Stacked integrated double-disks for cavity optomechanics

The coupling of mechanical oscillators and optical cavity modes through scattering forces has received considerable attention in recent years. This interaction provides a way, through the principle of dynamic back action, to amplify and cool mechanical motion . It could also soon provide a practical means to entangle macroscopic mechanical motion with a variety of other quantum systems, including light. To date, experimental work has relied upon the optical scattering force to create conditions necessary for observation of dynamical back action effects. However, alongside the scattering force there are also dipole optical forces that can furnish optomechanical coupling. These forces, also referred to as dispersive or gradient forces, have been used to control coupling of a waveguide to a resonator and to couple pairs of waveguides. This paper demonstrates a stacked, double-disk whispering gallery system as a new means to cavity optomechanical phenomena. Dipole-force coupling between the disks creates optomechanical coupling, causing displacement of the disks and tuning of the underlying whispering gallery resonances. In comparison to scattering-force-based systems, this double-disk configuration has the significant advantage of providing a larger optomechanical coupling constant, independent of the cavity round trip length. The electromagnetic energy associated with the combined system is strongly dependent upon the separation of the disks, creating a mutual coupling force that is repulsive for excitation of the anti-symmetric mode (anti-bonding mode) and attractive for the symmetric mode (bonding mode). Strong regenerative oscillations are observed with a characteristic threshold.