An SPR-MZ Interference-Based Fiber-Optic Sensor for Dual-Parameter Measurement of Seawater Temperature and Salinity

This study introduces a novel single-hole, dual-core suspended fiber optic sensor that integrates the surface plasmon resonance (SPR) effect and the Mach-Zehnder (MZ) interference principle, enabling the simultaneous monitoring of both salinity and temperature in seawater. The sensor comprises of two segments of multimode fiber (MMF) and a segment of single-hole dual-core suspended fiber (SHTSCF), where the surface-sputtered gold film (Au) on the SHTSCF segment excites the SPR effect for salinity detection; while the MMF and SHTSCF segments together form an MZ interference structure for temperature detection, effectively solving the crosstalk problem between salinity and temperature measurements. The experimental findings reveal that the sensor exhibits a salinity sensitivity of 0.5186 nm/‰ within the salinity bracket of 5 to 40‰, and a temperature sensitivity of 0.1263 nm/℃ across the temperature spectrum of 5 to 50 °C. The maximum temperature and salinity fluctuations caused by the sensor under different temperature and salinity conditions are 3.2 °C and 1.38 ‰ respectively, indicating that it has good stability. Moreover, a crosstalk effect of -0.149 nm/°C is observed between temperature and salinity measurements. This SPR sensor demonstrates excellent stability, repeatability, and reliability, with a compact structure, providing a new technological pathway for the synchronous monitoring of dual parameters in seawater.