Hello, everyone!
Today, I will continue to explain OTDR and OTDR trace analysis. In the last article, I began to explain in detail each event at OTDR. I'm continuing now.
5. Mechanical splice
The two fibers can be connected by a mechanical splice. In general, this method is rarely used because it is not reliable, and has reflection and attenuation as a connector pair. Companies that rarely splicing, or when it is necessary to quickly fix the problem with a single fiber without a fusion splicer, use this method of connecting the fibers. Over time, the performance of the index match gel degrades, and attenuation and reflection increase. In a well-made mechanical splice the reflection is about -55 dB and the IL is about 0.5 dB. Figure 6. shows us mechanical splice.
Figure 6. Mechanical splice
6. Front-end reflective event
A front-end reflective event occurs at the junction of the OTDR instrument and the reference cable. We can see it in the next figure.
Figure 7. Front-end reflective event
7. Fiber end or break
With this instrument, we can see the end of the cable, or we can find the place of the cable break. It is a reflective event.
This event is easily seen if the fiber is cut with an optical cleaver or if the fiber is finished in a patch panel. The reason is a big reflection. But if the cable is broken, the reflection is less. And it is harder to see. This is especially pronounced when the cable break is at the OTDR limit. A similar problem is with short links. That is why documentation is important.
To measure the end connector we use a reference cable at the other end of the cable (the case when we test the complete route). Reflection on the PC open to the air is about -14 dB, APC open to the air is about -45 dB, and IL is generally high.
Figure 8. Fiber end or break
8. “Ghosts”
“Ghosts” occur as a result of strong reflections (most often from a connector pair). These peaks, or ghosts, occur at a location where there is not supported to be a connection. They will be at a distance that is a multiple of the distance to a reflectance event. IL is 0 dB.
Figure 9. “Ghosts”
Continued in the next article >> OTDR trace analysis (5)
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