Time transfer through optical fibres over a distance of 73 km with an uncertainty below 100 ps

Abstract

We demonstrate the capability of accurate time transfer using optical fibers over long distances utilizing a dark fiber and hardware which is usually employed in two-way satellite time and frequency transfer (TWSTFT). Our time transfer through optical fiber (TTTOF) system is a variant of the standard TWSTFT by employing an optical fiber in the transmission path instead of free-space transmission of signals between two ground stations through geostationary satellites. As we use a dark fiber there are practically no limitations to the bandwidth of the transmitted signals so that we can use the highest chip-rate of the binary phase-shift modulation available from the commercial equipment. This leads to an enhanced precision compared to satellite time transfer where the occupied bandwidth is limited for cost reasons. The TTTOF system has been characterized and calibrated in a common clock experiment at PTB, and the combined calibration uncertainty is estimated as 74 ps. In a second step the remote part of the system was operated at Leibniz Universität Hannover, Institut für Quantenoptik (IQ) separated by 73 km from PTB in Braunschweig. In parallel, a GPS time transfer link between Braunschweig and Hannover was established, and both links connected a passive hydrogen maser at IQ with the reference time scale UTC(PTB) maintained in PTB. The results obtained with both links agree within the 1-σ uncertainty of the GPS link results, which is estimated as 0.72 ns. The fiber link exhibits a nearly 10-fold improved stability compared to the GPS link, and assessment of its performance has been limited by the properties of the passive maser.

Simultaneous remote transfer of accurate timing and optical frequency over a public fiber network

“…A salient case is the neutrinos speed measurement from CERN to Gran Sasso. Fiber-optical two-way time transfer methods have been demonstrated on dedicated links with an accuracy of the order of 100 ps or better [10,11]. Long-distance accurate time dissemination is usually based on GNSS signals, or geostationary telecommunication satellites, with timing accuracy of the order of 1 ns in the best case [12,13].…”

Frequency transfer via a two-way optical phase comparison on a multiplexed fiber network

“…Phase-compensated optical links have proved to be reliable from this point of view and outperform state-ofthe-art satellite techniques by orders of magnitude [4]. The trasmission of RF and microwaves [5][6][7][8][9], optical frequencies [10][11][12][13], and of an optical comb [14] have been demonstrated, and time dissemination has recently been performed as well [15][16][17]. In coherent optical links the phase noise added by the fiber due to environmental noise is actively cancelled.…”

Delivering 10 Gb/s optical data with picosecond timing uncertainty over 75 km distance

“…To our knowledge, the 4 ps measurement uncertainty reported here represents the most accurate long-haul signal propagation delay measurement to date, outperforming state-of-theart satellite methods by at least one order of magnitude [2,3], as well as recently reported techniques for fiber-optical time transfer [5][6][7]. When implemented in a TWTT system, our method may also improve on the reach, communication bandwidth, and timing uncertainty of current state-of-the-art methods for simultaneous data and time transfer (sub-nanosecond and 1 Gb/s over up to 10 km distance) [12,13].…”