  Structured, periodic optical materials can be used to form photonic crystals
capable of dispersing, routing, and trapping light. A similar phenomena in
periodic elastic structures can be used to manipulate mechanical vibrations.
Here we present the design and experimental realization of strongly coupled
optical and mechanical modes in a planar, periodic nanostructure on a silicon
chip. 200-Terahertz photons are co-localized with mechanical modes of Gigahertz
frequency and 100-femtogram mass. The effective coupling length, which
describes the strength of the photon-phonon interaction, is as small as 2.9
microns, which, together with minute oscillator mass, allows all-optical
actuation and transduction of nanomechanical motion with near quantum-limited
sensitivity. Optomechanical crystals have many potential applications, from
RF-over-optical communication to the study of quantum effects in mesoscopic
mechanical systems.
