Electro Optic Frequency Comb Generation Using Silicon Photonic Modulators

"Silicon photonics is the most promising candidate to achieve the high data transmission rates required for future telecommunications bandwidth demands, which require upgraded optical interconnects. Optical modulators, such as Mach-Zehnder modulators, are one of the most important sub-components in any optical communication system. Leveraging the complementary metal-oxide semiconductor (CMOS) fabrication processes, the integration of optical devices become more cost effective and energy efficient. Optical frequency comb has widespread applications in microwave photonics and optical communications as a multi-wavelength source for wavelength division multiplexing and orthogonal frequency division multiplexing systems. The most common approach to generate optical frequency comb is based on the use of optical modulators. On-chip optical frequency comb generation has great flexibility to tune the center frequency based on the frequency of the continuous wave laser, comb spacing, and the number of comb lines based on adjusting the RF signal frequency, power, and phase that is applied to the electro-optic modulator. The limitation of this technique lies in the high insertion loss, especially in cascaded modulators. In this thesis, we investigate two integrated cascaded electro-optic modulators in CMOS-compatible silicon-on-insulator for optical frequency comb generation. The first comprises cascaded push-pull traveling wave Mach-Zehnder modulators (MZM) while the second involves cascaded microring modulators (MRM). The 9 comb lines with a spacing up to 10 GHz and bandwidth of 90 GHz for the cascaded MZM, and 5 comb lines with a spacing up to 10 GHz and a bandwidth of 50 GHz for the cascaded MRM. The measured temporal waveforms corresponding to the generated quasi-rectangular combs match with the sinc-shaped Nyquist pulses which are well-known for its high spectral efficiency and have zero inter-symbol interference. Lastly, we summarize and compare the performance of both modulators"--