Photonic microwave generation in the X- and K-band using integrated soliton microcombs

An Author Correction to this article was published on 18 May 2020

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Microwave photonic technologies, which upshift the carrier into the optical domain, have facilitated the generation and processing of ultra-wideband electronic signals at vastly reduced fractional bandwidths. For microwave photonic applications such as radars, optical communications and low-noise microwave generation, optical frequency combs are useful building blocks. By virtue of soliton microcombs, frequency combs can now be built using CMOS-compatible photonic integrated circuits. Yet, currently developed integrated soliton microcombs all operate with repetition rates significantly beyond those that conventional electronics can detect, preventing their use in microwave photonics. Access to this regime is challenging due to the required ultra-low waveguide loss and large dimensions of the nanophotonic resonators. Here, we demonstrate soliton microcombs operating in two widely employed microwave bands, the X-band (~10 GHz, for radar) and the K-band (~20 GHz, for 5G). Driven by a low-noise fibre laser, these devices produce more than 300 frequency lines within the 3 dB bandwidth, and generate microwave signals featuring phase noise levels comparable to modern electronic microwave oscillators. Our results establish integrated microcombs as viable low-noise microwave generators. Furthermore, the low soliton repetition rates are critical for future dense wavelength-division multiplexing channel generation schemes and could significantly reduce the system complexity of soliton-based integrated frequency synthesizers and atomic clocks.

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Fig. 1: Principle of photonic microwave generation using integrated soliton microcombs and characteristics of the Si3N4 microresonators.
Fig. 2: Single solitons with microwave K- and X-band repetition rates.
Fig. 3: Phase noise characterization of the soliton repetition rate.
Fig. 4: Soliton injection-locking to an external microwave source.
Fig. 5: Comparison of compact photonics-based microwave generators.

Data availability

The data that support the plots within this paper and other findings of this study are available on Zenodo ( All other data used in this study are available from the corresponding author upon reasonable request.

Change history

  • 18 May 2020

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.


  1. 1.

    Hecht, J. The bandwidth bottleneck that is throttling the Internet. Nature 536, 139–142 (2016).

    ADS  Google Scholar 

  2. 2.

    Capmany, J. & Novak, D. Microwave photonics combines two worlds. Nat. Photon. 1, 319–330 (2007).

    ADS  Google Scholar 

  3. 3.

    Supradeepa, V. et al. Comb-based radiofrequency photonic filters with rapid tunability and high selectivity. Nat. Photon. 6, 186–194 (2012).

    ADS  Google Scholar 

  4. 4.

    Ghelfi, P. et al. A fully photonics-based coherent radar system. Nature 507, 341–345 (2014).

    ADS  Google Scholar 

  5. 5.

    Khilo, A. et al. Photonic ADC: overcoming the bottleneck of electronic jitter. Opt. Express 20, 4454–4469 (2012).

    ADS  Google Scholar 

  6. 6.

    Lim, C. et al. Fiber-wireless networks and subsystem technologies. J. Lightw. Technol. 28, 390–405 (2010).

    ADS  Google Scholar 

  7. 7.

    Khan, M. H. et al. Ultrabroad-bandwidth arbitrary radiofrequency waveform generation with a silicon photonic chip-based spectral shaper. Nat. Photon. 4, 117–122 (2010).

    ADS  Google Scholar 

  8. 8.

    Ataie, V., Esman, D., Kuo, B.-P., Alic, N. & Radic, S. Subnoise detection of a fast random event. Science 350, 1343–1346 (2015).

    ADS  MathSciNet  MATH  Google Scholar 

  9. 9.

    Temprana, E. et al. Overcoming Kerr-induced capacity limit in optical fiber transmission. Science 348, 1445–1448 (2015).

    ADS  Google Scholar 

  10. 10.

    Riehle, F. Optical clock networks. Nat. Photon. 11, 25–31 (2017).

    ADS  Google Scholar 

  11. 11.

    Rappaport, T. S., Murdock, J. N. & Gutierrez, F. State of the art in 60-GHz integrated circuits and systems for wireless communications. Proc. IEEE 99, 1390–1436 (2011).

    Google Scholar 

  12. 12.

    Xie, X. et al. Photonic microwave signals with zeptosecond-level absolute timing noise. Nat. Photon. 11, 44–47 (2016).

    ADS  Google Scholar 

  13. 13.

    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).

    ADS  Google Scholar 

  14. 14.

    Liang, W. et al. High spectral purity Kerr frequency comb radio frequency photonic oscillator. Nat. Commun. 6, 8957 (2015).

    ADS  Google Scholar 

  15. 15.

    Marpaung, D., Yao, J. & Capmany, J. Integrated microwave photonics. Nat. Photon. 13, 80–90 (2019).

    ADS  Google Scholar 

  16. 16.

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

    Google Scholar 

  17. 17.

    Gaeta, A. L., Lipson, M. & Kippenberg, T. J. Photonic-chip-based frequency combs. Nat. Photon. 13, 158–169 (2019).

    ADS  Google Scholar 

  18. 18.

    Torres-Company, V. & Weiner, A. M. Optical frequency comb technology for ultra-broadband radio-frequency photonics. Laser Photon. Rev. 8, 368–393 (2014).

    ADS  Google Scholar 

  19. 19.

    Wu, J. et al. RF photonics: an optical microcombs’ perspective. IEEE J. Sel. Top. Quantum Electron. 24, 1–20 (2018).

    ADS  Google Scholar 

  20. 20.

    Xu, X. et al. Broadband microwave frequency conversion based on an integrated optical micro-comb source. J. Lightw. Technol. 38, 332–338 (2019).

    ADS  Google Scholar 

  21. 21.

    Moss, D. J., Morandotti, R., Gaeta, A. L. & Lipson, M. New CMOS-compatible platforms based on silicon nitride and Hydex for nonlinear optics. Nat. Photon. 7, 597–607 (2013).

    ADS  Google Scholar 

  22. 22.

    Gyger, F. et al. Observation of stimulated Brillouin scattering in silicon nitride integrated waveguides. Phys. Rev. Lett. 124, 013902 (2020).

    ADS  Google Scholar 

  23. 23.

    Herr, T. et al. Temporal solitons in optical microresonators. Nat. Photon. 8, 145–152 (2014).

    ADS  Google Scholar 

  24. 24.

    Leo, F. et al. Temporal cavity solitons in one-dimensional Kerr media as bits in an all-optical buffer. Nat. Photon. 4, 471–476 (2010).

    ADS  Google Scholar 

  25. 25.

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

    ADS  Google Scholar 

  26. 26.

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

    ADS  Google Scholar 

  27. 27.

    Joshi, C. et al. Thermally controlled comb generation and soliton modelocking in microresonators. Opt. Lett. 41, 2565–2568 (2016).

    ADS  Google Scholar 

  28. 28.

    Tian, H. et al. Hybrid integrated photonics using bulk acoustic resonators. Preprint at (2019).

  29. 29.

    Yang, K. Y. et al. Bridging ultrahigh-Q devices and photonic circuits. Nat. Photon. 12, 297–302 (2018).

    ADS  Google Scholar 

  30. 30.

    Johnson, A. R. et al. Chip-based frequency combs with sub-100 GHz repetition rates. Opt. Lett. 37, 875–877 (2012).

    ADS  Google Scholar 

  31. 31.

    Xuan, Y. et al. High-Q silicon nitride microresonators exhibiting low-power frequency comb initiation. Optica 3, 1171–1180 (2016).

    ADS  Google Scholar 

  32. 32.

    Li, Q. et al. Stably accessing octave-spanning microresonator frequency combs in the soliton regime. Optica 4, 193–203 (2017).

    ADS  Google Scholar 

  33. 33.

    Stone, J. R. et al. Thermal and nonlinear dissipative-soliton dynamics in Kerr-microresonator frequency combs. Phys. Rev. Lett. 121, 063902 (2018).

    ADS  Google Scholar 

  34. 34.

    Pfeiffer, M. H. P. et al. Photonic Damascene process for integrated high-Q microresonator based nonlinear photonics. Optica 3, 20–25 (2016).

    ADS  Google Scholar 

  35. 35.

    Liu, J. et al. Ultralow-power chip-based soliton microcombs for photonic integration. Optica 5, 1347–1353 (2018).

    ADS  Google Scholar 

  36. 36.

    Guo, H. et al. Universal dynamics and deterministic switching of dissipative Kerr solitons in optical microresonators. Nat. Phys. 13, 94–102 (2016).

    Google Scholar 

  37. 37.

    Morton, P. A. & Morton, M. J. High-power, ultra-low noise hybrid lasers for microwave photonics and optical sensing. J. Lightw. Technol. 36, 5048–5057 (2018).

    ADS  Google Scholar 

  38. 38.

    Huang, D. et al. High-power sub-kHz linewidth lasers fully integrated on silicon. Optica 6, 745–752 (2019).

    ADS  Google Scholar 

  39. 39.

    Mazur, M. et al. Enabling high spectral efficiency coherent superchannel transmission with soliton microcombs. Preprint at (2018).

  40. 40.

    Raja, A. S. et al. Chip-based soliton microcomb module using a hybrid semiconductor laser. Opt. Express 28, 2714–2721 (2020).

    ADS  Google Scholar 

  41. 41.

    Nelson, C. W., Hati, A. & Howe, D. A. A collapse of the cross-spectral function in phase noise metrology. Rev. Sci. Instrum. 85, 024705 (2014).

    ADS  Google Scholar 

  42. 42.

    Huang, G. et al. Thermorefractive noise in silicon-nitride microresonators. Phys. Rev. A 99, 061801 (2019).

    ADS  Google Scholar 

  43. 43.

    Yi, X. et al. Single-mode dispersive waves and soliton microcomb dynamics. Nat. Commun. 8, 14869 (2017).

    ADS  Google Scholar 

  44. 44.

    Weng, W. et al. Spectral purification of microwave signals with disciplined dissipative Kerr solitons. Phys. Rev. Lett. 122, 013902 (2019).

    ADS  Google Scholar 

  45. 45.

    Spencer, D. T. et al. An optical-frequency synthesizer using integrated photonics. Nature 557, 81–85 (2018).

    ADS  Google Scholar 

  46. 46.

    Newman, Z. L. et al. Architecture for the photonic integration of an optical atomic clock. Optica 6, 680–685 (2019).

    ADS  Google Scholar 

  47. 47.

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

    ADS  Google Scholar 

  48. 48.

    Merklein, M. et al. Widely tunable, low phase noise microwave source based on a photonic chip. Opt. Lett. 41, 4633–4636 (2016).

    ADS  Google Scholar 

  49. 49.

    Do, P. T. et al. Wideband tunable microwave signal generation in a silicon-based optoelectronic oscillator. Preprint at (2019).

  50. 50.

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

    ADS  Google Scholar 

  51. 51.

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

    ADS  Google Scholar 

  52. 52.

    Rice, P. et al. A 10 GHz dielectric resonator oscillator using GaN technology. 2004 IEEE MTT-S International Microwave Symposium Digest 3, 1497–1500 (2004).

    Google Scholar 

  53. 53.

    Bauters, J. F. et al. Planar waveguides with less than 0.1 dB/m propagation loss fabricated with wafer bonding. Opt. Express 19, 24090–24101 (2011).

    ADS  Google Scholar 

  54. 54.

    Spencer, D. T., Bauters, J. F., Heck, M. J. R. & Bowers, J. E. Integrated waveguide coupled Si3N4 resonators in the ultrahigh-Q regime. Optica 1, 153–157 (2014).

    ADS  Google Scholar 

  55. 55.

    Karpov, M. et al. Raman self-frequency shift of dissipative Kerr solitons in an optical microresonator. Phys. Rev. Lett. 116, 103902 (2016).

    ADS  Google Scholar 

  56. 56.

    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).

    ADS  Google Scholar 

  57. 57.

    Pfeiffer, M. H. P., Liu, J., Geiselmann, M. & Kippenberg, T. J. Coupling ideality of integrated planar high-Q microresonators. Phys. Rev. Appl. 7, 024026 (2017).

    ADS  Google Scholar 

  58. 58.

    Liu, J. et al. Double inverse nanotapers for efficient light coupling to integrated photonic devices. Opt. Lett. 43, 3200–3203 (2018).

    ADS  Google Scholar 

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We thank N. J. Engelsen, G. Huang, W. Weng, M. A. Anderson and S. A. Bhave for discussions. This work was supported by contract no. FA9550-19-C-7001 (KECOMO) from the Defense Advanced Research Projects Agency (DARPA), Microsystems Technology Office (MTO), by the Air Force Office of Scientific Research, Air Force Materiel Command, USAF under award no. FA9550-15-1-0250, and by the Swiss National Science Foundation under grant no. 176563 (BRIDGE) and no. 165933. E.L. and M.K. acknowledge support from the European Space Technology Centre under ESA contract nos. 4000116145/16/NL/MH/GM and 4000118777/16/NL/GM, respectively. J.H. acknowledges support provided by H.-Y. Tam and the General Research Fund of the Hong Kong Government under project PolyU 152207/15E. H.G. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under Marie Sklodowska-Curie IF grant no. 709249. The Si3N4 microresonator samples were fabricated in the EPFL Center of MicroNanoTechnology (CMi).

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J.L. designed and fabricated the Si3N4 samples, with assistance from R.N.W. and H.G. Samples were characterized and analysed by J.L. and J.H. J.H., J.L., A.S.R. and M.K. performed the soliton generation experiment. E.L., A.S.R., J.R., J.L. and R.B. performed the phase noise measurements and the soliton injection-locking experiment. J.L., R.B., E.L. and T.J.K. wrote the manuscript, with input from the other authors. T.J.K. supervised the project.

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Correspondence to Tobias J. Kippenberg.

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Liu, J., Lucas, E., Raja, A.S. et al. Photonic microwave generation in the X- and K-band using integrated soliton microcombs. Nat. Photonics 14, 486–491 (2020).

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