Falak, Przemyslaw, Lee, Timothy, Zahertar, Shahrzad, Shi, Bo, Moog, Bruno, Brambilla, Gilberto, Holmes, Christopher and Beresna, Martynas (2023) Compact high-resolution FBG strain interrogator based on laser-written 3D scattering structure in flat optical fiber. Scientific Reports, 13 (1), 1-11, [8805 (2023)]. (doi:10.1038/s41598-023-35708-1).
Abstract
We demonstrate a fiber Bragg grating (FBG) strain interrogator based on a scattering medium to generate stable and deterministic speckle patterns, calibrated with applied strain, which are highly dependent on the FBG back-reflection spectral components.
The strong wavelength-dependency of speckle patterns was previously used for high resolution wavemeters where scattering effectively folds the optical path, but instability makes practical realization of such devices difficult. Here, a new approach is demonstrated by utilizing femtosecond laser-written scatterers inside flat optical fiber, to enhance mechanical stability. By inscribing 15 planes of pseudo-randomized nanovoids (714 × 500 voids per plane) as a 3D array in a 1 × 0.7 × 0.16 mm volume, the intrinsic stability and compactness of the device was improved. Operating as a wavemeter, it remained stable for at least 60 hours with 45 pm resolution over the wavelength range of 1040-1056 nm. As a reflection mode FBG interrogator, after calibrating speckle patterns by applying tensile strain to the FBG, the device is capable of detecting microstrain changes in the range of 0-200 με with a standard error of 4 με, limited by the translation stage step size. All these characteristics make it an interesting technology for filling the niche of low-cost, high-resolution wavemeters and interrogators which offer the best available trade-off between resolution, compactness, price and stability.
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