Highly sensitive in-fiber interferometric refractometer with temperature and axial strain compensation

Area of Science:

• Optoelectronics
• Fiber Optics Sensing
• Interferometry

Background:

• Accurate measurement of refractive index (RI) is crucial in various scientific and industrial applications.
• Environmental factors like temperature and axial strain can interfere with RI measurements, necessitating compensation strategies.
• Mach-Zehnder interferometers (MZIs) offer high sensitivity but require robust designs for practical sensing.

Purpose of the Study:

• To propose and demonstrate a novel fiber-optic refractometer capable of simultaneous measurement of refractive index, temperature, and axial strain.
• To achieve temperature- and axial strain-compensated refractive index measurement.
• To leverage highly sensitive outer-cladding modes in a tapered bend-insensitive fiber based MZI.

Main Methods:

• Utilizing a tapered bend-insensitive fiber to construct a Mach-Zehnder interferometer.
• Employing highly sensitive outer-cladding modes for sensing.
• Calibrating peak wavelength shifts to form a wavelength-related character matrix (λ)M(RI,T,ε).
• Acquiring a phase-related character matrix (Φ)M(RI,T,ε) through direct determination of phase shifts.

Main Results:

• Demonstration of a fiber-optic refractometer with simultaneous multi-variable sensing capabilities.
• Successful compensation for temperature and axial strain effects on refractive index measurements.
• Development of wavelength- and phase-related characterization matrices for comprehensive environmental sensing.

Conclusions:

• The proposed fiber-optic refractometer effectively measures refractive index while compensating for temperature and axial strain.
• The use of outer-cladding modes in a tapered bend-insensitive fiber MZI provides a sensitive platform for simultaneous environmental sensing.
• The developed characterization matrices enable accurate and simultaneous determination of multiple variables (RI, T, ε).