Unveiling Efficient Acousto-Optic Modulation in Silicon Photonic Devices via Lithium Niobate Using Transfer Printing.

Piezo-optomechanics presents a promising route to convert microwave signals to the optical domain, implementing processing tasks that are challenging using conventional electronics. The surge of integrated photonics facilitates the exploitation of localized light-sound interactions toward new technological paradigms. However, efficient acousto-optic interaction has yet to be fully exploited in silicon due to the absence of piezoelectricity, despite its maturity in photonic integrated circuits. Here, we introduce a distinctive acousto-optic scheme to supplement silicon photonic devices through heterogeneous integration with lithium niobate (LN). Utilizing LN as an efficient acoustic pump to harness the inherently exceptional photoelasticity in silicon, we demonstrate efficient microwave-to-acoustic transduction, ultimately achieving a modulation figure-of-merit of ∼ 0.496 V·cm. This efficient modulation scheme is further extended to implement non-reciprocal intermodal modulation. The proposed hybrid integration route opens new possibilities for tailoring photon-phonon interactions in silicon, consolidating acousto-optic technology in multifunctional integrated photonics.