Progress on an optical link for ultra-stable frequency dissemination using a public telecommunication network

We transfer the frequency of an ultra-stable laser over a 470-km optical link comprising 400 km of public telecommunication fiber network, simultaneously carrying data traffic. A dense wavelength division multiplexing scheme is used. The ultrastable signal is inserted in and extracted from the communication network using bidirectional optical add-drop multiplexers. The link passes through two important nodes of the telecommunication network and an amplification stage. The phase noise on the optical link is compensated with the usual round-trip technique. The 470-km multiplexed link shows an Allan deviation of 5×10^-15 at one second and 1.3×10^-18 after 1 hour. This work paves the way to a wide dissemination of ultra stable optical clock signals between distant laboratories via the Internet network.