| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 107 === 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.
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