Efficient and Nonsuspended Acousto-Optic Mach–Zehnder Modulators on Silicon Photonic Platform

Acousto-optic (AO) modulation offers a unique mechanism to bridge the microwave and optical domain, enabling key AO functionalities in optical communications and quantum information processing. However, the conventional implementation of AO modulation on piezoelectric platforms impedes the development of scalable photonic integrated circuits. Here, nonsuspended AO Mach–Zehnder modulators with push–pull configurations are demonstrated on a standard silicon-on-insulator platform through heterogeneous integration of piezoelectric scandium-doped aluminum nitride (Al0.6Sc0.4N). Surface acoustic waves are generated by interdigital transducers (IDTs) patterned on the AlScN film, modulating the optical waves confined in the silicon waveguides without introducing additional optical losses caused by the AlScN film. By engineering multiple AO-active segments in spiral-like waveguide arms, the proposed modulators achieve a 12.32 dB enhancement in modulation efficiency with seven AO-active segments compared with a single segment. Additionally, by incorporating an acoustic reflector in the IDTs, the modulators achieve a high electromechanical coupling coefficient of 1.36%, a 1.12 dB enhancement in modulation efficiency, and a record-low half-wave voltage-length product of 0.10 V cm with nine AO-active segments, enabling efficient microwave-to-optical conversion. These AO modulators are fully compatible with complementary metal-oxide-semiconductor (CMOS) technology, demonstrating high efficiency, robustness, and scalability for photonic integrated circuits.