Fiber-Optic Joint Time and Frequency Transfer With Active Stabilization of the Propagation Delay

In this paper, we describe the extension of our fiber-optic frequency transfer system to the time transfer capability. In contrast to standard two-way transfer schemes which offer only comparisons of two distant clocks, our system displays distribution functionality, reproducing the time and frequency signals of the reference clock in the remote location. By using active compensation of the fiber delay fluctuations, we obtained a time deviation of 0.3 ps (for time transfer) and an Allan deviation of 1.2 × 10^-17 (for frequency transfer) at 10⁵-s averaging. The experiments presented were carried out using a 60-km-long fiber loop, forming a part of the real urban network around Kraków.