Credit: © 2009 NPG

Photonic crystals are structures patterned with a periodicity in dielectric constant and can manipulate the properties of photons. Such materials have a photonic bandgap — a range of frequencies for which light cannot propagate through the crystal — and they have been engineered to disperse, guide and trap light. Phononic crystals are periodic structures that use analogous ideas to manipulate mechanical vibrations, and such materials have a phononic bandgap — a range of frequencies for which phonons cannot propagate through the crystal.

Oskar Painter and colleagues at the California Institute of Technology have now created optomechanical crystals — planar circuits that act as both photonic and phononic crystals1. The structures allow light and mechanical vibrations to be controlled and confined to a small space, providing enhanced photon–phonon interactions.

The researchers fabricated a silicon-on-insulator microchip, which had an etched silicon nanobeam with rectangular holes formed by thin cross-bars connected on both sides to thin rails. The translational symmetry of the patterned beam was deliberately disrupted by a 'defect' — a decrease in the lattice constant of the beam. The structure allowed the simultaneous localization and coupling of 200-terahertz photons and 2-gigahertz phonons.

The California team expect that their planar optomechanical crystals could provide new opportunities in signal processing for photonics and electronics applications, and could lead to ultrasensitive mass sensors.