Vernier microcombs for integrated optical atomic clocks

Nat. Photon. 19, 400-406 (2025) · DOI: 10.1038/s41566-025-01617-0

License: CC BY 4.0.

Abstract

Kerr microcombs have drawn substantial interest as mass-manufacturable, compact alternatives to bulk frequency combs. This could enable the deployment of many comb-reliant applications previously confined to laboratories. Particularly enticing is the prospect of microcombs performing optical frequency division in compact optical atomic clocks. Unfortunately, it is difficult to meet the self-referencing requirement of microcombs in these systems owing to the approximately terahertz repetition rates typically required for octave-spanning comb generation. In addition, it is challenging to spectrally engineer a microcomb system to align a comb mode with an atomic clock transition with a sufficient signal-to-noise ratio. Here we adopt a Vernier dual-microcomb scheme for optical frequency division of a stabilized ultranarrow-linewidth continuous-wave laser at 871 nm to an ~235 MHz output frequency. This scheme enables shifting an ultrahigh-frequency (~100 GHz) carrier-envelope offset beat down to frequencies where detection is possible and simultaneously placing a comb line close to the 871 nm laser—tuned so that, if frequency doubled, it would fall close to the clock transition in $^{171}$Yb$^+$. Our dual-comb system can potentially combine with an integrated ion trap towards future chip-scale optical atomic clocks.

Figures

14 panels with data across 3 figures. Each panel page shows the plot, its columns and its files; each data.csv begins with a header naming the paper, the panel, the source, the license and the provenance route.

Fig. 1

Illustrative figure, no extractable data. Shown in the paper PDF.

Fig. 2

• panel (a): Optical spectrum of the main comb, measured after pump suppression with a coarse wavelength-division multiplexing filter: Power (dBm) against Wavelength (nm). data.csv
• panel (b): Optical spectrum of the Vernier comb, measured after pump suppression with a coarse wavelength-division multiplexing filter: Power (dBm) against Wavelength (nm). data.csv
• panel (c): Optical spectra at 0.01 nm resolution, Power (dBm) against Wavelength (nm): the short-wavelength main comb line (Short dispersive wave) and the SFG comb lines at 1 $\mu$m, used for f-2f beat detection. data.csv
• panel (d): Optical spectra near 871 nm at 0.01 nm resolution, Power (dBm) against Wavelength (nm): the LO laser at 871.042 nm, the fiber comb, and the SFG lines generated by summing two lines from one comb and from two combs. data.csv

Fig. 3

• panel (a): Electrical spectrum analyser trace of the $f_{\mathrm{LO\text{-}FC}}$ beat, unlocked: RF power (dBm) against frequency offset from 452.7 MHz (MHz), at 3 kHz resolution bandwidth over a 2 MHz span. data.csv
• panel (b): Electrical spectrum analyser trace of the $f_{\mathrm{LO\text{-}FC}}$ beat, phase-locked: RF power (dBm) against frequency offset from 454 MHz (MHz), at 3 kHz resolution bandwidth over a 2 MHz span. data.csv
• panel (c): Electrical spectrum analyser trace of the divided $f_{\mathrm{xCEO}}$ beat, unlocked: RF power (dBm) against frequency offset from 1275.3 MHz (MHz), at 3 kHz resolution bandwidth over a 2 MHz span. data.csv
• panel (d): Electrical spectrum analyser trace of the divided $f_{\mathrm{xCEO}}$ beat, phase-locked: RF power (dBm) against frequency offset from 1274.1 MHz (MHz), at 3 kHz resolution bandwidth over a 2 MHz span. data.csv
• panel (e): Electrical spectrum analyser trace of the divided $f_{\mathrm{Vernier}}$ beat, unlocked: RF power (dBm) against frequency offset from 494.5 MHz (MHz), at 3 kHz resolution bandwidth over a 2 MHz span. data.csv
• panel (f): Electrical spectrum analyser trace of the divided $f_{\mathrm{Vernier}}$ beat, phase-locked: RF power (dBm) against frequency offset from 492.8 MHz (MHz), at 3 kHz resolution bandwidth over a 2 MHz span. data.csv
• panel (g): Fractional Allan deviation against $\tau$ (s), on log-log axes, of the repetition rates of the main comb ($f_{rep1}$) and the Vernier comb ($f_{rep2}$), the pump laser ($f_{pump}$) and the fiber comb reference. data.csv

Fig. 4

• panel (a): Fractional Allan deviation of the RF clock against $\tau$ (s), on log-log axes: initial clock, interferometric noise, fiber comb (the optical reference), noise-suppressed clock, and noise-suppressed clock - 1000s. Error bars on the fiber comb and noise-suppressed clock curves are the spread over repeated runs. data.csv
• panel (d): Frequency counter trace of the 871 nm laser: Relative frequency (Hz), relative to 344.176787 THz, against Time (s). The laser is free-running at first and locked at around 40 s. data.csv
• panel (e): Frequency counter trace of the RF clock with noise suppression, over the same run as panel (d): Relative frequency (Hz), relative to 235.070311 MHz, against Time (s). data.csv

Cite

Kaiyi Wu et al. (11 authors). Vernier microcombs for integrated optical atomic clocks. Nat. Photon. 19, 400-406 (2025). https://doi.org/10.1038/s41566-025-01617-0

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