This study reports the fabrication of an 4th-order line-by-line Fiber Bragg Gratings (FBG) array using femtosecond laser inscription within a highly multimode coreless optical fiber, with a particular focus on achieving substantial multiplexing capabilities. An ultra-fast annealing procedure is employed, resulting in an impressive enhancement of the FBG sensor's fringe visibility by approximately 13 dB, signifying a notable improvement of approximately ~4 dB. This substantial enhancement contributes to the long-term stability and performance of the multiplexed FBG array in extreme temperature conditions. The systematic fabrication approach employed for the multiplexed FBG array guarantees a high signal-to-noise ratio (SNR) for each individual FBG within the array. This FBG array is intended for extreme temperature applications, addressing limitations associated with traditional FBGs based on doped optical fibers, including SNR degradation and temperature-induced fringe drift. Testing at temperatures up to 1120°C demonstrates the FBG array's stability without fluctuations in readings. Furthermore, it endures seven heat cycles, spanning from 500°C to 1120°C, over 60 hours, exhibiting outstanding thermal stability. This highly multiplexed FBG array with an ultra-fast annealing approach holds promise for extreme temperature environments, such as steelmaking, where precise and reliable distributed temperature monitoring is imperative.


Electrical and Computer Engineering

Second Department

Materials Science and Engineering

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Article - Preprint

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