How to Read and Interpret OTDR Events Test Report

An Optical Time Domain Reflector Meter (OTDR) is a high precision testing instruments used to locate events or faults in a fiber link. The OTDR combines a laser source and a detector to provide an inside view of the fiber link. The laser source sends a signal into the fiber where the detector receives the light reflected from the different elements of the link. This produces a trace on a graph made in accordance with the signal received, and a post-analysis event table that contains complete information on each network component is then generated. Then How to Read and Interpret OTDR Events Test Report, it is very important for every technician.

1. Non-reflective events

Here we see there is no reflection, just a loss for fiber optic splicing point and fiber bending. Fiber optic fusion splices are the best method for a virtually lossless connection but a high quality fusion splice is required for this.

2. Reflective Events

Fiber optic connectors, mechanical fixing connectors and fiber optic break are reflective events with a significant amount of Fresnel Reflection with a loss. Here we can see they all can cause optical power reflection and attenuation. They have similar display results on OTDR trace.

3. Fiber End

Here we can see a very large reflective event with the tail dropping off the bottom of the trace. Caution: This may not be the end of the link, it could we where the fiber is broken. That is why you MUST OTDR a link in both directions. If you OTDR in one direction at it reports 75 m and the other direction reports 62 m then you know there is a break in the cable.

4. Miss-Matched Fibers (Gainer)

This is often referred to as a gainer. Of course this is not a real gainer since all the components here are passive. IT just appears that way. In this example a 50 m fiber is connected to a 62.5 m fiber. The step up is caused by there being a higher level of scattered signal coming from the larger core fiber.

5. Ghosts

These are not real events, they are Ghosts. It is easy to anticipate where ghosts will appear on the trace and they can therefore be ignored. Also, the ghost will have no associated step down on the trace level since there is no loss at that point. This enables it to be identified as a ghost. With the OptiFiber, most Ghosts will be seen after the End Of Link.