Pulsed-Bremsstrahlung-Radiation Effect on Undoped- and Ge-Doped-Silica-Core Optical Fibers at Wavelength of 1.55 μm

Radiation-induced attenuation (RIA) in fibers is investigated at λ = 1.55 μm due to pulsed bremsstrahlung irradiation from an electron accelerator (mean photon energy of ~5 MeV, pulse duration of ~20 ns, doses of ~3-76 Gy, time scale of ~10
^-9
to 5 × 10
^-2
s). The fibers studied include three Ge-doped-silica-core fibers of different design and an undoped-silica-core fiber. The latter has been fabricated by an optimized technology to virtually fully suppress self-trapped holes and chlorine-associated RIA. RIA in Ge-doped fibers is found to increase with dose sublinearly with the power-law exponent in the range 0.69-0.96, although insufficient statistics (2-3 measurements for a fiber) do not allow us to state this with much confidence. The lowest RIA upon irradiation with high pulse doses (>20 Gy) is demonstrated by the undoped fiber; however, this RIA proved to be greater than that in a hollow-core photonic crystal fibers studied elsewhere. At smaller doses, RIA in the undoped fiber is estimated to amount just to a few dB/km at times 10
^-3
- 10
^-2
s. Therefore, optimized undoped fibers are argued to be the best-suited all-solid fiber type for practical applications under pulsed irradiation and combined pulsed and steady-state irradiations.