Precautions for optical fiber test installation

Although optical brazing can provide a lot of bandwidth, its performance will be compromised if it is not properly deployed. To this end, the author has the following suggestions for companies with optical brazing needs.

1. Try to avoid macro and micro music

Just like ordinary network cables, optical soldering may also have signal degradation. The network cable is mainly caused by the decline of the signal due to the distance, and for the optical fiber, it is mainly caused by improper installation. If the optical fiber is stretched or bent too much, it may cause the core to split and there will be small cracks. One consequence of this is that light will scatter and cause signal attenuation. In addition, if the bending angle of the optical fiber is too large, it will change the incident angle of the optical fiber contacting the core-cladding junction. This will make the incident angle smaller than the critical angle of the total reflection angle. Note that at the bend, some optical signals cannot be reflected, but are refracted into the cover layer and lost directly. Reflection, refraction, these professional terms may be difficult for readers to understand. Simply put, network administrators need to avoid the following two situations when deploying fiber.

One is Hongqu. The macro area generally refers to the curvature visible to the naked eye. Pull the fiber lightly, you can see that the fiber has a break and sink, as if it was pressed by a heavy object. When the administrator accidentally bends the optical fiber, part of the light exceeds the critical angle, causing the light to leak out of the core and enter the cover layer. In general, once light enters the cover layer, it is difficult to return to the core again (even if it can be abandoned because the cost is too high). Normally, it will leak directly through the buffer layer.

The second is micro music. Microcurve and Hongqu are more consistent in terms of cause, which will cause the optical signal to exceed the critical angle and leak out of the core. However, the external performance is different. In the case of Hongqu, it is generally possible to determine whether it exists by the naked eye. The micro-curvature, however, has a very small amplitude and is difficult to detect with the naked eye. That is to say, general bending (such as making the fiber round) does not necessarily lead to slight curvature. Only bending under certain conditions may cause microbending.

So in practical work, how to avoid these two situations? A simpler method is not to place heavy objects on the fiber. Because the backlog of heavy objects for a long time, it is easy to cause the optical fiber to deform, produce macrobends, and affect the transmission of optical fiber signals. In addition, when deploying a fiber optic network, it is best to carefully observe the appearance of the fiber. Because if the macro song occurs, the appearance is more obvious, you can see it directly from the appearance (to be obvious backlog traces). If so, it is best to discard this fiber.

Secondly, because the microbends are difficult to observe with the naked eye, you may need the help of the instrument at this time. Connect a test instrument to both ends of the fiber, and then you can check the attenuation of the fiber. If it is within the range allowed by the user, there is no problem with a little macro or micro music. But if the performance has been seriously affected, the fiber needs to be replaced.

Second, when buying optical fiber, you need to pay attention to whether there is an inner tube

The attenuation of the optical fiber signal is largely related to its installation. Improper installation may cause undesirable phenomena such as micro song or macro song. In order to avoid this as much as possible, many fiber manufacturers now add a layer of "inner tube" material to the fiber. This kind of tube stretching material can effectively avoid excessive bending of the optical fiber.

In terms of hardness, the inner tube is much harder than the optical fiber, so it is not easy to be excessively bent. Therefore, the optical fiber protected by the inner tube is usually not easy to bend. According to the laboratory test results, it can be found that the inner tube can indeed protect the optical fiber. Not only can the fiber's stretch be increased, but it can also ensure that the bent fiber is not too large. Of course, since an inner tube is added, its cost is much higher. So not every brand of fiber will do this. Enterprises need to pay attention to this problem when purchasing optical fiber.

3. When installing, pay attention to the smoothness of both ends

The installation of optical fibers is much more complicated than the installation of ordinary network cables. When installing an optical fiber, both ends of the fiber need to be cut open. Moreover, it is necessary to ensure the smoothness of both ends (usually, the smoothness of the end can be ensured by polishing and other means). If the end is not smooth, it will cause signal attenuation. If the network administrator has the conditions, it is best to use a microscope or built-in magnification instrument to detect the smoothness of the fiber end to determine its smoothness. In short, it is necessary to ensure that both ends of the fiber are properly polished and shaped.

After making sure that both ends are smooth, carefully install the connectors at both ends. The installation of this joint is also a technical task. Because if the interface is installed with errors, such as improper splicing, or splicing two optical fibers with different sizes together, the intensity of the optical signal will be greatly reduced. Generally, it is not recommended to use optical fibers with different sizes.

After the optical fiber connector is connected, certain protective measures need to be taken for it. This is mainly because this part is the most likely place to cause signal leakage. If there is dust or dirt at the end, it will cause a great attenuation of light when it reaches the receiver. If you need to make sure that the connectors and fiber ends are kept clean. If necessary, it is necessary to cover the end of the optical fiber with a protective film to prevent damage. And it needs to be cleaned again when connecting the fiber to the interface of the router or switch. The cleaning method is relatively simple, generally only need to use alcohol-free cotton-free lens paper to wipe. In order to avoid dust pollution, on network devices such as switches and routers, if there is an optical fiber interface, certain protective measures need to be taken when they are not usually used. Cover the port to prevent dust from entering. When it is used again, it needs to be cleaned again. The method of cleaning is the same as the method of cleaning the connectors, just use special paper to wipe.

Fourth, after the installation is complete, test and calculate the loss of light

Even if the deployment method is the most appropriate or the optical fiber used is the best, it is still difficult to avoid the loss of optical signals at the end, but the degree of loss is different. If the loss of this optical signal is within the range that the user can tolerate, then it is okay. On the contrary, after exceeding the user's maximum limit, you need to analyze the cause and take corresponding measures.

In actual work, the unit of optical signal loss is measured by decibels (note that this is not a unit of measuring sound). This unit indicates how much of the energy emitted by the transmitter is received by the receiver. Under normal circumstances, after the first installation is complete, you need to test and confirm with the user whether you can accept this value. Note that this value needs to be recorded. Because this value needs to be used for reference in future maintenance. In the future, it is found that the transmission performance of network data is degraded during use. At this point, the administrator needs to test it again. If the test value is found to be the same as the original, it means that there is no problem with the fiber. It is caused by the enterprise's own network. If it may be caused by the increase in data volume or the change of the network architecture, the enterprise network needs to be optimized. On the contrary, if it is found that the loss of light energy is greater than the original, then it is necessary to consider the problem that may be the optical fiber or the optical fiber receiving transmitter. Check whether the protective layer of the optical fiber is damaged or there is a lot of dust on the interface. It can be seen that the test of this fiber is very important. During the first test, the data obtained must be recorded in one hundred and fifty to serve as the basis for future fiber maintenance and network optimization.

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