Irradiation studies of multimode optical fibres for use in ATLAS front-end links

The radiation tolerance of three multimode optical fibres has been investigated to establish their suitability for the 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 ∼0.05dB/m at 330kGy(Si) and 1×1015n(1MeVSi)/cm2 and is suitable for use with the inner detector links which operate at 40–80Mb/s. A graded-index fibre with a predominantly germanium-doped core exhibits an induced attenuation of ∼0.1dB/m at 800Gy(Si) and 2×1013n(1MeVSi)/cm2 and is suitable for the calorimeter links which operate at 1.6Gb/s. Measurements of the dose rate dependence of the induced attenuation indicate that the attenuation in ATLAS will be lower.