Stability Limitations of Optical Frequency Transfer in Telecommunication DWDM Networks

This article investigates the fundamental limitations of optical frequency transfer stability related to cost-effective implementation of signal transmission in duplex, unidirectional optical paths offered by a standard dense wavelength division multiplexing (DWDM) network. We pointed out the effect of a significant mismatch of phase fluctuations observed in pairs of fibers even when located in a common cable. We also measured the thermal sensitivities of individual DWDM optical modules in the context of the effectiveness of the signal stabilization system. Finally, we present the real implementation of the coherent optical carrier transfer in the operational DWDM network, showing the overall impact of all individual effects. We demonstrated that it is possible to obtain the long-term stability (one day averaging) within the range from 2 ×10^-16 to 4 ×10^-16 and typical frequency offset at the level of few times 10^-16 in a 1500-km-long line by using the soil-deployed cables.