We demonstrate frequency-comb-based optical two-way time-frequency transfer across a three-node clock network. A fielded, bidirectional relay node connects laboratory-based master and end nodes, allowing the network to span 28 km of turbulent outdoor air while keeping optical transmit powers below 5 mW. Despite the comparatively high instability of the free-running local oscillator at the relay node, the network transfers frequency with fractional precision below 10⁻¹⁸ at averaging times above 200 s and transfers time with a time deviation below 1 fs at averaging times between 1 s and 1 h. The successful operation of this network represents a promising step toward the operation of future free-space networks of optical atomic clocks.

中文翻译：

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跨自由空间三节点网络的光时频传输

我们演示了跨三节点时钟网络的基于频梳的光学双向时频传输。一个现场的双向中继节点连接基于实验室的主节点和终端节点，从而使网络能够跨越28 km的湍流室外空气，同时将光传输功率保持在5 mW以下。尽管中继节点上的自由运行本地振荡器的不稳定性相对较高，但网络在200 s以上的平均时间传输分数精度低于10 ^-18的频率，并在1 s的平均时间传输时间偏差低于1 fs的时间1小时 该网络的成功运行是朝着未来的光学原子钟自由空间网络运行迈出的有希望的一步。