- 學位論文
矽及富碳碳化矽馬赫任德調變器
Si and C-rich SiC Based Mach-Zehnder Modulators
摘要
在這篇論文中，為了達到高速資料傳輸，因此分析了使用電光效應的矽基馬赫任德調變器(MZM)以及全光非線性克爾效應主導的富碳碳化矽微米環共振馬赫任德調變器(MZM)。其中，單一光路調變非對稱矽基馬赫任德調變器(MZM)證實了可以應用於資料傳輸中心的短距離與長距離傳輸，且使用的傳輸格式有不歸零開關鍵控調變(NRZ-OOK)與四階脈衝強度調變(PAM-4)，另外，使用半導體製程技術製作了富碳碳化矽微米環共振馬赫任德調變器，並進行模擬與分析，為了使用Fano共振特性增強非線性克爾調變來達到全光波長轉換與啁啾-色散補償。 在第二章，使用電光效應調變的單一光路調變非對稱矽基MZM 證實了使用訊 號預補償的PAM-4 訊號格式可達到單一通道100 Gbit/s 的位元率，2 毫米的相位調 變長度在載子排開的PN 接合結構下，展現的VπL 與消光比(ER)分別為0.909 V·cm 與12.7 dB，如此低的VπL 可以符合資料傳輸中心的規範(1.7 V·cm)，此外，入射 光經過單一光路調變非對稱矽基MZM 後，得到的平均功率與側模抑制比(SMSR) 分別為0 dBm 與58.28 dB，另外，在終端加上一個50 GHz 50 歐姆的終止器來達 到阻抗匹配，這使得單一光路調變非對稱矽基MZM 的-3 dB 頻寬可高達33 GHz， 為了減小色散造成的RF 功率衰減，因此使用色散位移光纖(DSF)取代標準單模光 纖(SMF)。為了使NRZ-OOK 訊號達到無差錯標準，單一光路調變非對稱矽基MZM 在背對背、2-km SMF 和10-km DSF 的傳輸下可以達到的最高位元率分別為53、 53、50 Gbit/s ，而且在50 Gbit/s 的位元率下，2-km SMF 和10-km DSF 的傳輸分 別可得到0.2 與0.25 dB 的功率損耗(power penalty)。為了更進一步提高傳輸性能， 使用PAM-4 訊號格式來有效解決有限頻寬的問題，在背對背、2-km SMF 和10-km DSF 的傳輸情況下，可提高傳輸速度至50/50/26 Gbaud (100/100/52 Gbit/s)的包位 元率，且達到前項錯誤更正碼標準， 50 Gbaud 的PAM-4 在2-km SMF 的傳輸下，其 功率損耗為0.32 dB，而在26 Gbaud 的PAM-4 傳輸比較下，2-km SMF 和10-km DSF 的功率損耗分別為0.26 dB 與0.64 dB，10-km DSF 傳輸之所以有較大的功率損耗是因 為有較大的傳輸損耗以及光纖核心層不匹配造成的額外損耗。 在第三章中，富碳碳化矽微米環共振MZM 證實可以使用增強的非線性克爾效應 達成全光調變25 Gbit/s 位元率的脈衝式歸零開關鍵控(PRZ-OOK)訊號，藉由調整[CH4]/([CH4]+[SiH4])的流量比達0.94，可以增強富碳碳化矽微米環共振MZM 的非線 性折射率高達2.5×10^-12 cm2/W，使得強幫浦光注入下，可得到0.12 奈米的穿透梳譜紅 位移，為了提高全光幫浦-探測波長轉換效率，使用微米環形共振腔與MZM 進行干涉 產生較銳利的Fano 共振譜型。此外，經過設計的富碳碳化矽微米環共振MZM 在C 與L 光波段擁有平坦的正群速度色散，且在波長為1550 奈米時，觀察到2973 ps2/km 的正群速度色散，這顯示這樣的元件有相當大的潛力可以作為分波多工處理器以 及作為訊號拓寬補償器使原本因負群速度色散或負啁啾元件拓寬的訊號達到補 償。分析經過富碳碳化矽微米環共振MZM 後，脈衝寬度為100/40/20 皮米光脈衝 後的啁啾值，可得到啁啾值由-5.6/-8/-10.4 GHz 壓縮到-1.7/-2.2/-2.5 GHz，並得到脈 衝寬度拓寬係數(To/Ti)為0.96/0.97/0.976，充分證實元件具有壓縮脈衝與啁啾-色散 補償的功能。在實際應用上，富含C-C 鍵結的高C/Si 比富碳碳化矽使得非線性克 爾效應可以增強，使得PRZ-OOK 訊號格式傳輸達到25 Gbit/s 位元率且通過互補 金屬氧化物半導體(CMOS)的邏輯運算需求，以上的結論得到富碳碳化矽微米環共 振MZM 可以作為多功能的原件，例如啁啾-色散補償、波長轉換，以及訊號格式 的轉換。
關鍵字
資料中心 ； 矽光子 ； 馬赫任德調變器(MZM) ； 不歸零開關鍵控調變 (NRZ-OOK) ； 四階脈衝強度調變(PAM-4) ； 全光訊號轉換器 ； 啁啾-色散補償器 ； 非線性克爾效應 ； 富碳碳化矽 ； 微米環形共振腔 ； 脈衝歸零開關鍵控調變 (PRZ-OOK)並列摘要
In this thesis, the silicon-based Mach-Zehnder modulator and the C-rich SiCx based micro-ring assisted Mach-Zehnder modulator were analyzed to achieve high-speed data transmission whatever utilizing the electro-optic effect or all-optical nonlinear Kerr effect. The single-arm driven asymmetric Si MZM demonstrates the high-speed data transmission for short- and long-reach data center applications with the non-return-to-zero on-off keying (NRZ-OOK) and 4-level pulse amplitude modulation (PAM-4). The C-rich SiCx micro-ring assisted MZM waveguide was simulated, fabricated and analyzed for achieving all-optical wavelength conversion and chirp-dispersion compensation based on Fano resonance-enhanced nonlinear Kerr switching. In chapter 2, a 1550-nm single-arm driven asymmetric silicon Mach-Zehnder modulator (MZM) based on electro-optic effect for single-channel 100-Gbit/s 4-level pulse amplitude modulation (PAM-4) data with waveform pre-emphasis is demonstrated. The 2-mm phase shifter under carrier depletion of pn junction structure exhibits low VπL product and high extinction ratio of 0.909 V·cm and 12.7 dB, respectively. Such a low VπL product satisfying the criterion of data center standard of 1.7 V·cm leads the device to perform high-speed data transmission. In addition, the optical light through single-arm driven asymmetric Si MZM offers an average power of 0 dBm and an excellent side mode suppression ratio of 58.28 dB. With impedance matching of 50-GHz 50-Ω terminator at the end port, the modulation bandwidth of single-arm driven asymmetric Si MZM can reach as high as 33 GHz. To minimize the chromatic dispersion induce RF fading, the dispersion-shift fiber (DSF) is utilized to replace the single-mode fiber (SMF). For non-return-to-zero on-off keying (NRZ-OOK) data to meet the error-free criterion, the single-arm driven asymmetric Si MZM supports the highest modulation capacities of 53/53/50 Gbit/s over BtB, 2-km SMF and 10-km DSF transmission, respectively, and the receiving power penalties at 50 Gbit/s can achieve 0.2 and 0.25 dB after 2-km SMF and 10-km DSF propagation, respectively. To further improve the transmission performance, the PAM-4 data is employed to effectively utilize the limited modulation bandwidth. The maximal transmission capacities of BtB, 2-km SMF and 10-km DSF to meet KP4-FEC criterion are improved to 50/50/26 Gbaud (100/100/52 Gbit/s) with qualified BER of 1.52×10^-4/1.96×10^-4/1.36×10^-4, and the received 50-Gbaud PAM-4 data link provides a power penalty of 0.32 dB over 2-km SMF transmission. For a fair comparison at 26 Gbaud, the received PAM-4 data reveals power penalties of 0.26 dB and 0.64 dB after 2-km SMF and 10-km DSF transmission, which suffers from the propagation loss and core mismatch induced coupling loss. In chapter 3, the C-rich SiCx micro-ring assisted Mach-Zehnder modulator (MZM) waveguide is demonstrated for all-optical cross-wavelength 25-Gbit/s pulsed return-to-zero on-off keying (PRZ-OOK) data conversion based on enhanced nonlinear Kerr switching. By adjusting the [CH4]/([CH4]+[SiH4]) fluence ratio to 0.94, the C-rich SiCx micro-ring assisted MZM waveguide enlarges its nonlinear refractive index up to 2.5×10-12 cm2/W at 1550 nm, which can induce a red shift of 0.12 nm on the transmittance notch under the intensive pump. To improve the conversion efficiency of all-optical pump-to-probe wavelength conversion, the micro-ring assisted MZM is employed for interfering the sharp lineshapes of Fano resonance. In addition, the designed C-rich SiCx micro-ring assisted MZM waveguide exhibits flat chromatic dispersion at C- and L-band wavelengths with a positive group velocity dispersion (β2) of 2973 ps2/km at 1550 nm, which is potential for applying on wavelength division multiplexer (WDM) and compensating the signal distortion induced by negative β2 or negative chirp components. By analyzing the frequency chirp of three optical pulses with pulsewidths of 100/40/20 ps before and after passing through the C-rich SiCx micro-ring assisted MZM waveguide, the suppression of frequency chirp from -5.6/-8/-10.4 GHz to -1.7/-2.2/-2.5 GHz is observed with its corresponding pulsewidth broadening factors (To/Ti) of 0.96/0.97/0.976. Under pump-to-probe wavelength conversion, the full width at half maximum of the modulated probe is suppressed from 47.3 ps to 42.08 ps and 41.55 ps at a wavelength around 1547.98 nm and 1558.28 nm due to the chirp-dispersion compensation of the C-rich SiCx micro-ring assisted MZM waveguide. In application, the dense C-C bonds content formed by high C/Si composition ratio contribute to an enhanced nonlinear Kerr switching, which enables the all-optical PRZ-OOK data format conversion and inversion at 25 Gbit/s and qualifies the criterion of the complementary metal-oxide-semiconductor logics. These results reveal that the C-rich SiCx assisted MZM waveguide can be versatile functionalities including the chirp-dispersion compensation, wavelength conversion, and data-format conversion/inversion.