We present high-reflectivity mechanical resonators fabricated from AlGaAs heterostructures for use in free-space optical cavities operating in the telecom wavelength regime. The mechanical resonators are fabricated in slabs of GaAs and patterned with a photonic crystal to increase their out-of-plane reflectivity. Characterization of the mechanical modes reveals residual tensile stress in the GaAs device layer. This stress results in higher mechanical frequencies than in unstressed GaAs and can be used for strain engineering of mechanical dissipation. Simultaneously, we find that the finite waist of the incident optical beam leads to a dip in the reflectance spectrum. This feature originates from coupling to a guided resonance of the photonic crystal, an effect that must be taken into account when designing slabs of finite size. The single- and sub-$\upmu$m-spaced double-layer slabs demonstrated here can be directly fabricated on top of a distributed Bragg reflector mirror in the same material platform. Such a platform opens a route for realizing integrated multi-element cavity optomechanical devices and optomechanical microcavities on chip.
Mechanical mode imaging of a high-Q hybrid hBN/Si$_3$N$_4$ resonator
我们的图像和表征的2D鼓谐振器的机械模式的hBN悬浮在高应力Si $_3$ N $_4$膜。我们的测量表明hBN谐振器和Si $_3$ N $_4$膜的各种模式之间的杂交。测得的谐振频率和空间分布的模式是一致的有限元模拟的基础上的理想化的几何形状。热运动的光谱显示，根据与较重和较高品质因数的Si $_3$ N $_4$膜的模式的杂化程度，hBN鼓模式的品质因数和运动质量可以移动数量级。这种效应可以被利用来设计混合鼓/膜模式，其将2D材料的低运动质量与Si $_3$ N $_4$膜的高品质因数相结合，用于光学机械或传感应用。
