The force exerted by light is small and generally insignificant. However, optical forces (e.g. photothermal or radiation pressure) can have a profound influence on micro-/nano-mechanical devices. Cavity opto-mechanics is a multi-disciplinary field that exploits these forces by enhancing light-matter interactions via feedback. We are studying chip-scale integrated cavity optomechanical structures. Our aim is to develop fully-integrated devices that can take advantage of optical forces. The devices will be all-optical in their actuation and readout, i.e. they do not require any electrical power on-chip.

One such integrated cavity optomechanical system consists of a silicon microbridge oscillator coupled to a Fabry-Perot resonator. The optical cavity consists of two silicon/air grating mirrors, one of which is fixed while the other is attached to the microbridge oscillator. Any oscillator motion will displace the grating and tune the cavity transmission. Optical forces that are generated by the high intensity of light inside the cavity result in a change in the oscillator dynamics (i.e. oscillation amplitude, linewidth and frequency).

(a,b): Schematic and SEM of an integrated Fabry-Perot cavity opto-mechanical system, (c):Mechanical spectra measured at two different wavelengths showing the effect of optical forces on the oscillation dynamics.
(a,b): Schematic and SEM of an integrated Fabry-Perot cavity opto-mechanical system, (c):Mechanical spectra measured at two different wavelengths showing the effect of optical forces on the oscillation dynamics.

We are also interested in extending our optomechanics efforts to other architectures and material systems. In addition to silicon-based devices, silicon nitride, low-loss oxide, and compound semiconductor structures are of interest. We have demonstrated a linear-cavity optomechanics architecture and are also interested in microring cavities as well as optical forces in the absence of cavities.

(a): Waveguide with dielectric perturber suspended above it. (b): Side view of a released Si3N4 microbridge. The waveguide’s large evanescent optical field leads to a strong interaction with the microbridge.
(a): Waveguide with dielectric perturber suspended above it. (b): Side view of a released Si3N4 microbridge. The waveguide’s large evanescent optical field leads to a strong interaction with the microbridge.

An example of a different type of optomechanical system is shown below. This structure does not have a cavity. Optical forces arise from the large evanescent field of the waveguide. The optical mode extends beyond the waveguide surface so that evanescent field interaction with a dielectric perturber placed above the waveguide occurs. The resulting forces can be exploited in a variety of applications ranging from sensors to actuators to integrated optical components.