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Microresonator-referenced soliton microcombs with zeptosecond-level timing noise

Nature Photonics volume 19, pages 630–636 (2025)Cite this article

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Abstract

Optical frequency division relies on optical frequency combs to translate ultrastable optical frequency references coherently to the microwave domain. This technology has enabled the synthesis of microwave signals with ultralow timing noise; however, the necessary instrumentation remains too bulky for practical applications. Recently, efforts have focused on leveraging microphotonic technologies to enhance system compactness. Here we develop an optical frequency division system using microresonator-based frequency references and comb generators. The soliton microcomb formed in an integrated Si3N4 microresonator is stabilized to two lasers referenced to an ultrahigh-quality-factor MgF2 microresonator. Photodetection of the soliton pulse train produces 25-GHz microwaves with an absolute phase noise of –141 dBc Hz–1 (546 zs Hz−1/2) at a 10-kHz offset frequency, which can be further referenced to an atomic clock for improved long-term stability. The synthesized microwave signals are evaluated as carrier waves in communication and radar applications, demonstrating enhanced fidelity and sensitivity against interference compared with those derived from electronic oscillators. Our work demonstrates unprecedented coherence in microphotonic microwave oscillators, providing key building blocks for next-generation timekeeping, navigation and satellite communication systems.

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Fig. 1: Conceptual illustration of microresonator-based OFD.
Fig. 2: Characterization of optical frequency references.
Fig. 3: OFD characterization.
Fig. 4: Anti-interference experiments.
Fig. 5: Comparison of microwaves synthesized using microphotonic microwave oscillators, scaled to 10 GHz.

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Data availability

The data that support the plots within this Article are available via figshare at https://doi.org/10.6084/m9.figshare.28517780. All other data used in this study are available from the corresponding author upon reasonable request. Source data are provided with this paper.

References

  1. Hecht, J. et al. The bandwidth bottleneck. Nature 536, 139–142 (2016).

    Article  ADS  Google Scholar 

  2. Betz, J. W. Engineering Satellite-based Navigation and Timing: Global Navigation Satellite Systems, Signals, and Receivers (John Wiley & Sons, 2015).

  3. Kodheli, O. et al. Satellite communications in the new space era: a survey and future challenges. IEEE Commun. Surv. Tutor. 23, 70–109 (2020).

    Article  Google Scholar 

  4. Schlüter, W. & Behrend, D. The international VLBI service for geodesy and astrometry (IVS): current capabilities and future prospects. J. Geod. 81, 379–387 (2007).

    Article  ADS  Google Scholar 

  5. Doviak, R. J. et al. Doppler Radar and Weather Observations (Courier Corporation, 2006).

  6. Huang, W., Liu, X. & Gill, E. W. Ocean wind and wave measurements using X-band marine radar: a comprehensive review. Remote Sens. 9, 1261 (2017).

    Article  ADS  Google Scholar 

  7. Ayhan, S. et al. Impact of frequency ramp nonlinearity, phase noise, and SNR on FMCW radar accuracy. IEEE Trans. Microw. Theory Tech. 64, 3290–3301 (2016).

    Article  ADS  Google Scholar 

  8. Maleki, L. The optoelectronic oscillator. Nat. Photon. 5, 728–730 (2011).

    Article  ADS  Google Scholar 

  9. Tang, J. et al. Integrated optoelectronic oscillator. Opt. Express 26, 12257–12265 (2018).

    Article  ADS  Google Scholar 

  10. Li, J., Lee, H. & Vahala, K. J. Microwave synthesizer using an on-chip Brillouin oscillator. Nat. Commun. 4, 2097 (2013).

    Article  ADS  Google Scholar 

  11. Gundavarapu, S. et al. Sub-hertz fundamental linewidth photonic integrated Brillouin laser. Nat. Photon. 13, 60–67 (2019).

    Article  ADS  Google Scholar 

  12. Kittlaus, E. A. et al. A low-noise photonic heterodyne synthesizer and its application to millimeter-wave radar. Nat. Commun. 12, 4397 (2021).

    Article  ADS  Google Scholar 

  13. Diddams, S. A., Vahala, K. & Udem, T. Optical frequency combs: coherently uniting the electromagnetic spectrum. Science 369, eaay3676 (2020).

    Article  Google Scholar 

  14. Yao, Y., Jiang, Y. & Ma, L. Optical frequency division. Natl Sci. Rev. 7, 1801–1802 (2020).

    Article  Google Scholar 

  15. Fortier, T. M. et al. Generation of ultrastable microwaves via optical frequency division. Nat. Photon. 5, 425–429 (2011).

    Article  ADS  Google Scholar 

  16. Li, J., Yi, X., Lee, H., Diddams, S. A. & Vahala, K. J. Electro-optical frequency division and stable microwave synthesis. Science 345, 309–313 (2014).

    Article  ADS  Google Scholar 

  17. Xie, X. et al. Photonic microwave signals with zeptosecond-level absolute timing noise. Nat. Photon. 11, 44–47 (2017).

    Article  ADS  Google Scholar 

  18. Nakamura, T. et al. Coherent optical clock down-conversion for microwave frequencies with 10−18 instability. Science 368, 889–892 (2020).

    Article  ADS  Google Scholar 

  19. Li, J. & Vahala, K. Small-sized, ultra-low phase noise photonic microwave oscillators at X-Ka bands. Optica 10, 33–34 (2023).

    Article  ADS  Google Scholar 

  20. Tetsumoto, T. et al. Optically referenced 300 GHz millimetre-wave oscillator. Nat. Photon. 15, 516–522 (2021).

    Article  ADS  Google Scholar 

  21. Diddams, S. et al. An optical clock based on a single trapped 199Hg+ ion. Science 293, 825–828 (2001).

    Article  ADS  Google Scholar 

  22. Kessler, T. et al. A sub-40-mHz-linewidth laser based on a silicon single-crystal optical cavity. Nat. Photon. 6, 687–692 (2012).

    Article  ADS  Google Scholar 

  23. Kudelin, I. et al. Photonic chip-based low-noise microwave oscillator. Nature 627, 534–539 (2024).

    Article  ADS  Google Scholar 

  24. Sun, S. et al. Integrated optical frequency division for microwave and mmwave generation. Nature 627, 540–545 (2024).

    Article  ADS  Google Scholar 

  25. Kippenberg, T. J., Gaeta, A. L., Lipson, M. & Gorodetsky, M. L. Dissipative Kerr solitons in optical microresonators. Science 361, eaan8083 (2018).

    Article  Google Scholar 

  26. Matsko, A. B., Savchenkov, A. A., Yu, N. & Maleki, L. Whispering-gallery-mode resonators as frequency references. I. Fundamental limitations. J. Opt. Soc. Am. B 24, 1324–1335 (2007).

    Article  ADS  MathSciNet  Google Scholar 

  27. Alnis, J. et al. Thermal-noise-limited crystalline whispering-gallery-mode resonator for laser stabilization. Phys. Rev. A 84, 011804 (2011).

    Article  ADS  Google Scholar 

  28. Liu, K. et al. 36 Hz integral linewidth laser based on a photonic integrated 4.0 m coil resonator. Optica 9, 770–775 (2022).

    Article  ADS  Google Scholar 

  29. Jin, W. et al. Hertz-linewidth semiconductor lasers using CMOS-ready ultra-high-Q microresonators. Nat. Photon. 15, 346–353 (2021).

    Article  ADS  Google Scholar 

  30. Lee, H. et al. Chemically etched ultrahigh-Q wedge-resonator on a silicon chip. Nat. Photon. 6, 369–373 (2012).

    Article  ADS  Google Scholar 

  31. Wang, C. Y. et al. Mid-infrared optical frequency combs at 2.5 µm based on crystalline microresonators. Nat. Commun. 4, 1345 (2013).

    Article  ADS  Google Scholar 

  32. Liang, W. et al. High spectral purity Kerr frequency comb radio frequency photonic oscillator. Nat. Commun. 6, 7957 (2015).

    Article  ADS  Google Scholar 

  33. Yao, L. et al. Soliton microwave oscillators using over-sized billion Q optical microresonators. Optica 9, 561–564 (2022).

    Article  ADS  Google Scholar 

  34. Puckett, M. W. et al. 422 million intrinsic quality factor planar integrated all-waveguide resonator with sub-MHz linewidth. Nat. Commun. 12, 934 (2021).

    Article  ADS  Google Scholar 

  35. Qu, Z. et al. Fabrication of an ultra-high quality MgF2 micro-resonator for a single soliton comb generation. Opt. Express 31, 3005–3016 (2023).

    Article  ADS  Google Scholar 

  36. Ye, Z. et al. Foundry manufacturing of tight-confinement, dispersion-engineered, ultralow-loss silicon nitride photonic integrated circuits. Photon. Res. 11, 558–568 (2023).

    Article  Google Scholar 

  37. Yi, X., Yang, Q.-F., Yang, K. Y. & Vahala, K. Theory and measurement of the soliton self-frequency shift and efficiency in optical microcavities. Opt. Lett. 41, 3419–3422 (2016).

    Article  ADS  Google Scholar 

  38. Jeong, D. et al. Ultralow jitter silica microcomb. Optica 7, 1108–1111 (2020).

    Article  ADS  Google Scholar 

  39. Lao, C. et al. Quantum decoherence of dark pulses in optical microresonators. Nat. Commun. 14, 1802 (2023).

    Article  Google Scholar 

  40. Carr, J. J. in The Technician’s EMI Handbook 163–195 (Newnes, 2000).

  41. Lucas, E. et al. Ultralow-noise photonic microwave synthesis using a soliton microcomb-based transfer oscillator. Nat. Commun. 11, 374 (2020).

    Article  ADS  Google Scholar 

  42. Helgason, O’. B. et al. Surpassing the nonlinear conversion efficiency of soliton microcombs. Nat. Photon. 17, 992–999 (2023).

  43. Yang, Q.-F., Hu, Y., Torres-Company, V. & Vahala, K. Efficient microresonator frequency combs. eLight 4, 18 (2024).

    Article  Google Scholar 

  44. Boes, A. et al. Lithium niobate photonics: unlocking the electromagnetic spectrum. Science 379, eabj4396 (2023).

    Article  ADS  Google Scholar 

  45. Wang, C. et al. Integrated lithium niobate electro-optic modulators operating at CMOS-compatible voltages. Nature 562, 101–104 (2018).

    Article  ADS  Google Scholar 

  46. Shao, L. et al. Integrated microwave acousto-optic frequency shifter on thin-film lithium niobate. Opt. Express 28, 23728–23738 (2020).

    Article  ADS  Google Scholar 

  47. Li, B. et al. Reaching fiber-laser coherence in integrated photonics. Opt. Lett. 46, 5201–5204 (2021).

    Article  ADS  Google Scholar 

  48. Stern, B., Ji, X., Okawachi, Y., Gaeta, A. L. & Lipson, M. Battery-operated integrated frequency comb generator. Nature 562, 401–405 (2018).

    Article  Google Scholar 

  49. Raja, A. S. et al. Electrically pumped photonic integrated soliton microcomb. Nat. Commun. 10, 680 (2019).

    Article  ADS  Google Scholar 

  50. Shen, B. et al. Integrated turnkey soliton microcombs. Nature 582, 365–369 (2020).

    Article  ADS  Google Scholar 

  51. Xiang, C. et al. Laser soliton microcombs heterogeneously integrated on silicon. Science 373, 99–103 (2021).

    Article  ADS  Google Scholar 

  52. Liu, Y. et al. A photonic integrated circuit-based erbiumdoped amplifier. Science 376, 1309–1313 (2022).

    Article  ADS  Google Scholar 

  53. Liu, G. et al. Low-loss prism-waveguide optical coupling for ultrahigh-Q low-index monolithic resonators. Optica 5, 219–226 (2018).

    Article  ADS  Google Scholar 

  54. Anderson, M. et al. Highly efficient coupling of crystalline microresonators to integrated photonic waveguides. Opt. Lett. 43, 2106–2109 (2018).

    Article  ADS  Google Scholar 

  55. Liang, W. et al. Ultralow noise miniature external cavity semiconductor laser. Nat. Commun. 6, 7371 (2015).

    Article  ADS  Google Scholar 

  56. Liu, J. et al. Photonic microwave generation in the X- and K-band using integrated soliton microcombs. Nat. Photon. 14, 486–491 (2020).

    Article  ADS  Google Scholar 

  57. Zhao, Y. et al. All-optical frequency division on-chip using a single laser. Nature 627, 546–552 (2024).

    Article  ADS  Google Scholar 

  58. Kondratiev, N. & Gorodetsky, M. Thermorefractive noise in whispering gallery mode microresonators: analytical results and numerical simulation. Phys. Lett. A 382, 2265–2268 (2018).

    Article  ADS  Google Scholar 

  59. Gordon, J. P. & Haus, H. A. Random walk of coherently amplified solitons in optical fiber transmission. Opt. Lett. 11, 665–667 (1986).

    Article  ADS  Google Scholar 

  60. Sun, S. et al. Microcavity Kerr optical frequency division with integrated silicon nitride photonics. Nat. Photon. https://doi.org/10.1038/s41566-025-01668-3 (2025).

  61. Ji, Q.-X. et al. Dispersive-wave-agile optical frequency division. Nat. Photon. https://doi.org/10.1038/s41566-025-01667-4 (2025).

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Acknowledgements

The Si3N4 chips used in this work were fabricated by Qaleido Photonics. The MgF2 microresonators used in this work were fabricated and packaged by Peking University Yangtze Delta Institute of Optoelectronics. The project is supported by the Beijing Natural Science Foundation (Z210004), National Natural Science Foundation of China (92150108, 12293050 and 62305006), Nantong Science and Technology Bureau (MS12022003), National Key R&D Plan of China (grant number 2021YFB2800601) and the High-performance Computing Platform of Peking University.

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Author notes

  1. These authors contributed equally: Xing Jin, Zhenyu Xie, Xiangpeng Zhang, Hanfei Hou.

Authors and Affiliations

  1. State Key Laboratory for Artificial Microstructure and Mesoscopic Physics and Frontiers Science Center for Nano-optoelectronics, School of Physics, Peking University, Beijing, China

    Xing Jin, Zhenyu Xie, Hanfei Hou, Bingyan Wu, Xuanyi Zhang, Qihuang Gong & Qi-Fan Yang

  2. State Key Laboratory of Advanced Optical Communications System and Networks, School of Electronics, Peking University, Beijing, China

    Xiangpeng Zhang & Lin Chang

  3. Peking University Yangtze Delta Institute of Optoelectronics, Nantong, China

    Fangxing Zhang, Qihuang Gong & Qi-Fan Yang

  4. Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, China

    Qihuang Gong & Qi-Fan Yang

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Contributions

Experiments were conceived and designed by X.J., Z.X., Xiangpeng Zhang, H.H. and Q-F.Y. Measurements and data analysis were performed by X.J., Z.X., Xiangpeng Zhang, H.H., B.W. and Q-F.Y. Numerical simulations of thermorefractive noise were performed by X.J., H.H. and Xuanyi Zhang. The MgF2 microresonator was designed and fabricated by Xuanyi Zhang and F.Z. All authors participated in preparing the paper.

Corresponding author

Correspondence to Qi-Fan Yang.

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Extended data

Extended Data Fig. 1 Durability tests of optical references.

(a), Transmission spectra of a mode recorded from a packaged MgF2 microresonator before (upper panel) and after 4 months of operation (lower panel). Intrinsic Q factors are extracted from Lorentzian fits. (b), Transmission spectra of a packaged MgF2 microresonator before and after vibration test (see Supplementary Movie). (c), Transmission spectra of two modes before and after the vibration test. Intrinsic and external Q factors are extracted from Lorentzian fits.

Extended Data Fig. 2 Setup of PDH locking and multi-frequency delayed self-heterodyne interferometer.

VCO: voltage-controlled oscillator; PM: phase modulator; AOFS: acousto-optic frequency shifters; PC: polarization controller; LO: local oscillator; BPF: optical bandpass filter; OSC: oscilloscope.

Extended Data Fig. 3 Experimental setup for OFD.

VCO: voltage-controlled oscillator; EDFA: erbium-doped fiber amplifier; NF: notch filter; Amp: electrical amplifier; LPF: electrical lowpass filter.

Extended Data Fig. 4 Experimental setup for characterization of phase noise and ADEV.

(a), Experimental setup for characterizing the phase noise and ADEV of the OFD-generated microwave signals. (b), Schematic diagram of ultralow-noise microwave generation based on 1P-OFD. The extra time delay caused by the delay fiber in each section is set sequentially to τ/2, τ/4, τ/8, τ/16, τ/32, τ/64, with τ=5 ns.

Extended Data Fig. 5 Experiments setup for anti-interference experiments.

(a), The two signal generators produce a strong interference signal and a weak information signal respectively. The two signals are combined and mixed with an LO, and then sent to an electrical signal analyzer (ESA). (b), A signal generator and an arbitrary waveform generator (AWG) produce a strong interference signal and a baud information signal for data transmission respectively. The two signals are coupled together, mixed with an LO, and then sent to a vector signal analyzer (VSA) to obtain the constellation diagrams. (c), The radar signal is amplified and transmitted into free space via an antenna. A second antenna receives the target echo, which is further amplified and down-mixed to lower frequencies using ultralow-noise microwaves generated through one-point OFD. An ESA records the electrical spectra. Down-mixing reduces the ESA’s measurement noise floor.

Extended Data Table 1 Comparision of thermo-optic and thermo-expansion coefficients of low-loss optical materials at room temperature
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Jin, X., Xie, Z., Zhang, X. et al. Microresonator-referenced soliton microcombs with zeptosecond-level timing noise. Nat. Photon. 19, 630–636 (2025). https://doi.org/10.1038/s41566-025-01669-2

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