Piezoelectrically coupling surface acoustic waves to silicon waveguides.

The coupling of surface acoustic waves (SAWs) with optical waveguides through piezoelectric films is an emerging method of connecting microwave and optical domains. In this work, we demonstrate the intramodal and intermodal acousto-optic modulation in silicon waveguides by electrically driving interdigital transducers on CMOS-compatible piezoelectric AlScN film. The proposed intramodal acousto-optic phase modulation is significant enhanced by 16.72 dB in the fabricated spiral waveguide with five interaction segments over a broad range of optical wavelengths, and demonstrates the ability to perform microwave photonic filtering. In addition, the proposed intermodal acousto-optic modulation exhibits single-sideband phase modulation with high single-sideband contrast (> 30 dB) and a wide optical bandwidth of 68 nm, which is capable of acousto-optic frequency shift and optical mode conversion, providing an insightful idea for nonreciprocal optical propagation.