Figure 5: Detuning measurements.

(a) Measured detunings at the beginning of the comb generation process, with only the first pair of hyper-parametric sidebands being generated. The bottom graph shows the optical spectrum at different pump powers. Threshold for comb generation is reached at higher detunings for higher pump powers. The generated comb sidebands are generated close to zero detuning at a spacing determined by the resonator dispersion (curvature of the broad grey line in the background for comparison). (b) Detuning measurements for three different phase-locked comb states in a hot resonator. The curvature of the detuning follows the microresonator dispersion (broad grey line in the background), without obvious shifts due to self- and cross-phase modulation between comb modes. Remarkably, all the comb modes, including the pump laser are red-detuned in the comb states in the two lower spectra (green triangles and blue circles in the detuning plot).