Abstract Cavity optomechanics has recently emerged as a new paradigm enabling the manipulation of mechanical motion via optical fields tightly confined in deformable cavities. When driving an optomechanical (OM) crystal cavity with a laser blue-detuned with respect to the optical resonance, the mechanical motion is amplified, ultimately resulting in phonon lasing at MHz and even GHz frequencies. In this work, we show that a silicon OM crystal cavity performs as an OM microwave oscillator when pumped above the threshold for self-sustained OM oscillations. To this end, we use an OM cavity designed to have a breathing-like mechanical mode at 3.897 GHz in a full phononic bandgap. Our measurements show that the first harmonic of the detected signal displays a phase noise of ≈−100 dBc/Hz at 100 kHz. Stronger blue-detuned driving leads eventually to the formation of an OM frequency comb, whose lines are spaced by the mechanical frequency. We also measure the phase noise for higher-order harmonics and show that, unlike in Brillouin oscillators, the noise is increased as corresponding to classical harmonic mixing. Finally, we present real-time measurements of the comb waveform and show that it can be fitted to a theoretical model recently presented. Our results suggest that silicon OM cavities could be relevant processing elements in microwave photonics and optical RF processing, in particular in disciplines requiring low weight, compactness and fiber interconnection.

中文翻译：

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全声子带隙硅光机腔中的微波振荡器和频率梳

摘要 空腔光力学最近成为一种新范式，能够通过紧密限制在可变形空腔中的光场来操纵机械运动。当使用相对于光学共振失谐的激光驱动光机械 (OM) 晶体腔时，机械运动被放大，最终导致声子在 MHz 甚至 GHz 频率下发射激光。在这项工作中，我们展示了当泵浦高于自持 OM 振荡的阈值时，硅 OM 晶体腔充当 OM 微波振荡器。为此，我们使用了一个 OM 腔，设计为在 3.897 GHz 的全声子带隙中具有类似呼吸的机械模式。我们的测量表明，检测到的信号的一次谐波在 100 kHz 下显示出 ≈−100 dBc/Hz 的相位噪声。更强的蓝失谐驱动最终导致形成 OM 频率梳，其线由机械频率隔开。我们还测量了高次谐波的相位噪声，并表明与布里渊振荡器不同，噪声随着经典谐波混合而增加。最后，我们展示了梳状波形的实时测量结果，并表明它可以拟合最近提出的理论模型。我们的结果表明，硅 OM 腔可能是微波光子学和光学 RF 处理中的相关处理元件，特别是在需要低重量、紧凑性和光纤互连的学科中。与布里渊振荡器不同，噪声随着经典谐波混合而增加。最后，我们展示了梳状波形的实时测量结果，并表明它可以拟合最近提出的理论模型。我们的结果表明，硅 OM 腔可能是微波光子学和光学 RF 处理中的相关处理元件，特别是在需要低重量、紧凑性和光纤互连的学科中。与布里渊振荡器不同，噪声随着经典谐波混频而增加。最后，我们展示了梳状波形的实时测量结果，并表明它可以拟合最近提出的理论模型。我们的结果表明，硅 OM 腔可能是微波光子学和光学 RF 处理中的相关处理元件，特别是在需要低重量、紧凑性和光纤互连的学科中。