  We report the experimental demonstration of converting coherent optical
fields between two different optical wavelengths by coupling two optical modes
to a mechanical breathing mode in a silica resonator. The experiment is based
on an itinerant approach, in which state-mapping from optical to mechanical and
from mechanical to another optical state takes place simultaneously. In
contrast to conventional nonlinear optical processes, optomechanical impedance
matching as well as efficient optical input-output coupling, instead of
phase-matching, plays a crucial role in optomechanics-based wavelength
conversion.
