Extraordinary Gamma Radiation Sensitivity of Long-Period Gratings Inscribed in Lutetium Aluminum Garnet-Doped Optical Fiber

In this work, we present the first experimental evidence of gamma radiation effects in a scintillating optical fiber featuring a core doped with lutetium and aluminum (LuAG), as well as cerium. These effects are related to fiber radiation-induced refractive index change (RIRIC) at infrared wavelengths, an aspect not typically examined in these fibers, and have been explored using long period grating (LPG) as a highly sensitive probe. The fiber was fabricated using a modified chemical vapor deposition (MCVD) technique combined with nanocrystal doping. During exposure to gamma irradiation at a dose rate of 1.8 kGy/h and total dose up to 4.5 kGy, the LPG resonance wavelength was monitored in real-time. Remarkably, the LPG resonance wavelength exhibited a shift of up to 50 nm, far exceeding the response observed in conventional Ge-doped fibers, while maintaining negligible radiation-induced attenuation. Post-irradiation analysis also revealed the persistence of the effects, suggesting a stable radiation-induced modification. The findings offer new insights into the design of high-sensitivity, radiation-responsive photonic components, with strong potential for applications in harsh environment sensing, nuclear monitoring, and radiation protection systems.