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

Dedicated fiber links become the most precise and desirable means of transferring optical frequency at distances up to a few thousand kilometers. However, the need of installing special equipment along the link, and usually renting fibers exclusively for this use, cause that this preferable solution is cumbersome and expensive, and so accessible in severely limited range. In this paper we propose a method which improves the frequency transfer quality when only a standard (i.e., not modified for this purpose) DWDM optical telecommunication network is available. The proposed solution is based on the correlation identified between the 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 transfer accuracy by means of data post-processing. As we demonstrated, using the proposed method the frequency comparison uncertainty can be reduced to below 1 × 10 −16 for links up to 1500 km long.