A feature the OTDR flags in its event table with a distance, loss and, for reflective ones, a reflectance. Reflective events, connectors, mechanical splices and breaks, show as spikes; non-reflective events, fusion splices and bends, show as steps down. The end event marks where the fiber stops, and comparing event positions with the as-built drawings locates faults in the field.
Event at 3.42 km, 0.8 dB, non-reflective, that's right where the cable crosses the creek bridge.
Related terms
Trace
The graph an OTDR produces, plotting returned power in dB against distance along the fiber.
OTDR
Optical Time Domain Reflectometer: a tester that maps a fiber's loss and events by timing light reflected back along it.
Reflectance
The fraction of light reflected by a single event such as a connector, in dB, where more negative is better.
Macrobend
A bend in a fiber tight enough to see, which lets light escape the core and causes loss.
Event dead zone
The distance after a reflective event during which an OTDR cannot detect a second, separate event.