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Optically synchronized fibre links using spectrally pure chip-scale lasers


Precision optical-frequency and phase synchronization over fibre is critical for a variety of applications, from timekeeping to quantum optics. Such applications utilize ultra-coherent sources based on stabilized table-top laser systems. Chip-scale versions of these systems may dramatically broaden the application landscape by reducing the cost, size and power of such exquisite sources. Links based on the required narrow-linewidth integrated lasers, compact reference cavities and control methodologies have not yet been presented. Here, we demonstrate an optically synchronized link that achieves an ultralow residual phase error variance of 3 × 10−4 rad2 at the receiver, using chip-scale stabilized lasers with laser linewidth of ~30 Hz and instability below 2 × 10−13 at 50 ms. This performance is made possible with integrated Brillouin lasers, compact reference cavities and a novel low-bandwidth optical-frequency-stabilized phase-locked loop. These results demonstrate a path towards low-power, precision applications including distributed atomic clocks, quantum links, database synchronization and digital-signal-processor-free coherent fibre interconnects.

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Fig. 1: Optically synchronized precision fibre link.
Fig. 2: The CS-SBS laser.
Fig. 3: Laser carrier and heterodyne beat note linewidth and stability measurements.
Fig. 4: Precision link operation and performance.

Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request.


  1. 1.

    Ma, L.-S., Jungner, P., Ye, J. & Hall, J. L. Delivering the same optical frequency at two places: accurate cancellation of phase noise introduced by an optical fiber or other time-varying path. Opt. Lett. 19, 1777–1779 (1994).

    ADS  Article  Google Scholar 

  2. 2.

    Hall, J. L. & Zhu, M. in International School of Physics Enrico Fermi Course CXVII, Laser Manipulation of Atoms and Ions (eds Arimondo, E. et al.) 671–702 (North Holland, 1993).

  3. 3.

    Foreman, S. M. et al. Coherent optical phase transfer over a 32-km fiber with 1-s instability at 10−17. Phys. Rev. Lett. 99, 153601 (2007).

    ADS  Article  Google Scholar 

  4. 4.

    Calonico, D. et al. High-accuracy coherent optical frequency transfer over a doubled 642-km fiber link. Appl. Phys. B 117, 979–986 (2014).

    ADS  Article  Google Scholar 

  5. 5.

    Roberts, B. M. et al. Search for transient variations of the fine structure constant and dark matter using fiber-linked optical atomic clocks. New J. Phys. 22, 093010 (2020).

    ADS  Article  Google Scholar 

  6. 6.

    Clivati, C. et al. A coherent fiber link for very long baseline interferometry. IEEE Trans. Ultrason. Ferroelectr. Freq. Control 62, 1907–1912 (2015).

    Article  Google Scholar 

  7. 7.

    Grotti, J. et al. Geodesy and metrology with a transportable optical clock. Nat. Phys. 14, 437–441 (2018).

    Article  Google Scholar 

  8. 8.

    Lisdat, C. et al. A clock network for geodesy and fundamental science. Nat. Commun. 7, 12443 (2016).

    ADS  Article  Google Scholar 

  9. 9.

    Fujieda, M. et al. All-optical link for direct comparison of distant optical clocks. Opt. Express 19, 16498–16507 (2011).

    ADS  Article  Google Scholar 

  10. 10.

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

    ADS  Article  Google Scholar 

  11. 11.

    Nakazawa, M., Hirooka, T., Yoshida, M. & Kasai, K. in Optical Fiber Telecommunications 6th edn (eds Kaminow, I. P. et al.) 297–336 (Academic Press, 2013).

  12. 12.

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

    ADS  Article  Google Scholar 

  13. 13.

    Matei, D. G. et al. 1.5-μm lasers with sub-10-mHz linewidth. Phys. Rev. Lett. 118, 263202 (2017).

    ADS  Article  Google Scholar 

  14. 14.

    Pillai, B. S. G. et al. End-to-end energy modeling and analysis of long-haul coherent transmission systems. J. Lightw. Technol. 32, 3093–3111 (2014).

    ADS  Article  Google Scholar 

  15. 15.

    Crivelli, D. E. et al. Architecture of a single-chip 50-Gb/s DP-QPSK/BPSK transceiver with electronic dispersion compensation for coherent optical channels. IEEE Trans. Circuits Syst. Regul. Pap. 61, 1012–1025 (2014).

    Article  Google Scholar 

  16. 16.

    Laperle, C. & O’Sullivan, M. Advances in high-speed DACs, ADCs and DSP for optical coherent transceivers. J. Lightw. Technol. 32, 629–643 (2014).

    ADS  Article  Google Scholar 

  17. 17.

    Corbett, J. C. et al. Spanner: Google’s globally-distributed database. In OSDI (2012) 251–264 (USENIX Association, 2012).

  18. 18.

    Dierikx, E. F. et al. White rabbit precision time protocol on long-distance fiber links. IEEE Trans. Ultrason. Ferroelectr. Freq. Control 63, 945–952 (2016).

    Article  Google Scholar 

  19. 19.

    Schediwy, S. W., Gozzard, D. R., Stobie, S., Malan, J. A. & Grainge, K. Stabilized microwave-frequency transfer using optical phase sensing and actuation. Opt. Lett. 42, 1648–1651 (2017).

    ADS  Article  Google Scholar 

  20. 20.

    Brodnik, G. M. et al. Chip-scale, optical-frequency-stabilized PLL for DSP-free, low-power coherent QAM in the DCI. In Optical Fiber Communication Conference (OFC) 2020 M3A.6 (OSA, 2020).

  21. 21.

    Blumenthal, D. J. et al. Frequency-stabilized links for coherent WDM fiber interconnects in the datacenter. J. Lightw. Technol. 38, 3376–3386 (2020).

    ADS  Article  Google Scholar 

  22. 22.

    Kikuchi, K. Fundamentals of coherent optical fiber communications. J. Lightw. Technol. 34, 157–179 (2016).

    ADS  Article  Google Scholar 

  23. 23.

    Perin, J. K., Shastri, A. & Kahn, J. M. Design of low-power DSP-free coherent receivers for data center links. J. Lightw. Technol. 35, 4650–4662 (2017).

    ADS  Article  Google Scholar 

  24. 24.

    Kazovsky, L. G. Balanced phase-locked loops for optical homodyne receivers: performance analysis, design considerations and laser linewidth requirements. J. Lightw. Technol. 4, 182–195 (1986).

    ADS  Article  Google Scholar 

  25. 25.

    Satyan, N. Phase noise reduction of a semiconductor laser in a composite optical phase-locked loop. Opt. Eng. 49, 124301 (2010).

    ADS  Article  Google Scholar 

  26. 26.

    Balakier, K., Ponnampalam, L., Fice, M. J., Renaud, C. C. & Seeds, A. J. Integrated semiconductor laser optical phase lock loops. IEEE J. Sel. Top. Quantum Electron. 24, 1–12 (2018).

    Article  Google Scholar 

  27. 27.

    Simsek, A. et al. Evolution of chip-scale heterodyne optical phase-locked loops toward Watt level power consumption. J. Lightw. Technol. 36, 258–264 (2018).

    ADS  Article  Google Scholar 

  28. 28.

    Park, H. et al. 40-Gbit/s coherent optical receiver using a Costas loop. Opt. Express 20, 9736–9741 (2012).

    ADS  Article  Google Scholar 

  29. 29.

    Drever, R. W. P. et al. Laser phase and frequency stabilization using an optical resonator. Appl. Phys. B Photophys. Laser Chem. 31, 97–105 (1983).

    ADS  Article  Google Scholar 

  30. 30.

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

    ADS  Article  Google Scholar 

  31. 31.

    Loh, W. et al. Dual-microcavity narrow-linewidth Brillouin laser. Optica 2, 225–232 (2015).

    ADS  Article  Google Scholar 

  32. 32.

    Lee, H. et al. Spiral resonators for on-chip laser frequency stabilization. Nat. Commun. 4, 2468 (2013).

    ADS  Article  Google Scholar 

  33. 33.

    Zhang, W. et al. Ultranarrow linewidth photonic-atomic laser. Laser Photon. Rev. 14, 1900293 (2020).

    ADS  Article  Google Scholar 

  34. 34.

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

    ADS  Article  Google Scholar 

  35. 35.

    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  Article  Google Scholar 

  36. 36.

    Debut, A., Randoux, S. & Zemmouri, J. Linewidth narrowing in Brillouin lasers: theoretical analysis. Phys. Rev. A 62, 023803 (2000).

    ADS  Article  Google Scholar 

  37. 37.

    Loh, W. et al. A microrod-resonator Brillouin laser with 240-Hz absolute linewidth. New J. Phys. 18, 045001 (2016).

    ADS  Article  Google Scholar 

  38. 38.

    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).

    ADS  MathSciNet  Article  Google Scholar 

  39. 39.

    Schilt, S. et al. Frequency discriminators for the characterization of narrow-spectrum heterodyne beat signals: application to the measurement of a sub-hertz carrier-envelope-offset beat in an optical frequency comb. Rev. Sci. Instrum. 82, 123116 (2011).

    ADS  Article  Google Scholar 

  40. 40.

    Di Domenico, G., Schilt, S. & Thomann, P. Simple approach to the relation between laser frequency noise and laser line shape. Appl. Opt. 49, 4801–4807 (2010).

    ADS  Article  Google Scholar 

  41. 41.

    Nazarathy, M., Sorin, W. V., Baney, D. M. & Newton, S. A. Spectral analysis of optical mixing measurements. J. Lightw. Technol. 7, 1083–1096 (1989).

    ADS  Article  Google Scholar 

  42. 42.

    Kazovsky, L. G. & Atlas, D. A. A 1,320-nm experimental optical phase-locked loop: performance investigation and PSK homodyne experiments at 140 Mb/s and 2 Gb/s. J. Lightw. Technol. 8, 1414–1425 (1990).

    ADS  Article  Google Scholar 

  43. 43.

    Sluyski, M. A., Gass, K. & Stauffer, D. R. Implementation Agreement 400ZR OI-400ZR-01.0 (Optical Internetworking Forum, 2020).

  44. 44.

    Ip, E., Lau, A. P. T., Barros, D. J. F. & Kahn, J. M. Coherent detection in optical fiber systems. Opt. Express 16, 753–791 (2008).

    ADS  Article  Google Scholar 

  45. 45.

    Duan, L. General treatment of the thermal noises in optical fibers. Phys. Rev. A 86, 023817 (2012).

    ADS  Article  Google Scholar 

  46. 46.

    Idjadi, M. H. & Aflatouni, F. Nanophotonic phase noise filter in silicon. Nat. Photon. 14, 234–239 (2020).

    ADS  Article  Google Scholar 

  47. 47.

    Blumenthal, D. J., Heideman, R., Geuzebroek, D., Leinse, A. & Roeloffzen, C. Silicon nitride in silicon photonics. Proc. IEEE 106, 2209–2231 (2018).

    Article  Google Scholar 

  48. 48.

    Komljenovic, T. et al. Photonic integrated circuits using heterogeneous integration on silicon. Proc. IEEE 106, 2246–2257 (2018).

    Article  Google Scholar 

  49. 49.

    Brodnik, G. M. et al. Ultra-narrow linewidth chip-scale heterogeneously integrated silicon/III–V tunable laser pumped Si/Si3N4 SBS laser. In Conference on Lasers and Electro-Optics, OSA Technical Digest STu3M.5 (Optical Society of America, 2020).

  50. 50.

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

    ADS  Article  Google Scholar 

  51. 51.

    Zhao, Q. et al. Low-loss low thermo-optic coefficient Ta2O5 on crystal quartz planar optical waveguides. APL Photonics 5, 116103 (2020).

    ADS  Article  Google Scholar 

  52. 52.

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

    ADS  Article  Google Scholar 

  53. 53.

    Harrington, M. W. et al. Kerr soliton microcomb pumped by an integrated SBS laser for ultra-low linewidth WDM sources. In Optical Fiber Communication Conference (OFC) 2020 T4G.6 (OSA, 2020);

  54. 54.

    Gardner, F. M. Phaselock Techniques 3rd edn (Wiley, 2005).

    Book  Google Scholar 

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This research was supported by the OPEN 2018 Advanced Research Projects Agency–Energy (ARPA-E), US Department of Energy, under award no. DE-AR0001042. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing official policies of ARPA-E or the US Government.

Author information




G.M.B., D.J.B. and S.B.P. prepared the manuscript. D.J.B. conceived the OFS-PLL approach. D.J.B., G.M.B., M.W.H. and S.B.P. conceived the implemented OFS-PLL architecture. P.A.M. contributed the narrow-linewidth integrated optical pump sources. D.B. fabricated the SiN integrated high-Q resonator SBS laser chip. W.Z., L.S. and S.B.P. contributed the optical cavity used in the SBS laser stabilization stage. G.M.B. and M.W.H. performed the experiments, including SBS generation, SBS stabilization to cavities and optical phase locking along with the associated noise and performance characterizations. J.H.D. and R.O.B. contributed simulations of laser noise, fibre noise and performance and identification of noise contributions from SBS and cavity stabilization physics theory. All authors contributed to analysing the simulated and experimental results. D.J.B. and S.B.P. supervised and led the scientific collaboration.

Corresponding author

Correspondence to Daniel J. Blumenthal.

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Supplementary Information, including six sections of discussion, five figures, one table and 16 references.

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Brodnik, G.M., Harrington, M.W., Dallyn, J.H. et al. Optically synchronized fibre links using spectrally pure chip-scale lasers. Nat. Photon. (2021).

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