Measurement of γ-radiation induced refractive index changes in B/Ge doped fiber using LPGs

We propose a novel approach to measure in-situ refractive index changes induced by gamma radiation in single mode fibers. The changes are derived from wavelength shifts of resonances of a CO₂ laser written long period fiber grating. Using this approach, we estimate the radiation induced refractive index increase in the core of B/Ge co-doped fiber as 2.1 × 10 ^-5 at 10 kGy and 1.85 × 10^-4 at 1.54 MGy. At doses >0.5 MGy, the index changes are considered to be governed by glass polarizability changes. Numerical simulations show that saturation of the index change can be observed at doses >15 MGy. Irradiation has a negligible effect on the resonance dip strengths and bandwidths, with the exception of the turnaround point mode.