Multimode fibre tapers based in-line Mach–Zehnder fibre-optic interferometer for curvature and vibration sensing

This paper introduces an in-line Mach–Zehnder fibre-optic interferometer (IMZI) based on two multimode fibre tapers for high-precision curvature and vibration detection. The IMZI was formed by fusing the structure of multimode fibre taper (MFT)-single-mode fibre (SMF)–MFT. By inducing non-adiabatic tapering in the multimode fibre (MMF), the cladding modes of the MMF were excited effectively, which in turn stimulate high-order cladding modes within the SMF, substantially enhancing the sensitivity of the fibre sensor. In curvature sensing experiments, the sensor demonstrated an exceptionally high intensity sensitivity of approximately 97.5 dB/m−1 and a wavelength sensitivity of roughly −24.2 nm/m−1. When affixed to a cantilever beam, the IMZI proved to be effective for vibration measurements, offering a sensitivity of 23.27 mV/nm and a signal-to-noise ratio (SNR) of 50 dB at 1000 Hz.