Time transfer in a 1839 km telecommunication fiber link demonstrating a picosecond-scale stability

In this letter, a very recent implementation of high-precision time transfer over a 1839 km field fiber loop back link between two provincial capitals of China, Xi’an and Taiyuan, is reported. Under a long-term test lasting for more than 63 hours, the time transfer performances were evaluated. Time transfer stability of 6.5 ps at an averaging time of 1 s and 4.6 ps at 40000 s were achieved. Meanwhile, transfer stability of the 10 MHz frequency signal was also measured, with 4.5E-12/s and 1.9E-15/10000 s being achieved. The results are to our knowledge a record for the real-field test of the time transfer in thousands-kilometer-level fiber links. This work paves the solid way for constructing the high-precision time service via fiber network across China.