RF frequency transfer over an urban 86 km fibre has been demonstrated with a resolution of 2×10 -18 at one day measuring time using an optical compensator. This result is obtained with a reference carrier frequency of 1 GHz, and a rapid scrambling of the polarisation state of the input light in order to reduce the sensitivity to the polarisation mode dispersion in the fibre. The limitation due to the fibre chromatic dispersion associated with the laser frequency fluctuations is highlighted and analyzed. A preliminary test of an extended compensated link over 186 km using optical amplifiers gives a resolution below 10 -17 at 1 day.
We present in this article results on a new dissemination system of an ultrastable reference signal at 100 MHz on a standard fiber network. The 100 MHz signal is simply transferred by amplitude modulation of an optical carrier. Two different approaches for compensating the noise introduced by the link have been implemented. The limits of the two systems are analyzed and several solutions are suggested in order to improve the frequency stability and to further extend the distribution distance. Nevertheless, our system is a good tool for the best cold atom fountains comparison between laboratories, up to 100 km, with a relative frequency resolution of 10 −14 at 1 s integration time and 10 −17 for 1 day of measurement. The distribution system may be upgraded to fulfill the stringent distribution requirements for the future optical clocks.
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