Fiber-Optic Frequency and Timing Transfer Over an Urban Optical Fiber Link

We have developed a fiber-optic frequency and timing transfer system. It has been installed to provide timing synchronization between NICT and a distant university site connected by a 58-km urban optical fiber link. The timing signal generated at the remote site is derived from a frequency source that is stabilized using the link, and it is synchronized by a transferred timing marker. A second, separate fiber link confirms a timing synchronization uncertainty of 5.7 ns and a 10-MHz frequency instability of less than $10^{-16}$ at $10^{5}$ s averaging time. We additionally demonstrate a timing marker delivery using a code-based signal, which combines nanosecond-level uncertainty with the simplicity and compactness suitable for a system that can be deployed for synchronization across numerous sites.