Effective reference clock signal in spaceborne gravitational-wave detection
Phys. Rev. Applied 24, 014014 – Published 7 July, 2025
DOI: https://doi.org/10.1103/r4pw-pznn
Abstract
In spaceborne gravitational-wave (GW) detectors, each satellite employs an ultrastable oscillator (USO) as a clock reference to trigger the analog-to-digital converter (ADC) for digital processing. Achieving precise timekeeping is vital for attaining the required detection sensitivity. However, both ADC aperture jitter and sampling clock jitter can disrupt the sampling timing, leading to distortion in the digitized signal and significantly compromising measurement accuracy. To mitigate these issues, spaceborne GW detection typically involves two steps: first, applying pilot-tone correction to the digitized data to eliminate ADC aperture jitter noise, and second, using clock-noise-cancellation techniques to suppress clock jitter noise, ultimately satisfying the detection requirements for spaceborne GWs. Yet, currently, there is a lack of clear elucidation on the effective clock reference within the satellite after pilot-tone correction, which is also the target of the clock-noise-cancellation technique. Clarifying this point is crucial, as it not only elucidates the physical mechanism through which clock noise affects GW detection but also guides the formulation of parameter indicators for the frequency distribution system at the experimental level. In this paper, we theoretically demonstrate, based on the fundamental principles of phase measurement, that the pilot tone becomes the effective clock reference after pilot-tone correction. Furthermore, when applying typical clock-noise-cancellation techniques to suppress pilot frequency jitter, it is crucial to ensure a high degree of coherence between the modulation frequency and the pilot frequency. To further validate this clock reference issue, we conducted electrical experiments using square waves to synchronize various clock drive frequencies. The experimental results are consistent with the theoretical predictions, demonstrating that the additional noise is better than the level of in the 1 mHz to 1 Hz frequency bandwidth, which falls below the fundamental noise level of typical spaceborne GW detectors.
