  Opto-mechanical interactions in planar photonic integrated circuits draw
great interest in basic research and applications. However, opto-mechanics is
practically absent in the most technologically significant photonics platform:
silicon on insulator. Previous demonstrations required the under-etching and
suspension of silicon structures. Here we present surface acoustic
wave-photonic devices in silicon on insulator, up to 8 GHz frequency. Surface
waves are launched through absorption of modulated pump light in metallic
gratings and thermoelastic expansion. The surface waves are detected through
photo-elastic modulation of an optical probe in standard race-track resonators.
Devices do not involve piezo-electric actuation, suspension of waveguides or
hybrid material integration. Wavelength conversion of incident microwave
signals and acoustic true time delays up to 40 ns are demonstrated on-chip.
Lastly, discrete-time microwave-photonic filters with up to six taps and 20 MHz
wide passbands are realized using acoustic delays. The concept is suitable for
integrated microwave-photonics signal processing
