Frequency Dissemination with Less than 2 × 10^-18Fractional-Frequency Instability Over 120 km of a Commercial Fiber Infrastructure

This work presents frequency dissemination with fractional-frequency instability of 2× 10-18 at a 100-second interrogation time on a single-mode fiber communication infrastructure, the system consisted of a Michelson interferometer over 120 km of optical fiber connecting the Weizmann Institute of Science and Tel Aviv University. We used optical add-drop multiplexers to incorporate the Michelson interferometer into an active communication infrastructure and used it to detect the phase noise accumulated on the fiber channel. A phase-locked loop controlling an acoustic optic modulator was used to correct it. This facilitated distributing a phase-stable frequency at the remote station.