  We demonstrate conversion of up to 4.5 GHz-frequency microwaves to 1500
nm-wavelength light using optomechanical interactions on suspended thin-film
lithium niobate. Our method utilizes an interdigital transducer that drives a
free-standing 100 $\mu$m-long thin-film acoustic resonator to modulate light
travelling in a Mach-Zehnder interferometer or racetrack cavity. Owing to the
strong microwave-to-acoustic coupling offered by the transducer in conjunction
with the strong photoelastic, piezoelectric, and electro-optic effects of
lithium niobate, we achieve a half-wave voltage of $V_\pi$ = 4.6 V and $V_\pi$
= 0.77 V for the Mach-Zehnder interferometer and racetrack resonator,
respectively. The acousto-optic racetrack cavity exhibits an optomechancial
single-photon coupling strength of 1.1 kHz. Our integrated nanophotonic
platform coherently leverages the compelling properties of lithium niobate to
achieve microwave-to-optical transduction. To highlight the versatility of our
system, we also demonstrate a lossless microwave photonic link, which refers to
a 0 dB microwave power transmission over an optical channel.
