Abstract
An absolutely consistent fiber-optic phase synchronization scheme based on fixed-phase-reference optical active compensation is proposed. By measuring the time interval of time pulse and the phase difference of frequency signal, and then using the optical delay line to compensate the phase change in real time according to a fixed phase reference, the phase period ambiguity and the phase-lock control initial randomness are eliminated, realizing a stable and repeatable fixed phase difference between different sites. Then the phase synchronization performances of stability and absolute consistence have been demonstrated through experiments in different scenarios. The phase difference fluctuation within 10000 s is only ±0.0006 rad, showing an ultra-high stability. Under the total of 5 different operations, including the signal source restart, system restart, adding 20 m additional fiber, adding 1 km additional fiber, and adding 2 km additional fiber, the maximum inconsistency of the mean phase difference is about 1% of one full cycle. The proposed and verified absolutely consistent phase synchronization method can well maintain the coherence in transferring frequency signal, having important application prospects in radar network and other time-frequency-phase synchronization-based coherent detection.
Highlights
In recent years, time and frequency synchronization technology has been continuously improved to meet the needs of many applications such as clock comparison and synchronization, precise navigation and timing, clock-based geodesy, and fundamental constant measurement [1]–[6]
This paper proposes an absolutely consistent fiber-optic phase synchronization scheme based on fixed-phase-reference optical active compensation
Due to asymmetry effect, the fluctuation of forward parameters are worse than round-trip parameters, and their absolute values is not the relationship of 2 times, which are the common problems of the two-way time-frequency transmission system
Summary
Time and frequency synchronization technology has been continuously improved to meet the needs of many applications such as clock comparison and synchronization, precise navigation and timing, clock-based geodesy, and fundamental constant measurement [1]–[6]. The phase difference is constant during each independent running state, but when the system experiences operations from shutdown to restart, or changing the length of fiber link, the phase difference value after entering the steady state again will change. This situation can no longer meet the needs of some coherence applications [13]–[16], which require the phase difference to remain stable (that is, frequency synchronization), and need absolutely consistent repeatable phase difference. The study of absolutely consistent phase synchronization is beginning to turn into important
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