Direct period measurement for fiber Bragg grating using an optical imaging technique

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Metrology

Background:

• Fiber Bragg gratings (FBGs) are crucial optical components in sensing and telecommunications.
• Accurate measurement of FBG grating periods is essential for device performance.
• Existing measurement techniques may lack simplicity or directness.

Purpose of the Study:

• To propose and validate a novel optical imaging approach for measuring FBG periods.
• To demonstrate the efficacy of differential interface contrast (DIC) microscopy for FBG analysis.
• To establish a reliable method for characterizing FBGs with varying grating periods.

Main Methods:

• Utilized a differential interface contrast (DIC) microscope coupled with a high-resolution CCD camera.
• Employed image processing techniques on captured microscope images to extract grating profiles.
• Fabricated FBGs with varying periods by prestraining photosensitive fibers during UV-writing.

Main Results:

• Achieved low-noise grating profiles and accurate determination of grating periods.
• Demonstrated that a large image sample size in processing reduces measurement uncertainty.
• Observed excellent linearity between measured Bragg wavelengths and grating periods.
• Validated the measured strain-optics coefficient against literature values.

Conclusions:

• The proposed DIC microscopy technique provides a simple and direct method for FBG period measurement.
• The approach is capable of accurate characterization of FBGs with different grating periods.
• This technique contributes to reliable FBG fabrication and characterization in optical sensing applications.