Optical fibers in time and frequency transfer

In the paper we analyze the fundamental accuracy limits of the time/frequency transfer in fiber-optic transmission systems based on intensity modulation and direct detection (IM-DD) of the light signal. The unidirectional and bidirectional time/frequency transfer schemes are considered, and their main limitations are pointed out. In particular, the impact of the fiber backscattering and the temperature dependence of the chromatic dispersion are examined in the context of bidirectional transfer. Finally, experimental results are presented and related to the preceding considerations. The experiments performed with a 60 km long fiber demonstrate single-picosecond accuracy of the time transfer. Our measurements suggest that it should be possible to obtain better accuracy of time/frequency transfer than that reported in the literature for systems based on the IM-DD principle.