Interferometric temperature-insensitive strain measurement with different-diameter fiber Bragg gratings

Area of Science:

• Optoelectronics
• Fiber optic sensing
• Materials science

Background:

• Accurate strain and temperature measurement is crucial for structural health monitoring.
• Existing fiber optic sensors often struggle to differentiate between strain and temperature effects.
• Interferometric techniques offer high sensitivity but require robust signal processing.

Purpose of the Study:

• To develop an interferometric strain-sensing system capable of distinguishing strain from temperature.
• To utilize spliced fiber Bragg gratings with different diameters for enhanced strain-temperature decoupling.
• To propose a novel measurement method based on amplitude variation of the interference signal.

Main Methods:

• An unbalanced Mach-Zehnder wavelength discriminator was combined with spliced fiber Bragg gratings.
• Gratings were fabricated on 135- and 165-micrometer diameter fibers from the same preform.
• The system monitored the amplitude variation of the interference signal to measure the relative Bragg wavelength difference.

Main Results:

• The spliced gratings exhibited similar temperature sensitivities but distinct responses to strain.
• The relative Bragg wavelength difference was found to be solely dependent on strain.
• Accurate strain measurement was achieved by monitoring amplitude variations, decoupling it from temperature influences.

Conclusions:

• The proposed system effectively distinguishes strain from temperature effects in fiber optic sensing.
• The use of spliced different-diameter fiber Bragg gratings provides a robust solution for strain-only measurement.
• Monitoring amplitude variation offers an alternative to conventional phase variation for accurate strain sensing.