An Integrated Fiber Optic Sensor Capable of Simultaneously Measuring of Salinity, Pressure, and Temperature

Compared to single-parameter and dual-parameter sensors, the design of multi-parameter sensors is generally more complex. As a result, finding ways to enhance sensor integration, eliminate cross-sensitivity between channels, and reduce the difficulty of demodulation has always been a challenging issue. In this research, we propose and demonstrate an integrated fiber optic sensor for the measurement of seawater parameters, employing a hybrid structure consisting of seven core fiber (SCF), a femtosecond-drilled hollow core fiber (HCF), a single-mode fiber (SMF), and a multi-mode fiber (MMF). The proposed sensor comprises three channels: a salinity measurement channel based on surface plasmon resonance (SPR), a pressure measurement channel based on Fabry-Perot interferometry (FPI), and a temperature measurement channel based on fiber Bragg grating (FBG). According to the experimental results, the sensor exhibits sensitivities of 0.37 nm/‰ for salinity, −9.72 nm/MPa for pressure, and −0.83 nm/°C for temperature. The integration of three different sensing mechanisms, along with space division multiplexing technology, in the proposed sensor effectively resolves the challenges of spectral overlap between channels and the demodulation complexities encountered in previous studies. This innovative solution enables accurate and reliable measurement results for each parameter without interference from other channels. With its advantages of multi-functionality, low crosstalk, ease of demodulation, compact structure, and cost-effectiveness, the proposed sensor can not only provide accurate basic data for ocean detection but also provide necessary compensation for the measurement of physical, geographical, chemical, and biological parameters of the ocean.