Remote synchronization of atomic clocks

In the paper we present and briefly characterize the methods of remote synchronization of atomic clocks. Two groups of technical solution are presented, namely the methods employing satellites, especially GPS Common View and Two Way Satelite Time and Frequency Transfer and the group of systems, which employs the ground-base fiber optic networks. The unidirectional and bidirectional time/frequency transfer schemes are considered, and theirs main limitations are pointed out. Finally, the newly established atomic clock signals distribution network called Optime is presented. In a first step, the network was a simple link which primary objective was to connect two most important Time and Frequency laboratories in Poland - in Central Office of Measures (GUM, Warsaw) and in Astrogeodynamic Observatory (AOS) in Borowiec near Poznan. Recently, Optime has been expanded by adding three newly installed branches connecting GUM and Orange Synchronization Center and AOS with National Laboratory of Atomic, Molecular and Optical Physics in Torun. and Astronomic Center in Piwnice.