Radiation Responses of Fiber Random Gratings

Abstract

Fiber Bragg Gratings (FBGs) present numerous advantages for strain or temperature monitoring as the multiplexing ability or the high acquisition rate of interrogators. However, one FBG of the usual types cannot discriminate between temperature and strain. The new Fiber Random Gratings (FRG) present a large spectrum as opposite to the usual Bragg peak and the whole spectrum shifts varying the temperature or strain. By separating this large spectral band into smaller domains and by monitoring the response of each domain to temperature and strain, discriminating the temperature and strain contributions becomes feasible with a unique sensor. In this abstract, we study for the first time the radiation response of a type I FRG inscribed into a Ge-doped fiber with a fs-laser. Its thermal stability was checked by performing 3 cycles between $20^{\circ}\mathrm{C}$ and $60^{\circ}\mathrm{C}$ with 2 hours lasting step of $10^{\circ}\mathrm{C}$. This grating was irradiated at room temperature (RT) under X-rays, at a dose rate of 1 $\mathbf{Gy}(\mathbf{SiO}_{2})/\mathbf{s}$ up to the dose of 225 kGy. We observed a spectrum shift of approximatively 15 pm, independently of the spectral region, at the maximal dose, which represents an error of $\sim 1^{\circ}\mathrm{C}$ if the grating is used as a temperature sensor. The responses of several other RFBGs inscribed in different conditions will be added for the conference and final paper.