Characterization of a 450-km Baseline GPS Carrier-Phase Link using an Optical Fiber Link

TL;DR

This paper demonstrates the characterization of a 450-km GPS carrier-phase frequency transfer link by comparing it with a 920-km optical fiber link, achieving high stability and confirming measurement accuracy over long distances.

Contribution

It presents a novel method for characterizing long-distance GPS frequency transfer links using optical fiber comparisons, validating the link stability and measurement uncertainty.

Findings

Frequency instability of 3 x 10^(-13) at 30 s

Long-term frequency stability of 5 x 10^(-16)

No deviation larger than 6 x 10^(-16) between links

Abstract

A GPS carrier-phase frequency transfer link along a baseline of 450 km has been established and is characterized by comparing it to a phase-stabilized optical fiber link of 920 km length, established between the two endpoints, the Max-Planck-Institut f\"ur Quantenoptik in Garching and the Physikalisch-Technische Bundesanstalt in Braunschweig. The characterization is accomplished by comparing two active hydrogen masers operated at both institutes. The masers serve as local oscillators and cancel out when the double differences are calculated, such that they do not constitute a limitation for the GPS link characterization. We achieve a frequency instability of 3 x 10^(-13) in 30 s and 5 x 10^(-16) for long averaging times. Frequency comparison results obtained via both links show no deviation larger than the statistical uncertainty of 6 x 10^(-16). These results can be interpreted as a successful cross-check of the measurement uncertainty of a truly remote end fiber link.