The PSI-MOS-PROFIB/FO devices convert copper-based Profibus interfaces to fiber optics. The integrated optical diagnostics allow permanent monitoring of the FO paths during installation and also during operation. The floating switch contact is activated when the signal output on the fiber optic paths drops to a critical level. The PSI-MOS-PROFIB/FO T T-couplers allow the interface to be converted for two FO cables. They can be used to create linear structures and ring structures for increased system availability.