The optical fiber link LIFT for radioastronomy

Optical fiber links are beneficial not only for frequency metrology, but also for other fields of physical research, such as radioastronomy and geodesy. We realized the first optical fiber link from a National Institute of Metrology to a Radiotelescope used for Very Long Baseline Interferometry and for geodetic measurements, over a distance of 544 km. We performed a remote calibration of the hydrogen-maser used as a frequency reference at Medicina Radiotelescopes, in central Italy, against the Italian Cs fountain primary frequency standard. The comparison was limited by the statistical uncertainty of the hydrogen-masers. This experiment demonstrates that optical links can provide radioastronomical facilities with very accurate and stable frequency references, in perspective better than the currently used hydrogen-masers. This opens new perspectives in the ultimate limits of VLBI and a more precise space geodesy.