Figure 3

Offset and noise characteristics of the phase-locked 18 GHz comb.

(a), RF amplitude noise of the offset-free Kerr frequency comb. Inset: an example RF amplitude noise of the Kerr frequency comb showing multiple peaks due to the beating between different comb families. The comb is tuned to be offset-free by fine control of the pump wavelength. (b), RF spectra of the beat notes from three different filtered spectral regions of the comb (black curve: whole spectrum excluding the pump; blue curve: 1529 to 1538 nm; red curve: 1555 to 1564 nm). All three measurements show bandwidth-limited beat notes at 17.986 GHz, characteristic of a phase-locked comb. The pedestal below 500 kHz offset frequency comes from the local oscillator used for downmixing the 17.986 GHz beat note (Fig. 3). (c), Optical intensity autocorrelation of the phase-locked Kerr frequency comb. The trace has a contrast of ~2, characteristic of a comb without a clean circulating high-peak power pulse.