A VLBI experiment using a remote atomic clock via a coherent fibre link

Area of Science:

• Geodesy
• Radio Astronomy
• Metrology

Background:

• Accurate timing is crucial for high-precision geodetic measurements using Very Long Baseline Interferometry (VLBI).
• Traditional clock synchronization methods in VLBI can be limited by distance and stability.

Purpose of the Study:

• To test the feasibility of delivering a precise clock reference from a National Metrology Institute to a radio telescope via a long-distance coherent fiber link.
• To evaluate the performance of VLBI geodetic campaigns using fiber-disseminated optical signals for clock synchronization.

Main Methods:

• A 550 km coherent fiber link was established to transmit a clock reference from a National Metrology Institute.
• A 24-hour geodetic VLBI campaign was conducted using European telescopes.
• At the Medicina radio telescope, a local clock was alternated with a signal from an optical comb slaved to the fiber-disseminated optical signal.

Main Results:

• Interferometric fringes were detected continuously throughout the 24-hour observation period.
• VLBI data processed with the fiber-disseminated clock reference yielded results with residuals comparable to those obtained with a local clock.
• The experiment confirmed the viability of using a fiber link for precise clock dissemination in VLBI.

Conclusions:

• Fiber-disseminated optical signals can effectively deliver precise clock references for VLBI over long distances.
• This technology shows promise for achieving ultimate VLBI performance with state-of-the-art atomic clocks.
• Further research is encouraged to explore the full potential of this method for enhancing VLBI precision.