Frequency Noise of Silicon Nitride Optomechanical Oscillators with Integrated Waveguides

We demonstrate silicon nitride cavity optomechanical oscillators fabricated in a planar process adjacent to integrated coupling waveguides. Allan deviation of the mechanical oscillation frequency was characterized using a free-space optical setup in air. The device exhibited a frequency instability of 78 parts per billion at an averaging time of 130ms and fractional short-term instability of 2x10 ^-8 /τ ^1/2 . Benefits of the fabrication process include all-stepper lithography, planar topology, wafer-scale wet release, and waveguide facets formed by 220μm deep dry etching. Optical and mechanical Q=1450 at 58MHz in air were obtained in initial samples.