Performing OTDR/iOLM tests with APC connectors


Applies to

All OTDR and iOLM instruments

Information

What do I need to know when testing APC connectors with an iOLM or OTDR instrument?

A properly connected APC connector pair will generate a reflective event with typically less than 0.5 dB loss and -55 dB to -65 dB reflectance. On an OTDR trace it will be easy to identify and appear as below.

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High Reflectance

An APC connector that is damaged or soiled may generate a strong reflection, as is the case with event 3 shown below.

A screen shot of a graphAI-generated content may be incorrect.

  • If we were to zoom further, we would see that event 3 has a flat top. This means that the OTDR detector is saturated. In this case the reflectance is reported as >-23.4 dB ( stronger than -23.4 dB). 
  • We can see that this has an impact on the deadzone after event 3.
  • Using a shorter pulse (if possible) would improve the deadzone.
  • We can also see a small event ~ 20 meters beyond event 3. This is most likely an echo event created by the strong reflection at event 3 "bouncing back" from event 2.
  • If we zoom out on that trace we will see another series of what are most likely echo events. That would be events 4 and 5, and perhaps event 6. 
  • We can make this "guess" because the distances between events 1-2, 3-4, and 5-6 are all about the same (i.e. marginally longer than 2 km).

A graph of a graphAI-generated content may be incorrect.

  • In the example above, it would be best to investigate the source of the strong reflection at event 3.
  • This could explain why you are seeing events at a distance where you were not expecting connectors, splices or other components.

APC connector at the end of a fiber span

In the trace below we have an APC connector at the end of the span and the trace was taken with an 80 km distance range.

A graph of a graphAI-generated content may be incorrect.

  • An APC connector at the end of a fiber span will have a reflectance higher than -50dB, sometimes as high as -35dB. This is a physical property for a fiber to air interface of an "angled" polished connector.
  • Event 26 is the end of the fiber at 50.3 km.
  • A receive fiber that terminates with an APC connector also allows us to avoid issues associated with strong reflections at the end-of-fiber.