Response to gamma radiation of long period gratings in nanoparticle-doped optical fibers

This work demonstrates, for the first time, the inscription of long period gratings (LPGs) in nanoparticle-doped (NP-doped) optical fibers using the electric arc discharge method and their response to ionizing gamma radiation. Two types of NP-doped fibers were investigated: NPF1, featuring a silica core doped with Al surrounded by a ring of Mg-silicate NPs; and NPF2, with a germanosilicate core embedding La-silicate NPs. LPGs with various periods were inscribed and characterized, with standard Ge-doped core SMF28 fiber used as a reference. The primary objective was to evaluate the gamma radiation response of these LPGs, using a dose rate of 1.6 kGy/h up to a total dose of 32 kGy. Results showed significantly enhanced radiation-induced wavelength shifts, with NPF2 and NPF1 exhibiting maximum shifts of 26.5 nm and 18.7 nm, respectively, compared to 6.1 nm in SMF28, demonstrating an enhanced radiation sensitivity when NPs are embedded into the core. Additionally, partial recovery of the spectral features was observed after irradiation, with around 80% of the shift retained after 24 h. The superior radiation sensitivity of these NP-doped fibers, combined with the ability to fabricate stable LPGs, highlights their strong potential for optical fiber dosimetry in harsh radiation environments, including space missions. Their precise control of refractive index properties and compatibility with standard fabrication processes further strengthen their suitability for passive sensing systems.