The rapid growth in the amount of data being transferred within data centres, combined with the slowdown in Moore’s Law, creates challenges for the future scalability of electronically switched data-centre networks. Optical switches could offer a future-proof alternative, and photonic integration platforms have been demonstrated with nanosecond-scale optical switching times. End-to-end switching time is, however, currently limited by the clock and data recovery time, which typically takes microseconds, removing the benefits of nanosecond optical switching. Here we show that a clock phase caching technique can provide clock and data recovery times of under 625 ps (16 symbols at 25.6 Gb s−1). Our approach uses the measurement and storage of clock phase values in a synchronized network to simplify clock and data recovery versus conventional asynchronous approaches. We demonstrate the capabilities of our technique using a real-time prototype with commercial transceivers and validate its resilience against temperature variation and clock jitter.
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We acknowledge financial support from Microsoft, Inphi Inc. and EPSRC grants EP/R041792/1 and EP/R035342/1 and Royal Society Paul Instrument Fund PIF/R1/180001. Eblana Photonics provided the lasers used in this work. We thank P. Watts for helpful discussion at the early stages of the work and E. Vonhof for assistance in the generation of the figures.
A patent application, entitled ‘Phase Caching for Fast Data Recovery’, has been filed by Microsoft Technology Licensing, LLC with the US Patent and Trademark Office on 27 October 2017, on the technology described in this Article. This patent is currently pending (patent no. US20190132112A1).
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B, Data centre traffic pattern; C, Impact of traffic on throughput.
A, 48 hour stability; B, Tolerance to rapid temperature change.
A, Impact of rate-of-change of temperature on clock phase caching; B, Minimum required phase update rate as a function of rate-of-change of temperature.
A, Impact of sinusoidal jitter on clock phase caching; B, Impact of Gaussian jitter on clock phase caching.
Clock phase caching scalability.
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Clark, K.A., Cletheroe, D., Gerard, T. et al. Synchronous subnanosecond clock and data recovery for optically switched data centres using clock phase caching. Nat Electron 3, 426–433 (2020). https://doi.org/10.1038/s41928-020-0423-y