Influences of internal stress in the dynamic behavior of integrated photonic ultrasound transducers

Abstract

Integrated photonic ultrasound transducers (IPUTs) are compact, high-sensitivity devices that combine mechanical sensing with optical readout using integrated photonics. IPUTs typically consist of optical waveguides integrated on a thin mechanical plate that serves as the acoustic sensing element. In many realizations, this plate is formed from thermally oxidized silicon dioxide layers commonly used in photonic fabrication processes. The oxidation process introduces significant residual compressive stress–typically between 200 MPa and 400 MPa–as the structure cools to room temperature. Such stresses can strongly influence the dynamic response of the plate through their contribution to the geometric stiffness of the structure. In this work, the influence of internal stress on the resonance frequency and receive transfer function (RTF) of IPUTs is investigated. Finite element models incorporating residual stress and geometric nonlinearity are developed and validated against experimental measurements and results reported in the literature. Parametric analysis shows that increasing compressive stress progressively reduces the resonance frequency while enhancing the RTF as the structure approaches the critical buckling condition. Beyond this point, changes in the prestressed equilibrium configuration lead to transitions in the dominant vibration mode, producing abrupt variations in the resonance frequency and RTF. These results highlight the importance of accounting for residual stress in the design and analysis of IPUTs and similar plate-based acoustic sensors to ensure reliable dynamic performance and predictable sensitivity.