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. 2020 Jan 17;11:374. doi: 10.1038/s41467-019-14059-4

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© The Author(s) 2020

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 3 — a Absolute single-sideband (SSB) phase noise of the 14.09 GHz signal generated by optical-to-microwave division of the USL via the Kerr comb transfer oscillator (blue) and obtained directly from the Kerr comb repetition rate (green) for comparison. The sensitivity limit of the phase noise analyser (3000 cross correlations applied at 1 Hz) is indicated by the grey shaded area. The red line is the limit inferred from the optical phase noise of the USL⁷¹, assuming an ideal noiseless division. b Precise determination of the optimal division factor N corresponding to the zero crossing of the linear fit (solid line) of the measured relative frequency change of the generated RF signal for a small variation of the repetition rate (dots). c Comparison between the RF spectra of the Kerr comb repetition rate and the optical-to-microwave frequency division result. The resolution bandwidth (RBW) is 5 Hz. d RF spectrum of the frequency-divided output signal, the RBW is 100 mHz. The data was acquired with the IQ demodulation mode of the spectrum analyser.