Ultrasensitive fiber-optic Vernier salinometer based on an integrated dual-microcavity interferometer

Area of Science:

• Photonics and Sensor Technology
• Marine Science Instrumentation
• Optical Fiber Sensing

Background:

• Accurate salinity measurement is crucial for understanding oceanographic processes and climate change.
• Existing methods for salinity detection can be complex or lack the required sensitivity.
• Integrated optical fiber sensors offer potential for compact, high-performance sensing solutions.

Purpose of the Study:

• To report a novel integrated optical fiber Vernier sensor for ultra-sensitive salinity measurement.
• To demonstrate the sensor's performance characteristics, including sensitivity, resolution, and temperature cross-sensitivity.
• To highlight the sensor's potential for practical marine environment monitoring.

Main Methods:

• Fabrication of a no-core-hollow-core-no-core (NCF-HCF-NCF) fiber structure within a millimeter-length open-cavity.
• Utilizing the Vernier effect by precisely adjusting optical path differences for enhanced sensitivity.
• Systematic experimental testing to evaluate salinity and temperature responses.

Main Results:

• Achieved a high magnification factor of 8.33.
• Demonstrated a salinity sensitivity of 18.43 nm/‰, with a resolution of 0.0032‰.
• Observed a temperature sensitivity of -10.25 nm/℃, with measurement errors constrained to 1.9%.

Conclusions:

• The proposed integrated optical fiber Vernier sensor enables ultra-sensitive salinity measurements.
• The sensor exhibits high resolution, good accuracy, and simple fabrication.
• This cost-effective sensor is highly promising for high-accuracy marine environment monitoring.