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

In this letter, an implementation of high-precision time transfer over an 1839-km field fiber loop back link between two provincial capitals of China, Xi'an and Taiyuan, is reported. Time transfer stability of 6.5 ps at an averaging time of 1 s and 4.6 ps at 40000 s were achieved. The uncertainty for the time transfer system was evaluated, showing a budget of 56.2 ps. These results represent a significant milestone in achieving high-precision time transfer over a field fiber link spanning thousands of kilometers, signifying a record-breaking achievement for the real-field time transfer both in stability and in distance, which paves the way for constructing the nationwide high-precision time service via fiber network.