An optical transmission system for transmitting optical data comprises an optical transmitter, an optical receiver and a transmission medium capable of providing a visual indication of transmission status as well as the location of potential faults within the transmission medium. The optical transmitter supplies a first nonvisible light source for transmitting optical data and a second visible light source providing a visual indication of transmitter operation and possible faults. The first nonvisible light source and the second visible light source are transmitted across the transmission medium whereby they are received by the optical receiver. The optical receiver includes a filter member for removing the visible light source prior to converting the second visible light source into an electrical signal.