Abstract
In order to meet the time service needs of high-precision, long-distance, and multinode optical network, this paper proposes a new time synchronization solution, which combines the wavelength division multiplexing (WDM) technology with cascaded taming clock technology. The WDM technology is used for time synchronization between each pair of master-slave nodes. In the system, there are two wavelengths on the fiber link between the master node and the slave node for transmitting signals. 1 plus per second (PPS) signal, time code signal, and 10 MHz signal are, respectively, and successively, sent to the optical fiber link. By solving the one-way delay through analysis of error contribution and link characteristics of the time transmission process, time synchronization of the master-slave nodes pair is achieved. Furthermore, the authors adopt cascaded taming clock technology to ensure accurate time synchronization of each node. A 700 km long-distance time-frequency synchronization system is constructed in the laboratory. The system uses a cesium atomic clock as the reference clock source and transmits the signals through 8 small rubidium atomic clocks (RB clocks) hierarchically. Results from the experiment show that the long-term time stability is 47.5 ps/104 s. The system’s structural characteristics and the experiment results meet the requirements to allow practical use of high-precision time synchronization in networks. This proposed solution can be applied in various civil, commercial, and military fields.
Highlights
Time is an essential fundamental physical quantity, which has become the physical quantity with the highest measurement accuracy among the seven international basic units [1,2,3]
The working temperature of the terminal equipment was controlled in a small fluctuation by air conditioning. e experimental steps and results are as follows: (1) 700 km optical fiber time-frequency synchronization system is connected step by step according to Figure 4
For buried or suspended optical fiber, the temperature change of -20°C to 40°C can cover the general situation. e temperature range of this experiment is -20°C to 40°C because the optical fiber disk is used instead of the optical fiber cable. e experimental steps are as follows: (1) 700 km optical fiber time-frequency synchronization system is connected step by step according to Figure 4, in which the optical fiber disk of the 600–650 km section is placed in the temperature box
Summary
Time is an essential fundamental physical quantity, which has become the physical quantity with the highest measurement accuracy among the seven international basic units [1,2,3]. Scientific research, navigation and positioning, aerospace, power transmission, military security, and other fields are continually improving the demand for time synchronization accuracy and stability [9, 10]. Sliwczynski et al adopted the round-trip method to achieve a synchronization accuracy of 50 ps in the 615 km WDM optical fiber time synchronization experiment in 2015 [18]. Wu Guiling et al adopted the BTDM scheme in the 2000 km optical fiber experiment, which achieved a time transfer stability of 23 ps/105 s and a time synchronization accuracy of 30 ps [19, 20]. All the above researches have achieved excellent transmission accuracy and stability Most of these schemes used point-to-point time transmission in longdistance optical signal transmission, in which the optical amplifier was used to extend the transmission length. Commercial optical cables have been laid along highways and railways between these cities. erefore, this scheme is extremely suitable for the realization of high-precision timefrequency synchronization between cities and meets the needs of time synchronization practicality and networking in many fields
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