The reduction in power, in dB, caused by inserting something into an optical path, whether a single connector pair, a splitter or an entire installed link. For cable plant it is measured with a light source and power meter after setting a reference, and the result is compared with the calculated loss budget. Insertion loss is the number that decides whether a link passes acceptance testing.
Insertion loss on the 2 km link came in at 1.9 dB, budget was 2.4, so it passes with room to spare.
Also heard as
- IL
Do not mix it up with
- Return loss: Return loss describes light reflected back toward the source, not light lost along the path.
Related terms
OLTS
Optical Loss Test Set: a light source and power meter used together to measure end-to-end link loss.
Loss budget
The calculated total loss a fiber link should have, built from fiber length, connectors and splices.
Attenuation
The gradual loss of optical power as light travels along a fiber, expressed in decibels.
One-jumper reference
A loss-test reference set with a single launch jumper between source and meter, so both link end connectors are counted.
Connector
A removable termination that aligns the end of one fiber with another so light passes between them.