We demonstrate a simultaneous transmission of time-frequency and data over a 160-km urban business network in Shanghai. The signals are transmitted through a cascaded optical link consisting of 48 km and 32 km, which are connected by an optical relay. The metrological signals are inserted into the communication network using dense wavelength division multiplexing. The influence of the interference between different signals has been discussed. The experimental results demonstrate that the radio frequency (RF) instability can reach 2.1×10-14 at 1 s and 2.3×10-17 at 10,000 s, and the time interval transfer of one pulse per second (1 PPS) signal with less than 10 ps at 1 s is obtained. This work paves the way for the widespread dissemination of ultra-stable time and frequency signals over the communication networks.

Based on dense wavelength-division multiplexing technology, frequency transfer and time synchronization are simultaneously realized over a compensated cascaded fiber link of 430 km, which is a part of the Beijing–Shanghai optical fiber backbone network. The entire cascaded system consists of two stages with fiber links of 280 and 150 km, respectively. To keep high symmetry and low noise, specific bi-directional erbium-doped fiber amplifiers are used to compensate the large optical attenuation of each fiber link. When the compensation servo is active in every stage, the cascaded system achieves the stability of 1.94×10 13 at 1 s and 1.34×10 16 at 104 s, for frequency transfer. It is also verified that the actual results of the cascaded system are in good agreement with the theoretical ones calculated from error theory. Simultaneously, after calibration of each stage, time synchronization is also realized. The final accuracy of the whole system is within 94 ps.