Multimodal speckle and polarization fiber sensing for localized, broadband vibration monitoring

High-bandwidth and multi-point acoustic and vibration sensing is a critical asset for real-time condition monitoring, maintenance, and surveillance applications. In the case of large scales and harsh environments, optical fiber distributed sensing has emerged as a compelling alternative to electronic transducers, featuring lower installation and maintenance costs, along with compact footprints and enhanced robustness. Yet, current distributed fiber-optic sensing solutions are typically costly and face a resolution-bandwidth tradeoff. This work addresses the current challenges of distributed fiber optic sensors by presenting a dual-modality architecture that combines speckle dynamic analysis and polarization interrogation. The implementation operates under a single-active-source assumption across four discrete points distributed on a 4-m length fiber and uses camera-based speckle analysis to localize the active position, while the polarization interrogation reconstructs the corresponding waveform from 100 Hz to 40 kHz with a 200 kHz acquisition rate, with 35 dB SNR. Overall, the work establishes a general and promising blueprint to harness multimodality in fiber sensing and break single-modality constraints.