Combined radiation damage, annealing, and ageing studies of InGaAsP /InP 1310 nm lasers for the CMS tracker optical links

A summary is presented of the combined effects of radiation damage, accelerated annealing and accelerated ageing in 1310 nm InGaAsP/InP multi-quantum-well lasers, the type chosen for use in the CMS Tracker optical links. The radiation damage effects are compared for a variety of radiation sources: /sup 60/Co-gamma, 0.8 MeV (average energy) neutrons, 20 MeV (average energy) neutrons and 300 MeV/c pions that represent important parts of the spectrum of particles that will be encountered in the CMS Tracker. The relative damage factors of the various sources are calculated by comparing the laser threshold current increase due to radiation damage giving approximately=0 : 0.12 : 0.53 : 1 for /sup 60/Co-gamma, approximately =0.8 MeV neutrons, approximately=20 MeV neutrons with respect to 300 MeV/c pions. The effects of bias current and temperature on the annealing were measured and, in all cases, the annealing is proportional to log(annealing time). A bias current of 60 mA increases the annealing, in terms of the time taken to anneal a given amount, by a factor of 10 relative to 0 mA. The annealing rate is also accelerated by heating the irradiated lasers and recovery occurs approximately=10 times faster at 60 degrees C than at 20 degrees C. The long-term ageing properties of irradiated lasers were also measured in an accelerated test carried out at 80 degrees C, for 2500 hours, at a bias current of 60 mA. No wearout-related degradation was observed in any of the devices. The combined results of these studies have been used to estimate the long-term damage expected for this type of laser operating inside the CMS Tracker. In the worst case of a laser operating at a distance of 22 cm from the beam-axis in the forward region of the Tracker, the maximum threshold increase will be approximately=6 mA over the first 10 years of LHC running. (20 refs).