Precise and Continuous Time and Frequency Synchronisation at the 5×10-19 Accuracy Level

Abstract

The synchronisation of time and frequency between remote locations is crucial for many important applications. Conventional time and frequency dissemination often makes use of satellite links. Recently, the communication fibre network has become an attractive option for long-distance time and frequency dissemination. Here, we demonstrate accurate frequency transfer and time synchronisation via an 80 km fibre link between Tsinghua University (THU) and the National Institute of Metrology of China (NIM). Using a 9.1 GHz microwave modulation and a timing signal carried by two continuous-wave lasers and transferred across the same 80 km urban fibre link, frequency transfer stability at the level of 5×10−19/day was achieved. Time synchronisation at the 50 ps precision level was also demonstrated. The system is reliable and has operated continuously for several months. We further discuss the feasibility of using such frequency and time transfer over 1000 km and its applications to long-baseline radio astronomy.

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.…”

Accurate and fast fiber transfer delay measurement based on phase discrimination and frequency measurement

“…The fiber transfer delay (FTD), as an essential characteristic for fiber transmission, becomes a significant parameter in many optical fiber applications, such as optical communication [1][2][3], fiber timing distribution system [4][5][6], phased array antenna [7][8][9] and some other large-scale scientific or engineering facilities [10][11][12][13]. Up to now, many techniques for FTD measurement in time domain or frequency domain have been developed and successfully employed [14][15][16][17][18][19][20][21].…”

Highly accurate fiber transfer delay measurement with large dynamic range

“…For the application of phased array antenna, fiber transfer delay (FTD) measurement accuracy directly affects its control accuracy, and further affects the beam forming results [7][8][9][10]. For time and frequency synchronization network, FTD measurement is a key step to realize clock synchronization [11][12][13][14]. Ordinarily, the time delay is measured in time domain, such as using the time interval counter (TIC) [15] or optical time domain reflectometer (OTDR) [16], but they have drawbacks of low accuracy and existing dead zones.…”