Transfer of an optical frequency over an urban fiber link

We transferred the frequency of an ultra-stable laser over 172 km of urban fiber. The link is composed of two cascaded 43-km fibers connecting two laboratories, LNE-SYRTE and LPL in Paris area. By implementing a recirculation loop we extend the link length up to 172 km. The link is fed with a 1542-nm cavity stabilized fiber laser having a sub-Hz linewidth. The fiber-induced phase noise is measured and cancelled with an all-fiber-based interferometer using commercial off-the-shelf pigtailed telecommunication components. The compensated link shows an Allan deviation of a few 10-16 at 1 s and a few 10-19 at 10,000 seconds.