基于被动相位噪声补偿的自由空间光学频率传递

针对自由空间光信号传输更易受到环境影响的特点，提出了一种被动相位噪声补偿技术。该方法利用探测往返传输的光信号与发射端参考信号拍频获得链路引入的相位噪声，在发射端通过声光移频器（acousto-optic modulator, AOM）对待传递信号移频取共轭即可在接收端获得相位稳定的光学频率信号。该方法避免了使用复杂的鉴相和伺服控制电路，使系统具有更快的补偿速度且没有鉴相范围的限制。实验结果表明，150 m的室外自由空间链路的平均时间1 s的附加频率不稳定度约为1.9×10-16，平均时间1 000 s的附加频率不稳定度约为4.6×10-19。该相位噪声补偿技术为高精度的自由空间光学频率传递提供了一个简单可靠的方案。

Free space optical frequency transfer based on passive phase noise compensation

A passive phase noise compensation method is proposed for free space optical signal transmission which can be easily affected by the environment. In this method, phase noise introduced by the link is detected by the beatnote of the round-trip transmission optical signal and the reference optical signal at the transmitting site. An acousto-optic modulator (AOM) is used to shift and conjugate the frequency at the transmitting site. Thus, the phase stable optical frequency signal is obtained at the receiving site. This method avoids the use of complex phase discrimination and servo control circuits, making the transfer system have a faster compensation speed without any phase discrimination range limitations. The experimental results show that the fractional frequency instability is 1.9×10-16 at the integration time of 1 s and 4.6×10-19 at the integration time of 1 000 s for the 150 m outdoor free space link. The proposed phase noise compensation method provides a simple and reliable scheme for high precision free space optical frequency transfer.