Abstract

High Order Fiber Bragg Gratings inscribed with fs-lasers by using the point-by-point technique are promising components for metrological purposes. In this study, we compare the radiation-induced Bragg wavelength shifts of low-diffraction-order (2) and high-diffraction-order (745) FBGs photo-written around 1550 nm at the FemtoBragg platform (CEA List) in uncoated Ge-doped and P-doped core fibers. Our interrogation setup allows us observing simultaneously 80 resonance peaks for the high order grating. We irradiated all the gratings up to 720 kGy(SiO₂) dose under X-rays. We show that low- and high-order FBGs have the same radiation response. Moreover, the RI-BWS – and by extension, the core index variation – are wavelength-independent over the studied wavelength range, despite the growth of a strong radiation-induced attenuation.

© 2023 The Author(s)