Optical clocks with an unprecedented accuracy of ${10}^{-18}$ promise innovations in precision spectroscopy and measurement. To harness the full power of optical clocks, we need optical frequency synthesizers (OFSs) to accurately convert the stabilities and accuracies of optical clocks to other desired frequencies. This work demonstrates such an OFS referenced to an ytterbium optical clock. The OFS is based on an optical frequency comb phase-locked to a commercial rubidium microwave clock; in this way most combs can operate robustly. Despite comb frequency instability at ${10}^{-11}$, the synthesis noise and uncertainty reach $6\times {10}^{-18}$ (1 s) and $5\times {10}^{-21}$, respectively, facilitating frequency synthesis of the best optical clocks. In the OFS, the coherence of the OFS internal oscillator at 1064 nm is accurately transferred to a 578 nm laser for resolving the hertz-level-linewidth ytterbium clock transition (unaffected by megahertz-linewidth comb lines) and faithfully referencing the OFS to an ytterbium optical clock.

中文翻译：

---

以frequency光钟为参考的光频率合成器

具有前所未有的精度的光学时钟 ${10}^{-\mathrm{18岁}}$承诺在精密光谱学和测量领域进行创新。为了充分利用光学时钟的功率，我们需要光学频率合成器（OFS）将光学时钟的稳定性和准确性准确地转换为其他所需的频率。这项工作演示了这种OF原子钟的OFS。OFS基于锁相到商用rub微波时钟的光频率梳；通过这种方式，大多数梳子都可以稳定运行。尽管梳齿频率不稳定${10}^{-11}$，合成噪声和不确定性达到 $6\times {10}^{-\mathrm{18岁}}$ （1 s）和 $5\times {10}^{-21}$分别促进最佳光时钟的频率合成。在OFS中，将OFS内部振荡器在1064 nm处的相干性准确地转移到578 nm激光器，以解决赫兹级线宽时钟转换（不受兆赫线宽梳状线的影响），并忠实地将OFS称为refer光学时钟。