Microwave photonic technologies, which upshift the carrier into the optical domain, have facilitated the generation and processing of ultra-wideband electronic signals at vastly reduced fractional bandwidths. For microwave photonic applications such as radars, optical communications and low-noise microwave generation, optical frequency combs are useful building blocks. By virtue of soliton microcombs, frequency combs can now be built using CMOS-compatible photonic integrated circuits. Yet, currently developed integrated soliton microcombs all operate with repetition rates significantly beyond those that conventional electronics can detect, preventing their use in microwave photonics. Access to this regime is challenging due to the required ultra-low waveguide loss and large dimensions of the nanophotonic resonators. Here, we demonstrate soliton microcombs operating in two widely employed microwave bands, the X-band (~10 GHz, for radar) and the K-band (~20 GHz, for 5G). Driven by a low-noise fibre laser, these devices produce more than 300 frequency lines within the 3 dB bandwidth, and generate microwave signals featuring phase noise levels comparable to modern electronic microwave oscillators. Our results establish integrated microcombs as viable low-noise microwave generators. Furthermore, the low soliton repetition rates are critical for future dense wavelength-division multiplexing channel generation schemes and could significantly reduce the system complexity of soliton-based integrated frequency synthesizers and atomic clocks.

微波光子技术可将载波上移到光域，从而促进了以大大降低的分数带宽产生和处理超宽带电子信号。对于诸如雷达，光通信和低噪声微波产生之类的微波光子应用，光频率梳是有用的构件。借助于孤子微梳，现在可以使用兼容CMOS的光子集成电路来构建频率梳。但是，当前开发的集成孤子微梳子的重复率都大大超过了常规电子设备可以检测到的重复率，从而阻止了它们在微波光子学中的使用。由于所需的超低波导损耗和纳米光子谐振器的大尺寸，进入该体系具有挑战性。这里，我们演示了孤子微梳在两个广泛使用的微波频带（X频带（约10 GHz，用于雷达）和K频带（约20 GHz，用于5G）中工作）。这些设备由低噪声光纤激光器驱动，可在3 dB带宽内产生300条以上的频率线，并产生具有可与现代电子微波振荡器媲美的相位噪声水平的微波信号。我们的研究结果将集成的微梳子确立为可行的低噪声微波发生器。此外，低孤子重复率对于将来的密集波分复用信道生成方案至关重要，并且可以显着降低基于孤子的集成频率合成器和原子钟的系统复杂性。这些设备由低噪声光纤激光器驱动，可在3 dB带宽内产生300条以上的频率线，并产生具有可与现代电子微波振荡器媲美的相位噪声水平的微波信号。我们的结果将集成的微梳子确立为可行的低噪声微波发生器。此外，低孤子重复率对于将来的密集波分复用信道生成方案至关重要，并且可以显着降低基于孤子的集成频率合成器和原子钟的系统复杂性。这些设备由低噪声光纤激光器驱动，可在3 dB带宽内产生300条以上的频率线，并产生具有可与现代电子微波振荡器媲美的相位噪声水平的微波信号。我们的研究结果将集成的微梳子确立为可行的低噪声微波发生器。此外，低孤子重复率对于将来的密集波分复用信道生成方案至关重要，并且可以显着降低基于孤子的集成频率合成器和原子钟的系统复杂性。我们的结果将集成的微梳子确立为可行的低噪声微波发生器。此外，低孤子重复率对于将来的密集波分复用信道生成方案至关重要，并且可以显着降低基于孤子的集成频率合成器和原子钟的系统复杂性。我们的结果将集成的微梳子确立为可行的低噪声微波发生器。此外，低孤子重复率对于将来的密集波分复用信道生成方案至关重要，并且可以显着降低基于孤子的集成频率合成器和原子钟的系统复杂性。