A highly sensitive strain sensing scheme based on harmonic Vernier effect

Abstract

This paper firstly proposes and experimentally validates a high-sensitivity strain sensing scheme based on the harmonic Vernier effect. The design integrates an in-line Mach-Zehnder interferometer (MZI), constructed from multimode (MM)-ultra-high numerical aperture (UHNA)-multimode fiber, with a Sagnac interferometer (SI) using a PANDA polarization-maintaining fiber (PMF). By matching the free spectral ranges (FSRs) of the MZI and SI, a first-order harmonic Vernier effect is achieved, yielding a substantial enhancement in strain sensitivity. Simulations of the superimposed spectra reveal that appropriate parameter selection reduces the full width at half maximum (FWHM) of the Vernier envelope and maximizes the amplification factor without compromising the quality factor (Q-factor ). To further improve performance, fast Fourier transform (FFT) analysis is applied for frequency-domain filtering and noise suppression. Experimental results confirm that the proposed scheme achieves a strain sensitivity of 119.6 pm/με, improving strain sensitivity by more than 20 times compared with a single SI, while maintaining minimal hysteresis. The scheme features high sensitivity, low cost, a simple and flexible structure, and minimal hysteresis, making it a promising solution for strain sensing applications.