High‐Efficiency Michelson‐Interferometric Intramodal Acousto‐Optic Modulation Enabled by Surface Acoustic Wave Confinement

ABSTRACT Integrated acousto‐optic modulators support microwave photonics and optical signal processing. However, efficient intramodal modulation remains challenging owing to weak photon–phonon interactions and limited effective interaction lengths. Herein, a Michelson‐interferometer‐based intramodal acousto‐optic modulator on a thin‐film lithium niobate‐chalcogenide glass platform is demonstrated. In this device, the acoustic velocity mismatch between chalcogenide glass and lithium niobate promotes the confinement of surface acoustic waves within the waveguide, greatly enhancing strain in the chalcogenide photonic waveguide. In addition, the push–pull Michelson architecture reuses the optical interaction region via forward and backward propagation. As a result, the fabricated device achieves a normalized coupling coefficient of 87 mm −1 W −1/2 and a first‐order sideband modulation efficiency of 32% with an interaction length of only 200 µm at a drive power of 15 dBm. These results demonstrate a compact approach to highly efficient integrated acousto‐optic phase modulation and provide a promising platform for microwave‐photonic and coherent optical signal processing.