Outstanding sensitivity to ionizing radiation of custom optical fibers evaluated in real-time by Long Period Gratings

In this work, we report on the gamma radiation sensitivity of different optical fibers, including a custom-designed scintillating fiber and commercially available models with different core compositions (Ge-doped, P-doped, and pure-silica). The sensitivity was comparatively investigated by monitoring the shift in the resonant wavelength of long period gratings (LPGs) inscribed in these fibers, which were exposed to a 1.8 kGy/h gamma dose rate until reaching a maximum absorbed dose of 36 kGy. The LPG period was selected to have the coupling with a high order cladding mode near 1550 nm. Additionally, post irradiation permanent effects were observed after the following two days. Real-time measurements highlighted a significant dependence of the response on the fiber composition, with the scintillating optical fiber demonstrating one order of magnitude higher sensitivity than other fibers. By tailoring the fiber composition and grating parameters, this study aims to develop fiber-based sensors capable of precise and reliable measurements in diverse radiation-rich settings, including nuclear reactors, space exploration, and particle accelerators.