Improving Accuracy of Optical Frequency Transfer over Non-Modified DWDM Optical Networks

Dedicated fiber links become the more precise and desirable mean for comparing optical clocks and for optical frequency transfer at distances up to a few thousands kilometers. The need of installing special equipment along the link, and usually renting fibers exclusively for frequency transfer, cause that this preferable solution is cumbersome and expensive, and so accessible in severely limited range. In this paper we propose an improved method for comparing optical clocks with use of standard (i.e. not modified for this purpose) DWDM optical telecommunication network. The proposed solution is based on identified correlation between residual phase noise present in a DWDM-based optical frequency transfer and the in-loop phase correcting signal, which can be easily registered and used for improving the comparison accuracy by means of data postprocessing. As we demonstrated, using the proposed method the clocks comparison, uncertainty may be reduced to well below 1×10^-16 for link length in range of 1500 km.