High-accuracy coherent optical frequency transfer over a doubled 642-km fiber link

• DOI: 10.1007/s00340-014-5917-8
• Publication Date: 2014-09-03T08:15:05Z
• Authors: D. Calonico; E. K. Bertacco; C. E. Calosso; C. Clivati; G. A. Costanzo; M. Frittelli; A. Godone; A. Mura; N. Poli; D. V. Sutyrin; G. Tino; M. E. Zucco; F. Levi
• Keywords: Allan variance; Optical link; Time transfer; Link (geometry)

To significantly improve the frequency references used in radio-astronomy and precision measurements in atomic physics, we provide frequency dissemination through a 642 km coherent optical fiber link, that will be also part of a forthcoming European network of optical links. We obtained a resolution of 3e-19 at 1000 s on the frequency transfer, and an accuracy of 5e-19. The ultimate link performance has been evaluated by doubling the link to 1284 km, demonstrating a new characterization technique based on the double round-trip on a single fiber. The arming of a second fiber is avoided: this is beneficial to long hauls realizations in view of a continental fiber network for frequency and time metrology. The data analysis is based on the Allan deviation; its expression is theoretically derived for the observed noise power spectrum, which is seldom found in the literature.