Simple Precise Time Signal Delivery Over Fiber Link Scheme

Abstract

The capability of transferring time signal to remote locations with high stability and accuracy for synchronization is crucial for many important occasions, involving very long-baseline interferometry, coherent radio telescope arrays, modern particle accelerator, and the Deep Space Network. The widely used satellite methods of time and frequency transfer are unable to preserve the stability delivered by modern timekeeping sources. To meet these high stability requirements, optical fiber link has been used to transfer frequency and time reference, which however still suffers from mechanical perturbation and temperature variation along the link and degrades the phase stability at the remote end. Over the past decade, researchers mainly focused on the frequency dissemination, and the transfer stability is now sufficient for most frequency standards. However, the time signal transfer stability is far below frequency reference, which is typically at the nanosecond accuracy level. We propose and demonstrate a stable time signal delivery scheme over fiber link utilizing frequency stabilization technology. In the scheme, we utilizing the frequency reference to compensate the link-length variation, and the total transfer delay is kept constant. Precise time signal is regenerated at the remote end. The fiber link we used in this paper is 10-km, and the long-term fiber delay variation is more than 800 ps. We obtain a time deviation of 40 ps at 1-s and falling to 2.3 ps at 1,000-s averaging time for time transfer. The time delay resolution of scheme is 1 ps, and the compensation range is in direct proportion with the fiber length. The proposed scheme shows a potential ability to precisely transfer time signal and frequency reference simultaneously, which is very suitable for long range time and frequency transfer.