Fibre optic link technology for the CMS tracker

This note is intended to summarise the technical developments and decision elements leading to the choice of technology for the optical links in the CMS tracker. The technical aspects, relative advantages and estimated cost of the two alternatives - direct or external modulation of light - are discussed. Results of measurements of the radiation hardness of laser and modulator transmitters are presented. The choice of a system based on directly modulated laser diodes is proposed; the arguments for this choice are presented and discussed. Timescale and cost estimate of further developments required to reach production are presented.