By now you should know that an OTDR calculates signal loss based on the amount of reflected light, or backscatter, that it detects. Connection points along the fiber demonstrate a large reflection, which is used to determine the return loss of the connection. When there is a poor connection, light can bounce multiple times between events. Not only will light be reflected back towards the OTDR, it will also reflect in the opposite direction towards the far end, which is then reflected back again. The result of these ‘echos’ of light bouncing back and forth between events are non-existent events that show up on an OTDR trace. These ghosts are pretty spooky–you can see them on the trace, but they aren’t really there.
