First demonstration of acousto-optic modulation on thin-film lithium tantalate

Realization of efficient acousto-optic modulation on a chip is important for the development of photonic integrated circuits. While thin-film lithium niobate has been considered as an ideal platform for this purpose, recent studies have shown that its large birefringence, strong photorefraction, and slow relaxation of electro-optic response may limit its applications in high-speed optical communication. Lithium tantalate, another piezoelectric material with an even wider transparency window, emerges as a competing candidate for photonic integrated circuits because of its smaller birefringence, weaker photorefraction, and faster relaxation of electro-optic response. Here, by adopting the mechanism of bound states in the continuum for ultralow-loss waveguiding, we demonstrate for the first time acousto-optic modulation on thin-film lithium tantalate. The VπL is measured to be as low as 0.107 (0.047) V cm for the fundamental (first-order) Rayleigh acoustic mode at 0.626 (1.104) GHz, outperforming most of their counterparts on the lithium niobate platforms. Our work establishes a direct link between optical and microwave photons on thin-film lithium tantalate and paves the way for on-chip applications of acoustic sensors, lasers, isolators, and filters.