Two-Dimensional Phononic-Photonic Band Gap Optomechanical Crystal Cavity

We present the fabrication and characterization of an artificial crystal structure formed from a thin film of silicon that has a full phononic band gap for microwave X-band phonons and a two-dimensional pseudo-band gap for near-infrared photons. An engineered defect in the crystal structure is used to localize optical and mechanical resonances in the band gap of the planar crystal. Two-tone optical spectroscopy is used to characterize the cavity system, showing a large coupling (g₀/2π≈220 kHz) between the fundamental optical cavity resonance at ωₒ/2π=195 THz and colocalized mechanical resonances at frequency ωₘ/2π≈9.3 GHz.