A single-direction OTDR reading of a splice mixes real loss with any difference in backscatter between the two fibers. Shooting from both ends and averaging cancels the backscatter difference, leaving the real loss. Most acceptance specifications for spliced outside plant require bidirectional averaging, and OTDR software lines up the two traces automatically.
Spec's 0.1 dB max bidirectional average, so nobody gets paid until we've shot every fiber from the other end too.
Also heard as
- two-way averaging
Related terms
Gainer
A splice that shows an apparent gain of light on an OTDR trace, an artifact of mismatched backscatter.
Mode field diameter
The effective width of the light spot traveling in a singlemode fiber, slightly larger than the physical core.
OTDR
Optical Time Domain Reflectometer: a tester that maps a fiber's loss and events by timing light reflected back along it.
Receive cable
A reference fiber attached at the far end of a link so an OTDR can measure the loss of the last connector.
Shoot
To test a fiber with an OTDR, as in shoot the fiber or shoot it from both ends.