Hello, everyone!
Today, I will continue to explain OTDR and OTDR trace analysis. In this article, I begin to explain in detail each event at OTDR. This is one of the most important things to know when using OTDR.
1. Fusion splice
The connection of optical fibers is most often realized by fusion splicing. Fusion splice is the most reliable way of connecting fibers, and, it has the least attenuation and reflection. It is necessary to prepare the fibers using tools, and splicing is made by a fusion splicer. Fusion splice does not have reflectance, and IL < 0.1 dB. In the next figure, we can see the fusion splice.
Figure 1. Fusion splice
2. Connector pair
Optical connectors are used in indoor applications and wherever connection and disconnection are required. There are different types of connectors, the most commonly used are SC, LC, E2000, SC, and ST. The ferrule polishing method can be PC, UPC and APC. Which connector will be used depends on the application. Reflection and attenuation occur at the connector pair. Reflection on the PC is about -45 dB, UPC is about -55 dB and APC is up to -65 dB. IL is about 0.2-0.5 dB. The next figure shows us the connector pair on the optical trace.
Figure 2. Connector pair
3. Macro bend
Deformations occur during the optical fiber production process. These are micro bends. We can't fix them. However, bends called macro bends can occur during installation. We can measure and repair them. They are particularly well seen at high wavelengths, e.g., 1550 or 1625 nm. They are like fusion splices. There is generally no reflection, and IL depends on the wavelength. The macro bend is shown in the next figure.
Figure 3. Macro bend
4. “Gainer”
“Gainer” is the phenomenon of optical power gain, which is not possible (figure below). This phenomenon occurs because the fibers are spliced to different standards, more precisely, different core diameters. When light propagates from a small to a large core, OTDR sees this as amplification. Therefore, measurements at both ends and calculation of the mean value are required (figure below).
Figure 4. “Gainer”
Figure 5. Bidirectional analysis
I will continue on the next article >> OTDR trace analysis (4)
Thank you!
