Co-localized optical and acoustic defect modes enable resonantly enhanced photoelastic readout in a one-dimensional phoxonic multilayer

Efficient acousto-optic transduction in compact multilayer platforms requires the coexistence of a spectrally confined optical resonance and a mechanically responsive acoustic mode with strong spatial and spectral overlap. In this work, a shared-geometry one-dimensional phoxonic multilayer is numerically investigated for enhanced photoelastic readout through defect-mediated optical–acoustic coupling. The proposed architecture consists of a responsive central defect layer embedded between reversed periodic bilayers, with optical and longitudinal acoustic characteristics modeled using transfer-matrix formulations. Candidate structures are screened based on the formation of localized defect states within the corresponding optical and acoustic Bloch stop bands, while a first-order photoelastic model is applied to quantify the conversion of acoustic strain into optical resonance modulation. The optimized configuration, consisting of five bilayers on each side of a 494.13 nm defect layer, supports an optical defect resonance at 1521.83 nm with a quality factor of 1.51 × 104 and an acoustic defect mode at 3.22425 GHz with a quality factor of 833.2. The predicted displacement sensitivity reaches 2.724 pm/nm, corresponding to a strain sensitivity of 0.409 pm/µε. Field-energy analysis demonstrates simultaneous localization of optical and acoustic modes within the defect cavity, while frequency-domain calculations reveal a 21.67-fold enhancement of the first-order photoelastic response when the acoustic excitation is resonantly matched to the defect mode. Further assessments, including defect-free reference structures, deterministic thickness perturbations, passive-loss evaluations, and Monte Carlo parameter analysis, characterize resonance robustness, fabrication-related variability, and the consistency of the proposed transduction mechanism. These results establish a calibration-aware numerical framework for designing compact one-dimensional phoxonic structures with enhanced defect-assisted acousto-optic readout capabilities.