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arXiv · 2510.21132

Centi-combs: Low-noise sub-GHz repetition-rate soliton frequency combs from crystalline resonators

Tatsuki Murakami·Keisuke Ogawa·Hajime Kumazaki·Shun Fujii
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Abstract

We demonstrate low-noise Kerr soliton frequency combs with repetition rates below 1~GHz in ultrahigh-Q crystalline magnesium fluoride resonators. Single soliton states with repetition rates of 0.90 GHz, 1.19 GHz, 1.59 GHz, 2.48 GHz, and 4.10 GHz are observed with continuous-wave laser excitation. The near-GHz soliton repetition frequency exhibits a single-sideband phase noise of -137 dBc/Hz at a 100 kHz offset, surpassing state-of-the-art microwave generators. These ``centi-combs'' bridge the gap between conventional mode-locked lasers and microresonator frequency combs, providing a new route towards real-time sampling, optical-to-microwave synchronization, and hybrid optical clock networks in a compact form. This work expands the operational range of Kerr soliton microcombs from the terahertz to the sub-gigahertz domain, opening new frontiers for frequency comb technologies.

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Tatsuki Murakami, Keisuke Ogawa, Hajime Kumazaki, Shun Fujii. 2025-10-24. Centi-combs: Low-noise sub-GHz repetition-rate soliton frequency combs from crystalline resonators. https://doi.org/10.1364/ol.588924

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