Long-distance frequency dissemination with a resolution of 10(-17)

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 CO 2 / OsO 4 frequency standard that stabilizes a femtosecond laser frequency comb. This demonstrates a resolution of 3 × 10 − 14 at 1 s. An upper value of the instability introduced by the femtosecond laser-based synthesizer is estimated as 1 × 10 − 14 at 1 s.