VCSEL Reliability in ATLAS and development of robust arrays

Vertical Cavity Surface Emitting Lasers (VCSELs) are used for the readout and control of all ATLAS detectors at the LHC. Reliable VCSELs have been developed by using extensive Failure Analysis (FA) to eliminate or reduce the rates of random failures. Some of these FA techniques are described with illustrations from failed VCSEL channels from ATLAS operation. However VCSELs are very sensitive to several environmental factors. The reliability of the VCSELs in the different systems has been very varied. In addition to FA, controlled experiments have also been very useful in determining the cause of failures. The programmes to mitigate these failures for the two systems most affected are reviwed. A summary of VCSEL reliability and the outlook for ATLAS operation is given.