Nanoscale optomechanical sensors: Split-beam photonic crystal nanocavities

Optomechanical nanocavities allow nanomechanical resonances to be measured optically with high sensitivity. We have created a new type of photonic crystal nanocavity optomechanical sensor optimized for detecting sources of torque and other forces which can deflect nanoscale cantilevers. This nanocavity consists of two precisely engineered photonic Bragg mirrors patterned in silicon cantilevers and separated by a 50-100 nm wide gap. Simulations of the optical and mechanical modes predict that mechanical displacements of the sub-picogram cantilevers will shift the optical nanocavity resonance frequency at a rate exceeding 20 GHz / nm, and that the nanocavity optical mode may have a quality factor Q_o > 10⁶ in optimized devices.