This paper presents a combined theoretical and experimental method for noise suppression in the repetition frequency (f_r) locking of erbium-doped fiber optical frequency combs (OFCs). This study proposed a novel mathematical model to bridge the noise relationship of f_r between the free-running and locked modes, and analyzed this relationship from two perspectives: the additional phase noise and the frequency stability. In addition, to integrate theoretical modeling with experimental validation, this study designed f_r locking strategy that uses a phase-locked loop (PLL) with PFD + PIID (a phase frequency detector and a proportional, first-order integer, second-order integer, first-order differential controller). Under synchronization of the f_r with a microwave reference (REF), this study achieved OFC additional frequency stabilities of 2.81 × 10⁻¹⁵@1 s and 8.08 × 10⁻¹⁹@10,000 s at 200 MHz fundamental frequency locking and 4.25 × 10⁻¹⁶@1 s and 1.91 × 10⁻¹⁹@10,000 s at 1200 MHz harmonic locking. The simulated and experimental results are in good agreement, confirming the consistency of the theoretical model and experiment. This work provides a reliable theoretical model that can be used to predict stability for OFC locking and significantly improves the additional frequency stability of OFCs.

High-precision satellite-ground microwave time-frequency comparison links are crucial for space-time synchronization and clock performance evaluation. However, traditional hardware devices suffer from temperature-induced transmission delay drifts in RF cables and severe phase noise degradation during electronic frequency multiplication. To address these device-level bottlenecks, this paper proposes an advanced hardware-level optical frequency-assisted scheme for picosecond-level time difference measurement. To compensate for thermal delay drifts, a reflection-interferometer-based fiber phase-stabilization technique is developed using fringe counting for high-speed phase demodulation, achieving a measurement resolution of 1.29 fs @ 1550 nm and a typical compensation precision within 12 fs over a 24 h period. To suppress phase noise accumulation, a microwave photonic frequency synthesis technique based on Mach–Zehnder Interferometer (MZI) repetition-rate multiplication is established; the generated 30 GHz local oscillator (LO) signal achieves absolute phase noise of −120 dBc/Hz @ 1 kHz and −136 dBc/Hz @ 1 MHz. Laboratory benchtop testing and on-orbit verification demonstrate a sub-picosecond equipment-level random measurement noise (1 σ) for the microwave two-way time-difference measurement system. This study provides critical hardware-level technical support for satellite-ground time-frequency comparison links and spatial spatiotemporal reference construction.