The OTDR's plot, with signal level in dB on the vertical axis and distance on the horizontal. A healthy fiber shows a straight downward slope; steps, spikes and an end reflection show the events. Traces are saved per fiber as the as-built record and later compared with new shots to find what changed after damage.
Pull up last year's acceptance trace and overlay it on this one, the new step at 1.8 km is our problem.
Keep every acceptance trace with fiber numbers and both directions labeled; a trace with no baseline to compare against is half as useful.
Also heard as
- signature
- OTDR trace
- shot
Related terms
OTDR
Optical Time Domain Reflectometer: a tester that maps a fiber's loss and events by timing light reflected back along it.
Event
Any point on an OTDR trace where the signal departs from the smooth fiber slope, such as a splice, connector or break.
Backscatter
The small fraction of light scattered in the fiber that travels back toward the source, which OTDRs measure.
Shoot
To test a fiber with an OTDR, as in shoot the fiber or shoot it from both ends.