In this paper, we demonstrate ultrastable radio-frequency (RF) transfer over long-haul optical fiber link. Our stabilized RF transfer technique is based on high-performance dual phase locked loops (dual-PLL) configuration which improves signal to noise ratio (SNR) of the round trip transmitted signals. At the local site, the frequency conversion phase-lock receiver (FCPLR) accomplishes high-quality phase tracking of the RF signal which is transmitted after long distance optical fiber link. The low phase noise signal generated by FCPLR is passively mixed with a local reference signal to realize phase conjugation. Through advisable frequency design, there is no residual RF leakage and nonlinear effect of frequency mixing. Another PLL incorporating a high-quality cleanup oscillator is located at the remote site that favourably improves short-term instability of our transmission system. In our experiment, stabilized 2.4 GHz RF signal transfer over a 1007 km optical fiber link is demonstrated without any electric relay system, and the transmission system achieves a fractional frequency instability of 8.20 × $10^{-14}$@1 s and 7.87 × $10^{-17}$@10 000 s.

中文翻译：

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基于双锁相环的超稳定长距离光纤射频传输

在本文中，我们展示了在长距离光纤链路上的超稳定射频 (RF) 传输。我们的稳定射频传输技术基于高性能双锁相环 (dual-PLL) 配置，可提高往返传输信号的信噪比 (SNR)。在本地，变频锁相接收器（FCPLR）对长距离光纤链路后传输的射频信号完成高质量的相位跟踪。FCPLR 产生的低相位噪声信号与本地参考信号无源混合以实现相位共轭。通过可取的频率设计，没有残留的射频泄漏和混频的非线性效应。另一个包含高质量清除振荡器的 PLL 位于远程站点，这有利于改善我们传输系统的短期不稳定性。在我们的实验中，在没有任何电中继系统的情况下，在 1007 公里的光纤链路上进行了稳定的 2.4 GHz 射频信号传输，传输系统实现了 8.20 × 的分数频率不稳定性$10^{-14}$@1 秒和 7.87 × $10^{-17}$@10 000 秒。