Irradiation Studies of Multimode Fibres for use in ATLAS Front-end Links

The radiation tolerance of three multimode optical fibres has been investigatedto establish their suitability for use in the front-end data links of the ATLAS experiment. Both gamma and neutron irradiation studies are reported. A step-index fibre with a pure silica core showed an induced attenuation of $\sim$0.05~dB/mat 330~kGy(Si) and 1$\times$10$^{15}$~n(1~MeV~Si)/cm$^{2}$ and is suitablefor use with the inner detector links which operate at 40-80~Mb/s. A graded-indexfibre with a predominantly germanium doped core exhibits an induced attenuation of $\sim$0.1~dB/mat 800~Gy(Si) and 2$\times$10$^{13}$~n(1~MeV~Si)/cm$^{2}$ and is suitable for the calorimeterlinks which operate at 1.6~Gb/s. Measurements of the dose rate dependence of the induced attenuation indicate that the attenuation in ATLAS will be lower.