Abstract
Precision time synchronization between two remote sites is desired in many applications such as global positioning satellite systems, long-baseline interferometry, coherent radar detection and fundamental physics constant measurements. The recently developed frequency dissemination technologies based on optical fiber link have improved the transfer instability to the level of 10−19/day at remote location. Therefore it is possible to keep clock oscillation at remote locations continuously corrected, or to reproduce a “virtual” clock on the remote location. However the initial alignment and the correction of 1 pps timing signal from time to time are still required, besides the highly stabilized clock frequency transfer between distant locations. Here we demonstrate a time synchronization based on an ultra-stable frequency transfer system via 120-km commercial fiber link by transferring an optical frequency comb. Both the phase noise compensation in frequency dissemination and temporal basis alignment in time synchronization were implemented by a feed-forward digital compensation (FFDC) technique. The fractional frequency instability was measured to be 6.18 × 10−20 at 2000 s. The timing deviation of time synchronization was measured to be 0.6 ps in 1500 s. This technique also can be applied in multi-node fiber network topology.
Highlights
The NIST group[30] with the use of free-space optical link recently, the system became more configurable and flexible
We report a timing basis synchronization system with a feed-forward digital compensation (FFDC) scheme[31] based precision transferred frequency over a 120 km fiber link by using mode locked laser pulses
The time synchronization of a 1 pps was built based on the precision frequency transfer system
Summary
The time synchronization of a 1 pps was built based on the precision frequency transfer system. The total length and the loss of the fiber link measured by an OTDR (Optical Time Domain Reflectometer) were 120 km and 40.11 dB respectively Both the sender and receiver were located at the LB station marked as LB1 and LB2, for the system evaluation. The newly generated laser pulses were sent back to the local site for phase noise detection in the fiber link. The phase noise is digitally corrected at the remote end, rather than performed at the local end It was carried out by the phase shifter and the frequency recovery module (FRM) as shown in the Fig. 2. Fractional frequency instability and time synchronization measurement. We have demonstrated time synchronization with ultra-stable frequency transfer using mode locked pulse train as the RF carrier over 120-km telecommunication fiber link.
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