We study experimentally a chain of defect resonators in a phononic crystal slab and observe its collective resonances at ultrasonic frequencies of a few megahertz. A phononic crystal of cross holes is fabricated in a thin fused-silica plate by femtosecond-laser writing followed by $\mathrm{KOH}$ etching. A chain of 17 coupled resonators is defined with no definite spatial periodicity but similar coupling strength between nearest-neighbor resonators. The full phononic band gap ensures that only evanescent waves in the crystal can tunnel between adjacent resonators in the plane. The resulting evanescent-coupling strength decreases exponentially with distance. Collective resonances are excited by a frequency-driven piezoelectric vibrator attached at one end of the chain and imaged along the chain with a laser Doppler vibrometer. A discrete spectrum of resonances is observed and explained by a model representing the chain as a phononic polymer. The theoretical analysis is supported by finite-element simulations that agree well with experimental results. Chains of evanescently coupled microresonators forming phononic polymers could find applications in ultrasonic sensing, for implementation in topological phononics, and for the design of optomechanical resonator chains.

中文翻译：

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耦合声子微谐振器链的集体共振。

我们通过实验研究了声子晶体平板中的一系列缺陷谐振器，并观察了其在几兆赫兹的超声频率下的集体谐振。通过飞秒激光写入，然后在飞秒激光石英薄板上制造出交叉孔的声子晶体$\mathrm{酸值}$蚀刻。定义了一个由17个耦合谐振器组成的链，没有明确的空间周期性，但是在最近的谐振器之间具有相似的耦合强度。完整的声带隙确保只有晶体中的e逝波才能在平面中的相邻谐振器之间隧穿。产生的消逝耦合强度随距离呈指数下降。聚集在链条一端的频率驱动压电振动器激发集体共振，并用激光多普勒振动计沿链条成像。观察到离散的共振频谱，并通过将链表示为声子聚合物的模型进行了解释。理论分析得到了与实验结果吻合的有限元模拟的支持。