All OTDR and iOLM instruments

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

A properly connected UPC connector pair will generate a reflective event with typically less than 0.5 dB loss and -45 dB to -55 dB reflectance. On an OTDR trace it will be easy to identify and appear as below.

High Reflectance

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

• 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).

• 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.

UPC connector at the end of a fiber span

In the trace below we have a UPC connector at the end of the span and the trace was taken with a 40 km distance range.

• A UPC connector at the end of a fiber span will have a reflectance of around -14.7 dB. This is a physical property for a fiber to air interface of a "flat" polished connector.
• Event 2 is the end of the fiber at 8.5 km.
• We can see the echo events at 17 km and 25.5 km
• In this case it would be best to set the distance range to a more appropriate value, in this example 10 km.
• Also if we use a receive fiber, that terminates with an APC connector, we can avoid issues associated with strong reflections at the end-of-fiber.

Would you like more information?

Please contact us or leave a comment if you have other questions regarding UPC connectors and OTDR testing.