Frequency comb synthesized microwaves have been so far realized with tabletop systems, operated in well-controlled environments. Here, we demonstrate state-of-the-art ultrastable microwave synthesis with a compact rack-mountable apparatus. We present absolute phase noise characterization of a 12 GHz signal using an ultrastable laser at $\sim{194}\;{\rm THz}$∼194THz and an Er:fiber comb divider, obtaining $ - {83}\;{\rm dBc/Hz}$-83dBc/Hz at 1 Hz and $ \lt - {166}\;{\rm dBc/Hz}$<-166dBc/Hz for offsets greater than 5 kHz. Employing semiconductor coating mirrors for the same type of transportable optical frequency reference, we show that $ - {105}\;{\rm dBc/Hz}$-105dBc/Hz at 1 Hz is supported by demonstrating a residual noise limit of division and detection process of $ - {115}\;{\rm dBc/Hz}$-115dBc/Hz at 1 Hz. This level of fidelity paves the way for the deployment of ultrastable photonic microwave oscillators and for operating transportable optical clocks.

中文翻译：

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紧凑，超稳定的光子微波振荡器。

迄今为止，频率梳合成的微波已经通过在可控环境中运行的台式系统实现。在这里，我们用紧凑的可机架安装的设备演示了最新的超稳定微波合成方法。我们使用$ \ sim {194} \; {\ rm THz} $〜194THz的超稳定激光和Er：纤维梳状分频器给出12 GHz信号的绝对相位噪声特性，得到$-{83} \; {\ rm dBc / Hz}-83dBc / Hz在1 Hz和$ \ lt-{166} \; {\ rm dBc / Hz} $ <-166dBc / Hz，对于大于5 kHz的偏移。对于相同类型的可移动光学频率参考，使用半导体镀膜镜，我们证明了1-Hz的$-{105} \; {\ rm dBc / Hz} $-105dBc / Hz可通过证明除数和$-{115} \; {\ rm dBc / Hz} $-115dBc / Hz在1 Hz时的检测过程。