  We demonstrate optomechanically-mediated electromagnetically-induced
transparency and wavelength conversion in silicon nitride (Si3N4) microdisk
resonators. Fabricated devices support whispering gallery optical modes with a
quality factor (Q) of 10^6, and radial breathing mechanical modes with a Q=10^4
and a resonance frequency of 625 MHz, so that the system is in the resolved
sideband regime. Placing a strong optical control field on the red (blue)
detuned sideband of the optical mode produces coherent interference with a
resonant probe beam, inducing a transparency (absorption) window for the probe.
This is observed for multiple optical modes of the device, all of which couple
to the same mechanical mode, and which can be widely separated in wavelength
due to the large bandgap of Si3N4. These properties are exploited to
demonstrate frequency upconversion and downconversion of optical signals
between the 1300 nm and 980 nm bands with a frequency span of 69.4 THz.
