Multi-layer, offset-coupled sapphire fiber Bragg gratings for high-temperature measurements

Area of Science:

• Materials Science and Engineering
• Optical Physics
• Sensor Technology

Background:

• Sapphire fiber Bragg gratings (SFBGs) are crucial for high-temperature sensing.
• Existing SFBGs have limitations in reflectivity and mode control.
• Advanced fabrication techniques are needed to enhance SFBG performance.

Purpose of the Study:

• To fabricate and characterize multi-layer SFBGs using a femtosecond laser.
• To investigate the impact of layer quantity and spacing on SFBG reflectivity and spectral properties.
• To evaluate the high-temperature performance and sensing capabilities of the developed SFBGs.

Main Methods:

• Femtosecond laser line-by-line scanning technique for multi-layer SFBG fabrication.
• Spectral analysis of SFBGs with varying layer configurations.
• Offset coupling for higher-order mode suppression.
• High-temperature testing to determine thermal response and sensitivity.

Main Results:

• Multi-layer SFBG structure significantly increases reflectivity (e.g., 34.1% for double-layer vs. 6.3% for single-layer).
• Offset coupling effectively suppresses higher-order modes, reducing bandwidth to 1.32 nm (FWHM).
• SFBGs demonstrate excellent high-temperature stability up to 1612°C with a sensitivity of 45.2 pm/°C.

Conclusions:

• Multi-layer SFBG fabrication via femtosecond laser offers enhanced reflectivity and mode control.
• The developed SFBGs exhibit robust performance at extreme temperatures.
• These multi-layer SFBGs are suitable for high-temperature sensing in demanding industrial sectors.