Electrically driven acousto-optic devices that provide beam deflection and
optical frequency shifting have broad applications from pulse synthesis to
heterodyne detection. Commercially available acousto-optic modulators are based
on bulk materials and consume Watts of radio frequency power. Here, we
demonstrate an integrated 3-GHz acousto-optic frequency shifter on thin-film
lithium niobate, featuring a carrier suppression over 30 dB. Further, we
demonstrate a gigahertz-spaced optical frequency comb featuring more than 200
lines over a 0.6-THz optical bandwidth by recirculating the light in an active
frequency shifting loop. Our integrated acousto-optic platform leads to the
development of on-chip optical routing, isolation, and microwave signal
processing
