  By harnessing the resonant nature of localized electromagnetic modes in a
nanostructured silicon membrane, an all-dielectric metamaterial can act as
nonlinear medium at optical telecommunications wavelengths. We show that such
metamaterials provide extremely large optomechanical nonlinearities, operating
at intensities of only a few {\mu}W per unit cell and modulation frequencies as
high as 152 MHz, thereby offering a path to fast, compact and energy efficient
all-optical metadevices.
