title: A coherent fiber link for very long baseline interferometry.
abstract: We realize a coherent fiber link for application in very long baseline interferometry (VLBI) for radio astronomy and geodesy. A 550-km optical fiber connects the Italian National Metrological Institute (INRIM) to a radio telescope in Italy and is used for the primary Cs fountain clock stability and accuracy dissemination. We use an ultrastable laser frequency- referenced to the primary standard as a transfer oscillator; at the radio telescope, an RF signal is generated from the laser by using an optical frequency comb. This scheme now provides the traceability of the local maser to the SI second, realized by the Cs fountain at the 1.7 × 10(-16) accuracy. The fiber link never limits the experiment and is robust enough to sustain radio astronomical campaigns. This experiment opens the possibility of replacing the local hydrogen masers at the VLBI sites with optically-synthesized RF signals. This could improve VLBI resolution by providing more accurate and stable frequency references and, in perspective, by enabling common- clock VLBI based on a network of telescopes connected by fiber links.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Clivati
authors.forename: Giovanni A
authors.initials: GA
authors.lastname: Costanzo
authors.forename: Matteo
authors.initials: M
authors.lastname: Frittelli
authors.forename: Filippo
authors.initials: F
authors.lastname: Levi
authors.forename: Alberto
authors.initials: A
authors.lastname: Mura
authors.forename: Massimo
authors.initials: M
authors.lastname: Zucco
authors.forename: Roberto
authors.initials: R
authors.lastname: Ambrosini
authors.forename: Claudio
authors.initials: C
authors.lastname: Bortolotti
authors.forename: Federico
authors.initials: F
authors.lastname: Perini
authors.forename: Mauro
authors.initials: M
authors.lastname: Roma
authors.forename: Davide
authors.initials: D
authors.lastname: Calonico