Long Haul Time and Frequency Distribution in Different DWDM Systems.

In this paper, we have presented the possibility of time and frequency (T&F) distribution in two generations of dense wavelength-division-multiplexing (DWDM) networks: the older one, equipped with dispersion compensation fiber (DCF) modules, and the newest, without in-line chromatic dispersion compensation (dedicated for coherent signals). The experiments were performed in a 1500-km loop arranged in the PIONIER production network, with T&F signals regarded as so-called "alien wavelength" network service. In the newest DWDM version, we observed very good stability of delivered signals: modified Allan deviation approach 10 for averaging longer than 10 s (for 10-MHz frequency signal), and time deviation below 15 ps for averaging up to 10 s for 1 PPS time signal. These results show that the DWDM alien wavelength service can be used for high-demanding applications like cesium fountains comparisons. Results achieved for the former version of DWDM were about one magnitude worse for a long-term comparison, but it can still be useful for less demanding applications. We found that the main reason for relatively poor results observed in the older generation of DWDM is the impact of the DCFs used in this DWDM approach.