•Bit errors are generated differently in short distance digital parallel optical links and in long-haul single fibre (PTT) transmissions. •Where in PTT-type applications the detected light signals are sometimes so small that any noise can cause bit-errors, at CERN, parallel transmission signals remain always (exept dramatic failure) sufficiently large. Errors are mainly generated by skew problems at high transmission frequency. •However, we tried to give a basic estimation of BER under possible working conditions at CERN:

POL BER   Discussion