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Unrepeated White Rabbit Time Synchronisation over a 300 km Optical Fibre Link

Ben Amies-King, Marco Lucamarini

Abstract

White Rabbit (WR) technology provides a commercially-available off-the-shelf solution for time synchronisation with sub-nanosecond accuracy and picosecond-level precision over optical fibre links typically spanning tens of kilometres. Such high-performance time dissemination can support a variety of applications, including position, navigation and timing (PNT), financial transactions, metrology, as well as entanglement and quantum key distribution (QKD). Demonstrations of WR over significantly longer distances remain few and far between, particularly in scenarios where intermediate amplification is unavailable, such as stretches of long-haul underwater fibre. In this work, we report the longest unrepeated deployment of WR to date, achieving time synchronisation over a 300 km (51.34 dB) single-span optical fibre link, even in highly asymmetrical configurations, with 99.86% uptime, whilst maintaining picosecond-level precision and sub-nanosecond accuracy. This was achieved through careful selection and optimisation of the components deployed at the link's end points. By leveraging standard telecom fibre and off-the-shelf hardware, our results pave the way for a scalable and standardised timing backbone for large-scale quantum networks, offering a practical route toward time distribution in future heterogeneous quantum communication systems.

Unrepeated White Rabbit Time Synchronisation over a 300 km Optical Fibre Link

Abstract

White Rabbit (WR) technology provides a commercially-available off-the-shelf solution for time synchronisation with sub-nanosecond accuracy and picosecond-level precision over optical fibre links typically spanning tens of kilometres. Such high-performance time dissemination can support a variety of applications, including position, navigation and timing (PNT), financial transactions, metrology, as well as entanglement and quantum key distribution (QKD). Demonstrations of WR over significantly longer distances remain few and far between, particularly in scenarios where intermediate amplification is unavailable, such as stretches of long-haul underwater fibre. In this work, we report the longest unrepeated deployment of WR to date, achieving time synchronisation over a 300 km (51.34 dB) single-span optical fibre link, even in highly asymmetrical configurations, with 99.86% uptime, whilst maintaining picosecond-level precision and sub-nanosecond accuracy. This was achieved through careful selection and optimisation of the components deployed at the link's end points. By leveraging standard telecom fibre and off-the-shelf hardware, our results pave the way for a scalable and standardised timing backbone for large-scale quantum networks, offering a practical route toward time distribution in future heterogeneous quantum communication systems.

Paper Structure

This paper contains 4 sections, 4 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Methods
  3. Results
  4. Discussion

Figures (2)

  • Figure 1: Schematic diagrams of the three White Rabbit (WR) configurations considered in this work, and associated characterisation. aAsymmetric: 300km duplex fibre (one arm of 300km and one of 100km) with one-way loss of 51.34dB for the 300km link. A single wavelength of 1547.72nm is used on both channels. bSymmetric: 150km duplex fibre, with a single wavelength. cTypical: WR over $L$ km simplex fibre, with two wavelengths corresponding to the two directions of propagation. d Characterisation of EDFA gain and noise spectrum for a 1550nm 1kHz linewidth laser input with optical power $P_L$. e A representation of the six 50km stretches comprising the 300km channel, with their measured lengths and respective average loss coefficients.
  • Figure 2: a Time deviation $\sigma_x (\tau)$ (Equation \ref{['eq:tdev']}) and b maximum time interval error $\textrm{MTIE}(\tau)$ (Equation \ref{['eq:mtie']}) of the the duplex 300km (black crosses), duplex 150km (red squares), simplex 150km (blue hexagons), and simplex 7km (green triangles) demonstrations.