與100-m 的OM4多模光纖的傳輸中,過預失真PAM-4的技術,單模VCSEL可以達成高達64 Gbit/s的傳輸容量。當我們繼續提升傳輸距離至200公尺及300公尺時,低頻至高頻的補償機制會使PAM-4的調變振幅減小,進而使傳輸容量縮小為52與48 Gbit/s。 接下來,我們成功展示了以16-QAM OFDM為調變格式,多模、少模、單模於100-m POFC OM4多模光纖傳輸比較。與PAM-4有相近的結果,多模VCSEL僅能達成最小傳輸容量為88及64 Gbit/s於背對背及100-m POFC OM4多模光纖的傳輸。對照之下,少模/單模的VCSEL能夠達成96/92與80/80 Gbit/s的傳輸容量。值得注意的是,經過100-m POFC OM4多模光纖傳輸後,單模VCSEL具有較低的功率代償為1.77dB。為了更提升傳輸容量,我們將原本POFC OM4多模光纖替換為Corning 的OM4多模光纖,並優化VCSEL的操作條件後,少模VCSEL能夠提升傳輸容量至100及92 Gbit/s在背對背及100-m Corning OM4多模光纖傳輸後。此外,我們使用預補償(pre-leveling)16-QAM OFDM的格式,以單模VCSEL作為光源,進行了變溫和長期穩定的傳輸測試。由於熱效應的緣故,單模VCSEL雖具需要較嚴格的操作溫度條件,但在1.5小時之內能夠保有其傳輸性能於QAM-OFDM的系統中。經過操作條件的優化後,單模VCSEL最終能提供傳輸容量皆為96 Gbit/s,於背對背及100-m100-m Corning OM4多模光纖的條件。 To relieve explosively increased demand on data capacity from real-time media access between mobile devices and interconnection in supercomputers or data-centers, ultrahigh-speed optical interconnects is established. According to the IEEE P802.3bs standard, the currently available Ethernet frames have to upgrade its data rate from 100 to 400 Gbit/s to satisfy this drastically increased requirement. In this thesis, a transmission link based on vertical-cavity surface-emitting lasers (VCSELs) with the encoding 4-level pulse amplitude modulation (PAM-4) and quadrature amplitude modulation orthogonal frequency division multiplexing (QAM-OFDM) data is demonstrated for data center optical interconnect. For the PAM-4 transmission, the three VCSEL chips with different spectral linewidth and transverse mode number are used as the transmitter. The VCSEL chip with the largest spectral linewidth and oxide-confined aperture of 11 m (also called multi-mode, MM VCSEL) exhibits the smallest modulation bandwidth and highest optical power which only achieved 22 GBaud and 14 GBaud over back-to-back (BtB) and 100-m POFC OM4 MMF transmission. The VCSEL chip with the smaller spectral linewidth and oxide-confined aperture of 5 m (also called few-mode, FM VCSEL) is able to support the highest transmission capacity of 52 Gbit/s due to the strongest throughput. Nevertheless, the transmission capacity still reduces to 32 Gbit/s after 100-m POFC OM4 MMF transmission owing to the induced modal dispersion. In contrast, the VCSEL chip with the smallest spectral linewidth and oxide-confined aperture of 3 m (also called single-mode, SM VCSEL) possesses an ignorable modal dispersion property and achieves a highest data rate of 34 Gbit/s with the lowest power penalty of 1.4 dB after propagating 100-m POFC OM4 MMF. As a result, the SM VCSEL chip which suffers from the lowest dispersion is selected to carry out the pre-emphasis PAM-4 experiment for achieving the higher transmission capacity. With the assist the pre-emphasis technology, the SM VCSEL chip can support the data rate as high as 64 Gbit/s for both BtB and 100-m POFC OM4 MMF transmission. By continuously lengthen the transmission distance to 200 and 300 m, the low-to-high frequency energy transformation significantly reduce the signal amplitude to limit the transmission capacities to 52 and 48 Gbit/s, respectively. Next, a comparison of MM/FM/SM VCSEL chips for QAM-OFDM transmission over 100-m POFC OM4 MMF is demonstrated. Similar to result of PAM-4 transmission, MM VCSEL chip supports the lowest data capacity of 88 and 64 Gbit/s for BtB and 100-m POFC OM4 MMF propagation, respectively. The FM/SM VCSEL chip is able to carry 96/92 and 80/80 Gbit/s in the case of BtB and 100-m POFC OM4 MMF transmission, respectively. Noted that the SM VCSEL chip with the less dispersion exhibits the lowest power penalty of 1.77 dB after POFC OM4 MMF transmission. In order to enhance the data capacity, by replacing the Corning OM4 MMF for POFC OM4 MMF and optimizing the FM VCSEL chip operating condition, the FM can further achieve the 100 and 92 Gbit/s for BtB and 100-m Corning OM4 MMF propagation. Furthermore, the thermal-dependent and long-term stability transmission performance of SM VCSEL chip with encoding pre-leveled 16-QAM OFDM modulation is demonstrated. Owing to the heat accumulation, the SM VCSEL chip exhibits a strict dependence on the operating temperature but still achieved a stable operation for at least 1.5 hours for QAM-OFDM transmission link. By optimizing the operation condition, the transmission capacities as high as 96 Gbit/s are demonstrated for pre-leveled 16-QAM OFDM link after BtB and 100-m Corning OM4 MMF transmission. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/68118 |
DOI: | 10.6342/NTU201704156 |
全文授權: | 有償授權 |
顯示於系所單位: | 光電工程學研究所 |
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