Radiation damage studies of optoelectronic components for the CMS tracker optical links

Optical links are being developed to transfer analogue tracking data and digital timing and control signals in the future Compact Muon Solenoid (CMS) experiment at CERN. The radiation environment inside the CMS tracker will be extreme, with hadron fluences up to /spl sim/10/sup 14//cm/sup 2/ and ionising doses of /spl sim/100 kGy over the experimental lifetime. Prototype link elements, consisting of commercially available 1310 nm multi-quantum-well InGaAsP lasers and InGaAs p-i-n photodiodes, have been irradiated in a fully packaged form with /spl sim/6 MeV neutrons to 10/sup 15/ n/cm/sup 2/, 24 GeV protons to 4/spl times/10/sup 14/ p/cm/sup 2/ and /sup 60/Co-gammas to 100 kGy. Three types of single-mode optical fiber, two pure-silica core and one Ge-doped core, were irradiated in several stages with /sup 60/Co-gammas to a total dose of /spl sim/90 kGy. Neutron and proton damage induced large increases in laser threshold and significant decreases in light output efficiency. P-i-n leakage current increased by up to 6-7 orders of magnitude for neutron and proton damage. P-i-n response was relatively unaffected until /spl sim/2/spl times/10/sup 14/ n/cm/sup 2/, or /spl sim/4/spl times/10/sup 13/ p/cm, after which the photocurrent decreased rapidly. Gamma damage after 100 kGy was minor in comparison to hadron damage in both the lasers and p-i-n photodiodes. The radiation induced attenuation at 1300 nm in the optical fibers was dependent upon the fiber type, with losses of 0.08 dB/m for the pure-silica core fiber and 0.12 dB/m in the Ge-doped core fiber, after /spl sim/90 kGy. The annealing in one of the pure-silica core fibers was found to be temporary in nature.