Crystals that can confine both light and mechanical vibrations.
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.
References
Eichenfield, M., Chan, J., Camacho, R. M., Vahala, K. J. & Oskar, P. Optomechanical crystals. Nature 10.1038/nature08524 (2009).
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Vaughan, O. Coupled waves. Nature Nanotech (2009). https://doi.org/10.1038/nnano.2009.344
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DOI: https://doi.org/10.1038/nnano.2009.344