How to splice a temperature-sensing fiber optic grating

Splicing a temperature-sensing Fiber Bragg Grating (FBG) requires careful alignment, proper fiber preparation, and controlled fusion to preserve the grating's reflection properties and temperature sensitivity.

Understanding the FBG

A Fiber Bragg Grating is a segment of optical fiber with a periodic modulation of the refractive index in the core, which reflects a specific Bragg wavelength while transmitting other wavelengths . The Bragg wavelength shifts with temperature due to the thermo-optic effect and thermal expansion of the fiber . Maintaining the integrity of this grating during splicing is critical to ensure accurate temperature measurements.

Preparation Steps

1. Fiber Cleaning and Stripping: Remove the protective coating from the fiber ends using a fiber stripper, exposing the bare glass. Clean the fiber with isopropyl alcohol to remove any debris or oils.
2. Cleaving: Use a high-precision fiber cleaver to create a flat, perpendicular end face. A clean cleave minimizes insertion loss and reflection at the splice point.
3. Handling the Grating: Avoid mechanical stress or bending near the FBG region, as strain can shift the Bragg wavelength and affect temperature readings .

Splicing Techniques

1. Fusion Splicing:
   • Align the fiber cores precisely using a fusion splicer.
   • Apply a controlled electric arc to fuse the fibers together.
   • Ensure the arc parameters are optimized to prevent thermal damage to the grating, which could alter the refractive index modulation.
   • Some splicers have low-heat or specialty FBG modes to minimize grating degradation.
2. Mechanical Splicing (Alternative):
   • Use a mechanical splice sleeve to align the fibers.
   • This method avoids heating but may introduce slightly higher insertion loss.
   • Suitable for temporary or field applications where fusion splicing is not feasible.

Post-Splice Considerations

• Test the Bragg Wavelength: After splicing, measure the reflected spectrum to ensure the Bragg wavelength has not shifted significantly.
• Strain Relief: Protect the splice with a sleeve or buffer to prevent mechanical stress.
• Temperature Calibration: Verify the FBG's temperature response post-splice to ensure accurate sensing .

Tips for Reliable Splicing

• Use single-mode fibers compatible with the FBG.
• Avoid splicing directly within the grating region; splice outside the FBG to preserve its structure.
• Minimize bending and tension during handling.
• If multiple FBGs are multiplexed, maintain proper spacing to prevent cross-talk. By following these steps, you can successfully splice a temperature-sensing FBG while maintaining its reflection characteristics and temperature sensitivity, ensuring reliable performance in sensing applications .