Radiation-hard/high-speed data transmission using optical links

The silicon trackers of the ATLAS experiment at the Large Hadron Collider (LHC) at CERN (Geneva) use optical links for data transmission. An upgrade of the trackers is planned for the Super LHC (SLHC), an upgrade of LHC with ten times higher luminosity. We investigate the radiation-hardness and bandwidth of various components for possible application in the data transmission upgrade. For the electrical connection between the front-end electronics and the optical link, we study the possible use of a micro twisted-pair cable. The bandwidth is measured to be 640 Mb/s for transmission up to 1.4 m and 320 Mb/s for transmission up to 4 m if the signal is pre-emphasized. For the optical devices, we irradiated Vertical-Cavity Surface-Emitting Laser (VCSEL) and GaAs PIN arrays from three vendors and silicon PIN arrays from one vendor. All arrays can be operated up to the SLHC dosage except for the GaAs PIN arrays, which have very low responsivities after irradiation. We have also demonstrated the feasibility of fabricating a novel optical package for housing VCSEL and PIN arrays with BeO (beryllium oxide) as the substrate for efficient removal of heat.