The synthesis of ultralow-noise microwaves is of both scientific and technological relevance for timing, metrology, communications and radio-astronomy. Today, the lowest reported phase noise signals are obtained via optical frequency-division using mode-locked laser frequency combs. Nonetheless, this technique ideally requires high repetition rates and tight comb stabilisation. Here, a microresonator-based Kerr frequency comb (soliton microcomb) with a 14 GHz repetition rate is generated with an ultra-stable pump laser and used to derive an ultralow-noise microwave reference signal, with an absolute phase noise level below -60 dBc/Hz at 1 Hz offset frequency and -135 dBc/Hz at 10 kHz. This is achieved using a transfer oscillator approach, where the free-running microcomb noise (which is carefully studied and minimised) is cancelled via a combination of electronic division and mixing. Although this proof-of-principle uses an auxiliary comb for detecting the microcomb's offset frequency, we highlight the prospects of this method with future self-referenced integrated microcombs and electro-optic combs, that would allow for ultralow-noise microwave and sub-terahertz signal generators.

中文翻译：

---

超低噪声光子微波合成，使用基于孤子的微梳转移振荡器。

超低噪声微波的合成在时间，计量，通信和射电天文学方面具有科学和技术意义。如今，报告的最低相位噪声信号是通过使用锁模激光频率梳通过光学分频获得的。尽管如此，该技术理想地要求高重复率和紧密的梳状稳定度。在此，使用超稳定的泵浦激光器产生具有14 GHz重复频率的基于微谐振器的Kerr频率梳（孤子微梳），并用于导出绝对相位噪声电平低于-60 dBc的超低噪声微波参考信号偏移频率为1 Hz时为/ Hz，10 kHz时为-135 dBc / Hz。这是使用转移振荡器方法实现的，通过电子分频和混合，消除了自由运行的微梳子噪声（经过仔细研究和最小化）。尽管本原理证明使用辅助梳来检测微梳的偏移频率，但我们强调了该方法在未来自引用的集成微梳和电梳的前景，这将允许超低噪声的微波和亚太赫兹信号发生器。