Push-Pull acousto-optic modulator based on non-suspended thin-film lithium niobate on silicon substrate

Abstract: Acousto-optic modulators (AOMs) are particularly attractive for microwave-to-optical conversion, quantum transduction, and optical frequency manipulation. For these applications, chip-scale AOMs that combine high efficiency, broad bandwidth, and low optical loss are highly desirable. Although suspended and resonant AOMs can enhance modulation efficiency, they typically suffer from stability concerns and limited bandwidth. Here, we demonstrate a non-suspended built-in push-pull AOM on a thin-film lithium niobate (TFLN) on silicon substrate that simultaneously offers high efficiency and relatively broad bandwidth. We further investigate the orientation dependence of electromechanical coupling in X-cut TFLN by fabricating devices with different acoustic propagation directions and identify an optimized orientation for enhanced acousto-optic transduction. Our low-loss device achieves a half-wave voltage-length product of 1.004 V cm at 0.842 GHz with an interaction length of 400 micrometers, together with a relatively wide acousto-optic modulation bandwidth of 132.5 MHz. These results pave the way for efficient, practical integrated photonic-phononic links.