Fig. 2: Comb generation and fundamental characteristics.

a, Optical image of the InP DFB laser chip and the AlGaAsOI microresonators for dark-pulse generation. b, Normalized comb power when tuning the pump frequency across the resonance at around 1,552 nm. With 10-mW pump power, a dark-pulse Kerr comb could be accessed in a large frequency window (tens of gigahertz). CW, continuous wave. c, d, Two-FSR dark-pulse spectra (top) and the ‘turnkey’ behaviours (bottom) pumped by a commercial external laser (c) or a DFB laser chip (d) with an equal on chip power of 10 mW. A pair of flat wings besides the pump is formed in both spectra, exhibiting typical profile of the coherent dark-pulse microcombs. Inset: comb intensity noise (resolution BW of 100 kHz). The intensity noise of the dark-pulse Kerr comb is at the same power level as the electrical spectrum analyser background. P, power; f, frequency; PZT, lead zirconate titanate. e, Long-term stability of a free-running comb. f–k, Optical images and main performance of several Si-based fundamental devices, including a depletion-mode Si MZM (f), a TiN microheater (g), a Si spiral waveguide delay line (h), a vertical epitaxial Ge PD (i), a microring filter (j) and a CMOS driver for MZMs (k). More details can be found in Methods.