F. Vasey, C. Azevedo, G. Cervelli, K. Gill, R. Grabit, F. Jensen CERN, Geneva (Switzerland) !! The development phase of the optical data transfer system for the CMS tracker is nearing completion. The (50000 uni-directional analogue links used for data readout are based on edge-emitting laser transmitters and pin photodiode receivers operating at a wavelength of 1310nm. In every single-mode fibre, 256 electrical channels are time-multiplexed at a rate of 40MSamples/s. Two in-line patch-panels allow to fan-in the fibres originating from the transmitters, first to a 12-way ribbon, and then to an 8-ribbon cable carrying 96 fibres away from the detector to the counting room. All system components situated inside the detector volume (lasers, fibres and connectors) are radiation resistant and non- magnetic. The ~2000 bi-directional digital links used for control and timing distribution are based on almost identical components as the analogue readout system. Only the receiver modules placed inside the detector need to be built with radiation resistant photodiodes and discriminating amplifiers. The development options and the components used in the tracker optical data transfer system have been described previously [1]. Also, results obtained with 4-channel prototype parallel links have been presented at the last LEB workshop in Rome [2]. Integration into a complete detector readout chain and control system has since then been achieved in the laboratory. Apart from the custom designed electronics for the analogue and digital laser- drivers and photodiode-receivers, all optical link components are based on Commercial-Off-The-Shelf products (COTS). Slight deviations from the standard manufacturing process are only allowed to meet specific functionality requirements such as low back-reflection, or environmental constraints such as high magnetic field. This development strategy has the advantage of minimising development and system cost, but dictates the launch of extensive validation programmes to confirm that as wide a range of COTS as possible can be used reliably in the CMS tracker environment. Three types of validation tests are being carried out by CERN on COTS electro- optic devices supplied by industry: a) functionality tests (compliance to system specifications), b) environmental tests (resistance to radiation and magnetic field) and c) reliability tests (ageing of irradiated components). a) Functionality tests have confirmed that a variety of lasers, fibres, connectors and pin diodes can fulfil the CMS-tracker application requirements. Due to the stringent installation schedule, emphasis has first been placed on the evaluation of laser transmitters. A validation scheme has been worked out to compare different devices proposed by various manufacturers. This scheme will be presented, together with a comparative representation method of devices performance. b) Irradiation tests have been carried out extensively on lasers, pin-diodes, fibres and connectors. In order to better understand the real long-term performance of irradiated components in the CMS-tracker environment, the annealing behaviour of laser damage versus operating temperature and bias current is also being investigated. A model extrapolating laser parameter drift as a function of detector operation time and position will be presented. c) Reliability tests of irradiated lasers and pin-photodiodes have been performed during 4500 hours at 80(C. Also, irradiated connectors have been subjected to repeated mate/de-mate cycles. Results will be shown suggesting that only a minor fraction of the optical links is likely to fail during the lifetime of the experiment. Qualification tests on significant quantities of devices will take place during the pre-production phase of the project. In summary, this paper will focus on the preparation for production of a very large quantity of optical links. Market surveys have been issued for semiconductor lasers and optical connectors, and are being prepared for optical fibre cables and photodiode arrays. Samples supplied by various manufacturers are being evaluated and compared. Calls for tender will be launched in 2000. References [1] F. Vasey, V. Arbet-Engels, J. Batten, G. Cervelli, K. Gill, R. Grabit, C. Mommaert, G. Stefanini, J. Troska, "Development of radiation-hard optical links for the CMS tracker at CERN", IEEE Transactions on Nuclear Science, Vol 45, No 3, 1998, pp 331-337. [2] F. Vasey, C. Aguilar, V. Arbet-Engels, C. Azevedo, G. Cervelli, K. Gill, R. Grabit, F. Jensen, C. Mommaert, P. Moreira, "A 4-channel parallel analogue optical link for the CMS-Tracker", proceedings of the fourth workshop on electronics for LHC experiments, Rome, September 21-25, 1998, pp 344-8. !! The development phase of the optical data transfer system for the CMS tracker is nearing completion. This paper will focus on three types of validation tests carried out by CERN on Commercial-Off-The-Shelf electro-optic devices: functionality tests, environmental tests and reliability tests. The project status and the preparation for production will also be reviewed. !!