Figure 5. Phase noise of the 10 GHz RF signal generated by the wide Kerr frequency comb without (red line, (1)) and with (blue line, (2)) a narrow-band RF filter placed after the PD.

The measured noise at offset frequencies below 1 kHz and above 10 MHz are within 3 dB of the noise floor of the OEwaves microwave phase noise measurement system used. Curves (3) and (4) describe theoretically found fundamental thermorefractive⁵⁰ and quantum noise⁴⁶ of the oscillator, respectively. Sensitivity of our PNTS is described by curve (5). The inset shows Allan deviation of the RF signal. Spectrum of the Kerr frequency comb resembles the optical spectrum shown in inset of Fig. 3.