Optical Frequency Comb Generation Using CMOS Compatible Cascaded Mach-Zehnder Modulators

Optical frequency combs (OFCs) play a key role in a variety of applications and have been implemented primarily using mode-locked lasers, Kerr resonators, and electro-optic (EO) modulation. EO modulation-based OFC generation may not yield as many comb lines nor span as broad a bandwidth as mode-locked lasers or Kerr resonators; however, it offers a high degree of tunability in central frequency and comb spacing. Integrated solutions are of interest as they significantly reduce device footprint and enable large scale system integration. In this paper, we demonstrate flexible on-chip OFC generation using two cascaded EO Mach-Zehnder modulators in silicon photonics. We demonstrate quasi-rectangular OFCs with 9 lines and a comb spacing of up to 10 GHz with an amplitude variation (comb flatness) within 6.5 dB. The corresponding time-domain waveforms have a good fit with sinc-shaped Nyquist pulses having a full-width at half maximum duration as short as 11.4 ps.