Microwave Frequency Dissemination over a 212 km Cascaded Urban Fiber Link with Stability at the 10−18 Level

Abstract

To synchronize standard frequency signals between long-distance laboratories, we carried out a frequency dissemination experiment over a 212 km cascaded urban fiber link. This cascaded link was composed of two 106 km fiber links, in which the fiber noise was compensated by two microwave frequency dissemination systems. The two adjacent frequency dissemination systems used different frequency transmitted signals, preventing the influence of signal crosstalk between the received signal of the previous stage and the transmitted signal of the second stage caused by microwave signal leakage. The frequency dissemination over the cascaded link showed a dissemination fractional frequency instability of 6.2 × 10−15 at 1 s and 6.4 × 10−18 at 40,000 s, which is better than the transfer stability over the same 212 km single-stage link.