Analysis of Sagnac Correction for Time Transfer in Optical Fibers

Abstract

Over the past few years, atomic clocks have been improving and are now reaching stabilities and accuracies of a few parts in 1018 in fractional frequency. Fiber-based time and frequency transfer techniques have demonstrated excellent performance in the comparison of state-of-art optical atomic clocks over thousands of kilometers. For highly accurate time and frequency transfers, relativistic effects which affect the signal propagation in optical fibers, need to be taken into account. The most important is the Sagnac correction because of the computation complexity and also the non-reciprocity in the two-way time transfer. Sagnac correction is an important source of uncertainty in fiber-based time and frequency transfer. Besides, not all important parameters are known with sufficient precision when we compute the Sagnac correction such as the large position error of fiber nodes and also the sparse fiber nodes. It is necessary to evaluate the Sagnac correction due to imperfect knowledge of parameters. In our work, several simulation fiber links in China are analyzed as specific examples to evaluate the influences of imperfect knowledge on the accuracy of the time transfer. The results show that in order to ensure one picosecond precision of time transfer using optical fiber, position accuracy of nodes should be higher than 500 m when the information of enough number of nodes can be obtained.