High-Sensitivity Fiber SPR-MZI Salinity Sensor With Temperature Compensation Function

Abstract

This article proposes a high-sensitivity Mach–Zehnder interferometer (MZI)-surface plasmon resonance (SPR) salinity sensor based on a fiber optic macrobending structure of single-mode fiber-multimode fiber-single mode fiber (SMS) to address the issue of temperature-salt cross-sensitivity in seawater detection. By a fast Fourier transform (FFT) and frequency-domain filtering, the sensing signal was separated, and by combining it with a second-order sensitivity matrix, the in situ temperature compensation was realized. Meanwhile, the bending diameter of the macrobending structure is adjusted, thereby adjusting the light incident angle in the sensing area to regulate the salinity detection sensitivity of the sensor. The experiment indicates that the salinity sensitivity of the sensor reaches 1.08832 nm/‰, and the refractive index sensitivity is as high as 5911.06 nm/RIU. This scheme has a minimalist structure, high stability, and does not require complex processing, providing an effective solution for high-precision temperature and salinity synchronous detection in the ocean.