Line-by-line type-X FBGs with high-temperature stability and low loss.

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Fiber Optic Sensors

Background:

• Traditional fiber Bragg gratings (FBGs) face limitations in high-temperature applications due to degradation.
• Type-II FBGs offer stability but suffer from higher losses.
• Developing FBGs with both high-temperature stability and low loss is crucial for advanced sensing.

Purpose of the Study:

• To present a novel method for inscribing high-temperature stable, low-loss Type-X fiber Bragg gratings.
• To investigate the effects of overwriting and grating order on Type-X FBG formation and performance.
• To demonstrate the thermal stability of the fabricated Type-X FBGs.

Main Methods:

• Inscribing Type-X FBGs line-by-line using a controlled laser energy approach.
• Examining the impact of overwriting grating planes and varying grating orders (m > 2).
• Fabricating arrays of gratings and conducting isochronal annealing experiments up to >1000 °C.

Main Results:

• A method was established to produce Type-X FBGs with Type-I modification profiles and Type-II stability, avoiding Type-II losses.
• Optimal inscription parameters identified: single scan per plane at maximum energy before damage, with grating orders m > 2.
• Fabricated Type-X FBGs demonstrated high-temperature stability exceeding 1000 °C.

Conclusions:

• The developed method enables the fabrication of low-loss, high-temperature stable Type-X FBGs.
• Understanding inscription parameters like energy, overwriting, and grating order is key to optimizing Type-X FBG performance.
• Type-X FBGs represent a significant advancement for high-temperature fiber optic sensing applications.