Long-distance frequency transfer over an urban fiber link using optical phase stabilization

We transferred the frequency of an ultrastable laser over 86 km of urban fiber. The link is composed of two cascaded 43 km fibers connecting two laboratories, Laboratoire National de Metrologie et d'Essais-Systemes de Reference Temps-Espace (LNE-SYRTE) and Laboratoire de Physique des Lasers (LPL), in the Paris area. In an effort to realistically demonstrate a link of 172 km without using spooled fiber extensions, we implemented a recirculation loop to double the length of the urban fiber link. 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 one second and a few 10(-19) at 10,000 seconds. (C) 2008 Optical Society of America