Development of radiation-hard optical links for the CMS tracker at CERN

Abstract

A radiation-hard optical link is under development for readout and control of the tracking detector in the future CMS experiment at the CERN Large Hadron Collider. We present the optical system architecture based on edge-emitting InGaAsP laser-diode transmitters operating at a wavelength of 1.3 /spl mu/m, single mode fiber ribbons, multi-way connectors and InGaAs Pin photodiode receivers. We report on radiation hardness tests of lasers, photodiodes, fibers and connectors. Increases of laser threshold and pin leakage currents with hadron fluence have been observed together with decreases in laser slope-efficiency and photodiode responsivity. Short lengths of single-mode optical fiber and multi-way connectors have been found to be little affected by radiation damage. We analyze the analog and digital performance of prototype optical links transmitting data generated at a 40M Samples/s rate. Distortion, settling time, bandwidth, noise, dynamic range and bit-error-rate results are discussed.