I am fairly new to working with fiber optic, and hoping to get some advice from someone with more experience. I have done a lot of reading online, but there is a lot of info out there, and a lot of it either doesn't relate to what I am doing, or expects the reader to already know a lot of stuff I do not yet know.
The issue we are seeing is this - we have a fiber link between switches in two buildings. It is in two segments that are patched together. A third party company installed the fiber, but did not certify it. We have been seeing issues with communications between the buildings, and are trying to either rule out a problem with the fiber, or find and fix the issue.
We have a basic fiber tester kit from OWL, and I have watched all their training videos, and I think I am able to use the unit fairly effectively to test the loss on segments of fiber.
However, doing testing on the fiber yesterday, and we got results that I can't explain with my level of knowledge.
So, we connected the test receiver to the test transmitter with a patch cable, and zeroed the receiver. We then tested the first segment, going from the server room in one building to the server room in the other, about 1km of fiber. We showed a 1.9dB loss, which while a little higher than expected, does not appear to be high enough to be a problem.
We then tested the next segment, running from the main server room to the switch we are trying to connect to. This time, we read a 0.2dB loss, which seem right in line with what we would expect to see, as that is a much shorter piece of fiber.
Now comes the unexpected part - we then connected the whole link up, and tested end to end - so two segments of fiber, with three patch cables. One patch on each end, and the other coupling the two fiber segments. However, we now show a 15+dB loss, massively higher than adding the two segments measured loss together, even allowing some extra for the extra patch cable and couplings in the middle.
For all of this, we are using single mode fiber, testing at 1310nm, with LC connectors. We have cleaned every connector when testing and before patching. Any advice or ideas on anything that may be causing the issue, any issues with how I am testing the fiber, or anything different I should be doing to locate the problem would be very helpful!
