Combining fiber Brillouin amplification with a repeater laser station for fiber-based optical frequency dissemination over 1400km

We investigate optical frequency dissemination over a 1400 km long fiber link in looped configuration over a pair of underground fibers between Braunschweig and Strasbourg. This fiber link is the first to combine fiber Brillouin amplifiers with a repeater laser station. Phase-coherent operation over more than five days is demonstrated. We analyze the repeatability of the performance over four campaigns and present results of 65 d in total. The weighted mean of the fractional frequency offset of the transferred optical frequency over the complete data set is (-1.1 +/- 0.4) x 10(-20). By analyzing the stabilization signals of the two individual fibers, the correlation of the phase noise on the two fibers is shown to be > 98%.