Regenerated Fiber Bragg Gratings in Large Mode Area Fibers for High-Temperature Sensing

Regenerated fiber Bragg gratings (RFBGs) have been created in large mode area (LMA) fibers, and their key properties for their application as high-temperature sensors were experimentally characterized. UV written Type-I seed gratings in standard single-mode fibers (SMF-28) and in low numerical aperture LMA fibers with 125 μm and 250 μm cladding diameters were regenerated, and their wavelength drift characteristics at high temperatures, their temperature sensitivities, and their mechanical strengths were tested and compared with each other. We found that low dopant concentrations in the fiber cores led to lower wavelength drift rates during and after regeneration. A temperature calibration from room temperature to 800
$^\circ$
C showed that LMA fibers have generally similar but slightly lower temperature sensitivities than SMF-28 fibers. The tensile strength tests showed that LMA fibers with 250 μm cladding diameter have similar tensile fracture stresses as SMF-28 fibers but four times larger tensile force tolerances because of their twofold fiber diameter. Our research shows that using LMA fibers for RFBGs offers significant advantages for high-temperature sensing than their counterparts in standard fibers, which are also applicable to other silica fiber-based high-temperature sensors.