Light-to-light readout system of the CMS electromagnetic calorimeter

For the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC) at CERN, an 80,000-crystal electromagnetic calorimeter will measure electron and photon energies with high precision over a dynamic range of roughly 16 bits. The readout electronics will be located directly behind the crystals, and must survive a total dose of up to 2/spl times/10/sup 4/ Gy along with 5/spl times/10/sup 13/ n/cm/sup 2/. A readout chain consisting of a custom wide-range acquisition circuit, commercial ADC and custom optical link for each crystal is presently under construction. An overview of the design is presented, with emphasis on the large-scale fiber communication system.