Irradiation studies of Gb/s optical links developed for the front-end read-out of the ATLAS liquid argon calorimeter

In the baseline read-out scheme of the ATLAS liquid argon calorimeter, approximately 1500 unidirectional Gigabit/s (Gb/s) optical links are used to transfer data from the calorimeter to receivers in data acquisition electronics situated up to 200 metres away. In the architecture of the link currently under development, VCSEL's (Vertical Cavity Surface Emitting Laser diodes) mounted on-detector are coupled to PIN-photodiodes located in receivers through graded-index multimode optical fibres. Over 10 years of ATLAS running, the components of the emitter will be exposed to high levels of neutron (1.7 x 1013 n (1 MeV Si) cm-2) and gamma (800 Gy) radiation. Their performance has been explored using neutron and gamma facilities and the results of these studies are presented in this paper. No significant levels of radiation are expected for the receiving part of the link