Underwater fiber-optic salinity and pressure sensor based on surface plasmon resonance and multimode interference

Area of Science:

• Photonics and Sensor Technology
• Oceanographic Instrumentation
• Applied Physics

Background:

• Accurate underwater environmental monitoring requires advanced sensing technologies.
• Simultaneous measurement of multiple parameters like salinity and pressure is crucial for oceanographic studies.
• Existing sensors may face limitations in sensitivity, selectivity, or multiplexing capabilities.

Purpose of the Study:

• To develop and demonstrate a novel fiber-optic sensor for simultaneous measurement of salinity and pressure.
• To leverage surface plasmon resonance (SPR) and multimode interference (MMI) phenomena for enhanced sensing performance.
• To provide a robust and efficient solution for underwater ocean detection.

Main Methods:

• Fabrication of a single-mode-multimode-single-mode-multimode-single-mode fiber structure.
• Deposition of a gold film on the fiber for surface plasmon resonance (SPR) excitation.
• Integration of the fiber structure with an elastic cylinder to form a sensing head.
• Utilizing the SPR region for salinity measurement and the MMI region for pressure measurement.
• Simulation of the multimode interference (MMI) spectrum using the finite-difference beam propagation method.

Main Results:

• Achieved a sensitivity of 0.36 nm/‰ for salinity measurement.
• Achieved a sensitivity of -1.42 nm/MPa for pressure measurement.
• Demonstrated insignificant crosstalk between salinity and pressure measurements.
• Experimental validation of the sensor's performance for simultaneous detection.

Conclusions:

• The developed SPR-MMI fiber-optic sensor enables simultaneous and accurate measurement of salinity and pressure.
• This technology offers a promising new method for ocean detection and environmental monitoring.
• The study highlights the potential of integrated SPR-MMI sensors for various applications.