Common-clock very long baseline interferometry using a coherent optical fiber link

Abstract

Among the most powerful techniques for the exploration of the Universe is very long baseline interferometry (VLBI), which is based on the simultaneous observation of radio sources in the sky with arrays of distant ground-based antennas. One of the effects currently limiting its ultimate sensitivity is the phase-instability of the reference clocks adopted at each antenna. This term can be made negligible delivering the same clock signal to multiple telescope sites using optical fibers. We realized such an infrastructure by disseminating a coherent optical frequency signal to two distant radio telescopes using a 1739-km-long fiber. We performed a 24 h geodetic VLBI campaign in which the same clock reference was used at both telescopes and analyzed it using standard VLBI procedures. The results were consistent with the expectations, confirming that the proposed approach is feasible and configures as a novel tool for studying the role of clocks, troposphere, and systematic effects in the ultimate VLBI resolution.

Comparing ultrastable lasers at 7 × 10−17 fractional frequency instability through a 2220 km optical fibre network

“…Dissemination of ultrastable light has broad impact, with applications including characterisation of distant laser sources, precision spectroscopy with improved time and frequency distribution 43 – 46 and seismology through optical fibres 47 . Recent demonstrations of high fidelity transfer of the properties of metrological light from the optical domain to the microwave 48 , 49 and radio frequency 50 , 51 domain, further extend the range of applications of this work to radar 52 , navigation, telecommunication, quantum communication 53 , radio astronomy, synchronisation of radio telescope arrays, very long baseline interferometry (VLBI) 50 , 51 , geodesy and frequency comparison through VLBI 54 , 55 , deep-space communication and tracking 56 .…”

Coherent phase transfer for real-world twin-field quantum key distribution

“…The average loss coefficient of 0.3 dB/km is higher than the specified level for standard optical fibers (0.2 dB/km) and includes discrete losses of the connectors and DWDM equipment, which play a significant role in deployed networks. These fibers are part of the Italian Quantum Backbone and carry other services, among which is the dissemination of atomic clock signals to research facilities of the Country 38 , 39 . Conventionally, telecom networks support two-way data exchange over fiber pairs, in which each fiber allows light propagation in a single direction.…”

“…We propose a solution derived from frequency metrology, where the transmission of coherent laser radiation over thousand-kilometer distances is employed to compare distant atomic clocks at the highest accuracy 38 – 44 using ultrastable lasers and phase-stabilized optical fibers 45 .…”

Infrared Comb Spectroscopy of Buffer-Gas-Cooled Molecules: Toward Absolute Frequency Metrology of Cold Acetylene

“…In this configuration, fractional accuracy levels below are potentially within the reach. Correspondingly, as for the metrological scheme, the OFC to which the spectroscopic probe laser is phase-locked must be stabilized against a frequency standard with superior performance, such as a Cs primary fountain clock or a state-of-the-art optical frequency standard, as operated by Metrological Institutes and delivered by actively stabilized fiber links [ 123 , 124 , 125 , 126 ].…”