  Development of acoustic and optoacoustic on-chip technologies calls for new
solutions to guiding, storing and interfacing acoustic and optical waves in
integrated silicon-on-insulator (SOI) systems. One of the biggest challenges in
this field is to suppress the radiative dissipation of the propagating acoustic
waves, while co-localizing the optical and acoustic fields in the same region
of an integrated waveguide. Here we address this problem by introducing
Anti-Resonant Reflecting Acoustic Waveguides (ARRAWs) -- mechanical analogues
of the Anti-Resonant Reflecting Optical Waveguides (ARROWs). We discuss the
principles of anti-resonant guidance and establish guidelines for designing
efficient ARRAWs. Finally, we demonstrate examples of the simplest
silicon/silica ARRAW platforms that can simultaneously serve as near-IR optical
waveguides, and support strong backward Brillouin scattering.
