Recent works on Kerr frequency combs demonstrated the possibility to simultaneously generate multiple soliton states with different group velocities in a single microresonator, which could be beneficial for many applications utilizing dual-comb systems. In this work we demonstrate a dual-comb configuration in a single crystalline microresonator by monochromatically pumping counter-propagating solitons in the same spatial mode with equal powers. Moreover, we demonstrate experimentally and through simulations the key role of Cherenkov radiation interferences on the repetition rate of a multi-soliton state. This result not only shines new light on the impact of dispersive waves on dissipative Kerr solitons but also introduces a novel approach to develop coherent dual-comb spectrometer based on microcombs.
Nonlinear wave mixing in optical microresonators new perospects for compact optical frequency combs with many promising applications. We demonstrate simultaneous generation of multiple frequency combs from a single optical microresonator and a single continuous-wave laser. Similar to space-division multiplexing, we generate several dissipative Kerr soliton states – circulating solitonic pulses driven by a continuous-wave laser – in different spatial (or polarization) modes of a MgF2 microresonator. Up to three distinct combs are produced simultaneously, featuring excellent mutual coherence and substantial repetition rate differences, useful for fast acquisition and efficient rejection of soliton intermodulation products. This method could enable the deployment of dual- and triple-comb-based methods to applications where they remained impractical with current technology.
Photonic synthesis of radio frequency waveforms revived the quest for unrivalled microwave purity by its seducing ability to convey the benefits of the optics to the microwave world. In this contribution, we will present a high-fidelity transfer of frequency stability between an optical reference and a microwave signal via a low-noise fiber-based frequency comb and cutting-edge photo-detection techniques. We will show the generation of the purest microwave signal with a fractional frequency stability below 6.5×10-16 at 1 s and a timing noise floor below 41 zs Hz-1/2 (phase noise below -173 dBc Hz-1 for a 12 GHz carrier). This outclasses existing sources and promises a new era for state-of-the-art microwave generation. The characterization is achieved through a heterodyne cross-correlation scheme with lowermost detection noise. This unprecedented level of purity can impact domains such as radar systems, telecommunications and time-frequency metrology. The measurements methods developed here can benefit the characterization of a broad range of signals.
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