Distributed salinity sensor based on optical frequency domain reflectometry with polyimide coated single mode fiber

Area of Science:

• Photonics and Sensor Technology
• Materials Science
• Environmental Monitoring

Background:

• Accurate salinity measurement is crucial for oceanographic research and environmental monitoring.
• Existing salinity sensors may face limitations in sensitivity, response time, or applicability in diverse conditions.
• Distributed optical fiber sensing offers a promising platform for developing robust and sensitive measurement tools.

Purpose of the Study:

• To propose and analyze a novel distributed optical fiber sensor for salinity sensing.
• To investigate the performance characteristics of polyimide-coated optical fibers for salinity detection.
• To evaluate the sensor's sensitivity, response time, and measurement uncertainty.

Main Methods:

• Fabrication of single-mode optical fibers coated with polyimide films of varying thicknesses.
• Utilizing optical frequency domain reflectometry (OFDR) for sensing.
• Correlating spectral frequency shifts with changes in external solution salinity.
• Characterizing sensor performance across a salinity range of 0 mol/L to 3.09 mol/L.

Main Results:

• Polyimide coating thickness significantly influences sensor sensitivity.
• Achieved sensitivities ranged from -21.71 GHz/(mol/L) to -42.78 GHz/(mol/L) for coating thicknesses between 126 µm and 249 µm.
• The sensor demonstrated a minimum salinity measurement uncertainty of 0.05 mol/L.
• Polyimide film expansion/shrinkage due to salinity changes was effectively converted to measurable frequency shifts.

Conclusions:

• The developed distributed optical fiber sensor exhibits high sensitivity and accuracy for salinity measurements.
• The polyimide coating's responsiveness to salinity changes is key to the sensor's functionality.
• This technology holds significant potential for real-time ocean parameter observation and ion chemical sensing.