  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 days in total. The weighted mean
of the fractional frequency offset of the transferred optical frequency over
the complete data set is $(-1.1 \pm 0.4) \times 10^{-20}$. 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%.
