可補償Ｏ-波段數據傳輸光纖色散的自由載子相關啁啾矽波導馬赫任德調製器

Abstract

對於未來的數據中心內通信，矽光子和線性調頻和色散補償技術在光通信中將發揮重要作用。馬赫曾德調製器（MZM）是其中關鍵的電光調製器，而光纖補償色散技術較少在O-波段中被討論，我們利用MZM中的線性調頻特性和光纖的色散，此補償技術可以被用在未來的光纖傳輸應用中。 第二章從理論上分析了矽p-n接面的等離子色散效應、等離子吸收效應、變容特性以及信號啁啾公式，將矽馬赫-曾德調製器(MZM) 上的操作電壓歸納於啁啾信號公式。在調製 MZM 以測量線性調頻 α 參數之前，量測此MZM 的基本特性以便於優化傳輸，包括 35.8 GHz 的 3 dB 元件頻率響應、電/光折射率約為 6.4 和 4.5、傳輸功率與偏置電壓曲線（P-V 曲線），以及由於施加射頻信號而導致的P-V 曲線偏移。54 Gbit/s NRZ-OOK信號可以在telecom 錯碼率(BER)標準（< 10^-9）下進行調製，顯示出此元件在400GBASE IEEE標準下的傳輸能力。結合上面的方程，並在 MZM 上調製 100 ps 脈寬信號，然後通過傳統的線性調頻頻率分析儀測量線性調頻 α 參數。實驗獲得的chirp α參數的平均值為-0.24/-1.21（上升/下降時間）且和時間相關，這顯示chirp參數 C具有更高的時間階項。 第三章對矽p-n接面波導MZM中的線性調頻和色散補償進行了模擬和實驗。在模擬中，同時參考了第 2 章中的脈衝展寬方程和線性調頻 α 參數。模擬脈衝補償比表明，脈衝寬度越小和線性調頻參數的絕對值越大，會使補償效果越明顯。且模擬同時也顯示單模光纖 (SMF) 中 不同波長1270 nm 和 1350 nm 的正色散符號和負色散符號導致信號脈衝寬度壓縮和展寬。模擬中也考慮了矽波導色散，但2μm的色散相互作用長度相對短於單模光纖距離的公里量級，且模擬顯示矽波導提供補償的僅造成公分級的單模光纖長度差異。為了增強補償效果，通過更換最先進的任意波形發生器（AWG）且使用預補償(pre-emphasis)技術，對 MZM 上施加的電驅動信號進行了優化，將上升/下降時間縮短至 7.75/4.61 ps。由於O波段波長附近的色散值較小，加上10 ps短脈寬的簡單one-bit信號，在波長為1270 nm的1/2/4/10 km的光纖長度時，量測到下降時間以0.91/0.83/0.8/0.74的比例壓縮；而在波長為1350 nm處的1/2/4/10 km光纖長度時，下降時間以1.07/1.14/1.3/1.48擴張。根據下降時間變化計算出的信號訊雜比 (SNR)加上光纖本身的損耗，模擬出在 1270 nm波長1/2/10 km單模光纖長度，和SNR相對於背對背傳輸變化了0.068/ +0.163/ -1.834 dB。而在傳輸數據中心內光纖距離內的50 Gbaud16-QAM-DMT信號，1/2 km單模光纖傳輸長度信噪比性能比背靠背傳輸好0.05/0.13 dB。 證明了數據中心內部通信中矽 MZM 和 單模光纖上的線性調頻和色散補償的信號改善。

For future intra-data center communication, the silicon photonics and chirp and dispersion compensation technique take important role in optical communications. Mach-Zender modulator (MZM) are the key device for electro-optic modulator. Chirp and dispersion compensation is seldomly discussed in O-band, but with chirp characteristic from MZM and dispersion from fiber, the compensation could be use on future optical fiber transmission application. In chapter 2, by theoretically analyzing the plasma dispersion effect, plasma absorption effect, varicap characteristic in the silicon p-n junction depletion region, and the signal chirp equation, the chirp in silicon Mach-Zehnder modulator (MZM) could be summarized into equations with operating voltage on MZM. Before modulating the MZM for measuring the chirp α-parameter, the basic characteristic of this MZM, such as 35.8 GHz of 3-dB bandwidth, electrical/optical refractive index around 6.4 and 4.5, transmission power to bias voltage curve (P-V curve), and the P-V curve shift due to applied RF signal. The 54 Gbit/s NRZ-OOK signal could be modulated under telecom BER performance (< 10^-9), showed the ability of transmission under IEEE standard of 400GBASE. And the chirp α-parameter was then measured by the conventional chirp frequency analyzer, combing the equation above, and modulating a 100 ps pulsewidth signal on MZM. The chirp α-parameter experimentally obtained with the average value of -0.24/-1.21 (rise/fall time) and time-dependent characteristics, which led to higher time order in chirp C. In chapter 3, the chirp and dispersion compensation was simulated and experimentally achieved in silicon p-n junction waveguide MZM. In the simulation, the pulse broadening equation and the chirp α-parameter from chapter 2 also took into consideration. The simulated pulse compensation ratio showed the smaller pulsewidth and bigger the absolute value of chirp parameter led to much obvious compensation effect. And positive and negative dispersion sign in 1270 nm and 1350 nm wavelength in single mode fiber (SMF) led to compression and broadening in signal pulsewidth. The silicon waveguide dispersion also considered in simulation, but the dispersion interaction length of 2 m was relatively shorter than km scale of SMF distance. The simulation showed the attribution the silicon waveguide provided only made cm scale of SMF difference. In order to enhance the compensation effect, the electrical driving signal applied on MZM was optimized to shorter rise/fall time to 7.75/4.61 ps by changing to state-of-art arbitrary waveform generator (AWG) and using pre-emphasis technique. With the small dispersion value around O-band wavelength and simple one-bit signal of 10 ps short pulsewidth, the fall time compressed with the ratio of 0.91/0.83/0.8/0.74 for 1/2/4/10 km of SMF in 1270 nm, while the broadened ratio of 1.07/1.14/1.3/1.48 for 1/2/4/10 km of SMF in 1350 nm. The SNR improvement calculated from transition time was 0.068/0.163/-1.83 dB in 1270 nm (1/2/10 km). The intra-data center fiber distance 50 Gbaud16-QAM-DMT signal was transmitted, and the SNR performance was 0.05/0.13 dB better than back-to-back transmission. Proved the signal improvement of chirp and dispersion compensation on silicon MZM and SMF in intra-data center communication.