Very-long-baseline interferometry (VLBI) for high-resolution astronomical imaging requires phase-stable frequency references at widely separated radio-telescope antennas. For the first time to our knowledge, we have disseminated a suitable radio-frequency (RF) reference for VLBI over a “real-world” telecom optical-fiber link between radio telescopes that are $>100\mathrm{km}$ apart, by means of an innovative phase-conjugation technique. Bidirectional optical amplification is used in parallel with live traffic, and phase perturbations in the effective optical-fiber path length are compensated. This RF-over-fiber approach obviates the need for separate hydrogen masers at each antenna, offering significant advantages for radio-astronomy facilities such as the Square Kilometer Array.

中文翻译：

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射电天文射频基准的长距离电信光纤传输

用于高分辨率天文成像的超长基线干涉测量（VLBI）要求在相距很远的射电望远镜天线上具有相位稳定的频率参考。据我们所知，这是我们首次通过无线电望远镜之间的“实际”电信光纤链路分发了适合VLBI的射频（RF）参考。$>100\mathrm{公里}$通过创新的相位共轭技术。双向光放大与实时流量并行使用，并且可以补偿有效光纤路径长度中的相位扰动。这种基于光纤的射频方法无需在每个天线上使用单独的氢激射器，从而为射电天文设施（例如平方公里阵列）提供了显着的优势。