The Impact of Gamma Irradiation on Optical Fibers Identified Using Long Period Gratings

This paper compares the impact of gamma irradiation on various optical fibers, where the evolution in their optical properties could be identified using long period gratings (LPG) there induced. The LPGs were fabricated in broad spectrum of commercially available single-mode optical fibers - from standard to unconventional ones - using the electric arc discharge method. The fused silica fiber material contained such dopant as Ge, F, B/Ge and P. The gamma exposure has been performed with a dose rate of 2.6 kGy/h for 20 h (a total dose of 52 kGy). Subsequently, the recovery effect was monitored during the following 48 h. The wavelength shift and power change of the LPG attenuation bands during irradiation were investigated in real time. Moreover, to identify the impact of gamma treatment on the fiber properties, the thermal response of the gratings was studied before and after the irradiation. Depending on the fiber, significant differences have been observed in the grating responses. The highest radiation-dependent resonance wavelength shift has been found for B/Ge fiber (similar to 10 nm at maximum dose). Moreover, for these LPGs no response saturation within the applied dose levels has been observed together with very low recovery effect, what differentiate these LPGs from the other tested in this experiment. Finally, concerning the changes in optical power at the resonance wavelength, the LPG induced in P-doped fiber has shown a strong irradiation-induced attenuation reaching 18 dB with a negligible recovery effect. The findings reported in this work are crucial for optical fiber and optical fiber sensors application in environments exposed to radiation.