Fig. 1. Schematic overview of a single link stabilizing unit of the optical synchronization system of the EuXFEL.

Fig. 2. Overview of the method used to analyze the impact of seismic activities on the optical synchronization system.

Fig. 3. Results of analyzing of the 3.5 km link. (a) Spectrogram of October 2023. (b) Average PSD of October 2023. (c) Integrated jitter over the frequency range 0.005–5 Hz. (d) Integrated jitter over the frequency range 0.1–0.3 Hz, with earthquake effects removed. (e) Integrated jitter over the frequency range 0.9–3.5 Hz.

Fig. 4. Comparison of civilization noise (0.9–3.5 Hz) between working days and non-working days with respect to the time of day, averaged over 27 days.

Fig. 5. Influence of seismic activities on optical links leading to different tunnel positions at the EuXFEL. (a) The difference between the maximum and minimum integrated jitter values recorded over the month of October for each link, highlighting the variability in seismic impact. (b) The minimum integrated jitter observed during the same period, representing the baseline performance of the synchronization system under minimal seismic disturbance.

Fig. 6. Results of analyzing of the 3.5 km link. (a) Spectrogram of October 2023. (b) Average PSD of October 2023. (c) Integrated jitter over the frequency range 0.005–5 Hz. (d) Integrated jitter over the frequency range 0.1–0.3 Hz, with earthquake effects removed. (e) Integrated jitter over the frequency range 0.9–3.5 Hz.

Fig. 7. Spectrogram (a) and averaged PSD (b) of seismometer data in the EuXFEL tunnel direction.

Fig. 8. Comparison between seismometer data and the integrated jitters of controller output (a) and input (b).

Fig. 9. Comparison between the integrated jitters of controller output and earthquake intensities (a), sea level (b) and car counts (c).

Fig. 10. Spectrogram of controller I/O during Taylor Swift concert.