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Optically synchronized fibre links using spectrally pure chip-scale lasers

Abstract

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.

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Acknowledgements

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.

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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.

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Correspondence to Daniel J. Blumenthal.

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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). https://doi.org/10.1038/s41566-021-00831-w

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