Twisting an optomechanical cavity

Mechanical rotation and oscillation have far lower frequencies than light does; thus they are not coupled to each other conventionally. In this Letter, we show that the torsional mechanical oscillation of an optical cavity can be coupled to the optical modes by introducing birefringence, which produces nondegenerate modes in the cavity: ordinary and extraordinary rays. Twisting the cavity mixes them and modulates the electromagnetic energy. We find the torsional optomechanical Hamiltonian by quantizing the total energy and reveal that the torsional oscillation can be resonantly driven by light.