Optical timing, trigger and control distribution for LHC detectors

Abstract

At CERN's future Large Hadron Collider, timing, trigger-accept and control signals must be distributed from a small number of sources to many thousands of front-end electronics destinations located on the ATLAS and CMS detectors. The LHC timing reference must be delivered with sub-nanosecond jitter and programmable phase. First-level trigger decisions must be broadcast from the central trigger processor to all the front-end pipeline controllers and delivered synchronously with the appropriate bunch identification, compensated for particle flight times and detector, electronics and propagation delays. In addition, broadcast control signals and individually-addressed controls and parameters such as calibration data have to be distributed. This paper describes how it is planned to broadcast all the signals over entirely passive multichannel optical fiber networks with uncontrolled path lengths. It reviews some of the technology options which are currently available and those which are likely to mature within the time frame of LHC preparation. It discusses how synchronization can be established over the system and describes how different distribution network configurations, laser transmitters and encoding methods can be used to deliver the signals using optoelectronic receivers which are becoming affordable for extensive deployment. >