Vectorial optomechanical sensing: controlling coherent coupling in an engineered fiber resonator

In precision optomechanical sensing, polarization instability is typically regarded as a fundamental noise source that must be suppressed, posing a basic limitation to the conventional sensing paradigm. This work extends this paradigm by demonstrating the active control and coherent utilization of polarization as a distinct sensing channel for signal enhancement. We introduce “vectorial optomechanical sensing,” the approach that transforms this polarization “noise” into a valuable signal. This is achieved using an engineered planar dual-spiral optical fiber resonator that deterministically partitions a single mechanical strain into two orthogonal modes: frequency and polarization. A crucial control experiment directly validates the engineered nature of this effect, showing a strong, tunable polarization dependence that is absent in conventional single-loop designs. A nonideal physical model incorporating a minor phase offset excellently describes the experimental data, revealing a realistic sensitivity enhancement of over 188%. The optimized sensor achieves a sensitivity of 557.82 mV/Pa, a signal-to-noise ratio of 24.8 dB, and a noise-equivalent pressure of 2.45 mPa/Hz. Notably, we demonstrate a sensing bandwidth extending to 3 kHz under Pound–Drever–Hall (PDH) interrogation, overcoming the conventional low-frequency limitation of such resonant systems. Its high-fidelity signal capture capability is demonstrated by monitoring ballistocardiogram (BCG) signals with gold-standard validation and achieving high-accuracy classification of human speech. This principle of engineering coherent interplay between orthogonal modes offers a universal pathway for surpassing the conventional performance limits of diverse high-Q resonant systems.