Evaluation of Time Transfer Units for Time and Frequency Transfer in Optical Fibers Utilizing a Passive Technique Based on SONET/SDH

The time transfer method of using passive listening and detection of SDH frame headers in fiberoptical networks has been presented earlier. Previous results, using commercialized equipment and commercial fiber-links, have shown that time transfer with a precision of the order of a few nanoseconds is possible over links with network distances exceeding 1100 km. The motivation of the work has been to develop an alternative and complementary time transfer method using existing infrastructure and to make it accessible to regular users of time keeping equipment. All previous reported experimental results were performed by SP Technical Research Institute of Sweden in commercial data communication networks in Sweden and Finland. This paper will report on the recent results from an experimental fiber test network implemented at the U.S. Naval Observatory. The fiber network is in a loop-back configuration with the two node elements in the same rack. The fiber link that connects the nodes is in an environmental chamber that allows a means to apply controlled fiber length fluctuations to the link. The performance of the Time Transfer Unit (TTU) was evaluated in this setting. This will be the first independent evaluation of the TTU equipment.