1. INTRODUCTION . As the second stability and day stability of the optical clock has reached the order of ${10}^{-16}$ and ${10}^{-18}$ , time has become the most accurate physical quantity among the seven international basic units [ 1 ]. Time synchronization between each client and high-precision clock source has become an essential demand in scientific research, navigation and positioning, aerospace, power transmission, military security, and other fields. Due to its unique advantag...