Combination of an Optical Clock and Hydrogen Masers for Accurate Time Scale Calculation

The frequency stability and uncertainty of the optical clock have reached a magnitude of ${10}^{-18}$, making it a promising candidate for the next generation of time and frequency standards, and it may be used to redefine the international unit “second”. The time scale serves as a benchmark for accurately and continuously marking the passage of time, being the foundation of high-precision time generation. The production of a time scale relies on the continuous and stable operation of atomic clocks; however, optical clocks, as laboratory prototype devices, generally cannot operate continuously, thus involving optical clocks in time scale calculation presents a challenging issue. The proposed application of the Vondrak-Cepek combined filtering algorithm for joint time scale calculations with an optical clock and hydrogen masers aims to address the challenges posed by the intermittent operation of an optical clock. Initially, the ALGOS algorithm is used on the time difference data of the hydrogen masers to calculate and obtain a continuous and stable hydrogen maser clock time scale. Subsequently, the Vondrak-Cepek combined filtering algorithm is used to integrate the hydrogen maser time scale with the optical clock data to acquire a combined time scale that involves optical clocks in the calculation. Finally, the experimental results prove that the Vondrak-Cepek combined filtering algorithm effectively improves the performance of the combined time scale of optical clocks and hydrogen masers, with the time deviation of this time scale reaching the sub-nanosecond magnitude when compared with Coordinated Universal Time (UTC).