  Whispering gallery modes (WGMs), circulating modes near the surface of a
spheroidal material, have been known to exhibit high quality factors for both
acoustic and electromagnetic waves. Here, we report an electro-optomechanical
system, where the overlapping WGMs of acoustic and optical waves along the
equator of a dielectric sphere strongly couple to each other. The
triple-resonance phase-matching condition provides a large enhancement of the
Brillouin scattering only in a single sideband, and conversion from the input
radio-frequency signal exciting the acoustic mode to the output optical signal
is observed.
