With demonstrated applications ranging from metrology to telecommunications, soliton microresonator frequency combs have emerged over the past decade as a remarkable new technology. However, standard implementations allow only for the generation of combs whose repetition rate is tied closely to the fundamental resonator free-spectral range (FSR), offering little or no dynamic control over the comb line spacing. Here we propose and experimentally demonstrate harmonic and rational harmonic driving as novel techniques that allow for the robust generation of soliton frequency combs with discretely adjustable frequency spacing. By driving an integrated Kerr microresonator with a periodic train of picosecond pulses whose repetition rate is set close to an integer harmonic of the 3.23 GHz cavity FSR, we deterministically generate soliton frequency combs with frequency spacings discretely adjustable between 3.23 GHz and 19.38 GHz. More remarkably, we also demonstrate that driving the resonator at rational fractions of the FSR allows for the generation of combs whose frequency spacing corresponds to an integer harmonic of the pump repetition rate. By measuring the combs’ radio-frequency spectrum, we confirm operation in the low-noise soliton regime with no supermode noise. The novel techniques demonstrated in our work provide new degrees of freedom for the design of synchronously pumped soliton frequency combs.

中文翻译：

---

微谐振器孤子频率梳的谐波和合理谐波驱动

随着从计量学到电信领域的广泛应用，孤子微谐振器频率梳在过去的十年中已成为一项非凡的新技术。但是，标准实现仅允许生成其重复频率与基本谐振器自由光谱范围（FSR）紧密相关的梳子，从而几乎无法提供对梳齿线间距的动态控制。在这里，我们提出并通过实验证明了谐波和合理的谐波驱动是一种新颖的技术，可以使孤子频率梳可靠地生成，并具有可离散调节的频率间隔。通过用周期的皮秒脉冲序列驱动集成的Kerr微谐振器，其重复频率设置为接近3.23 GHz腔FSR的整数谐波，我们确定性地生成孤子频率梳，其频率间隔可在3.23 GHz至19.38 GHz之间离散可调。更值得注意的是，我们还证明了以FSR的合理分数驱动谐振器可以产生梳齿，其频率间隔对应于泵重复频率的整数谐波。通过测量梳子的射频频谱，我们确认了在无超模噪声的低噪声孤子状态下的工作。我们工作中展示的新颖技术为同步泵浦孤子频率梳的设计提供了新的自由度。我们还证明，以FSR的合理分数驱动谐振器可以产生梳齿，其频率间隔对应于泵重复频率的整数谐波。通过测量梳子的射频频谱，我们确认了在无超模噪声的低噪声孤子状态下的工作。我们工作中展示的新颖技术为同步泵浦孤子频率梳的设计提供了新的自由度。我们还证明，以FSR的合理分数驱动谐振器可以产生梳齿，其频率间隔对应于泵重复频率的整数谐波。通过测量梳子的射频频谱，我们确认了在无超模噪声的低噪声孤子状态下的工作。我们工作中展示的新颖技术为同步泵浦孤子频率梳的设计提供了新的自由度。