We use a new technique to disseminate microwave reference signals along ordinary optical fiber. The fractional frequency resolution of a link of 86 km in length is 10(-17) for a one day integration time, a resolution higher than the stability of the best microwave or optical clocks. We use the link to compare the microwave reference and a CO2/OsO4 frequency standard that stabilizes a femtosecond laser frequency comb. This demonstrates a resolution of 3x10(-14) at 1 s. An upper value of the instability introduced by the femtosecond laser-based synthesizer is estimated as 1x10(-14) at 1 s.
Daussy, C., Lopez, O., Amy-Klein, A., Goncharov, A., Guinet, M., Chardonnet, C., ... Luiten, A. (2005). Long-Distance Frequency Dissemination with a Resolution of 10-17. Physical Review Letters, 94(20), 203904-1-203904-4. https://doi.org/10.1103/PhysRevLett.94.203904