Time and frequency transfer over a 500 km cascaded White Rabbit network

We perform experiments with White Rabbit for time and frequency dissemination over long distance optical fiber links. We consider a unidirectional link setup to ensure compatibility with active telecommunication networks and build the first four-span 500 km cascaded White Rabbit link, using commercial White Rabbit equipment and improved software parameters. We demonstrate a frequency transfer stability at the level of 2 × 10
⁻¹⁵
at 200 000 s of integration time. The time transfer stability reaches a minimum of 1.2 ps at 20 seconds of integration time. Finally, we compare our results with infield applications and discuss the limitations of the performance.