High sensitivity all-fiber Michelson interferometer respiratory sensor based on PVA-coated down-taper

This paper first proposes a wearable breathing sensor based on a single-mode fiber (SMF)-down-taper-Panda polarization-maintaining fiber (PMF) structure with a PVA-coated taper for enhanced coupling efficiency and durability. The sensor features a fiber sphere at the PMF end for improved sensitivity, achieving a curvature sensitivity of 34.8508 dB/m^-1, a temperature sensitivity of 0.0034 dB/°C, and a humidity sensitivity of 0.5742 nm/%RH. Tested on five volunteers, it reliably detected respiratory rates (0.21-0.41 Hz) with <8% repeatability error and >0.9 Pearson correlation with commercial sensors. The design offers high sensitivity, comfort, and fast response (1.06 s rise, 1.19 s recovery), making it suitable for healthcare monitoring.