Precautions for Optical Fiber Test and Installation

1、 Try to avoid macro and micro music

Optical brazing, like ordinary network cables, will also have signal degradation. Network cable is mainly caused by signal decay due to distance, while for optical fiber, it is mainly caused by improper installation. For example, if the optical fiber is stretched or bent too much, it may cause the fiber core to crack and have small cracks. A direct consequence of this is that light will scatter, resulting in signal attenuation. In addition, if the bending angle of the optical fiber is too large, the incident angle of the optical fiber contacting the core cladding interface will be changed. This makes the incident angle less than the critical angle of the total reflection angle. Note that at the bend, some optical signals cannot be reflected, but refracted into the covering layer and lost directly. Reflection, refraction, these professional terms may be difficult for readers to understand. In short, when deploying optical fiber, network administrators need to avoid the following two situations as far as possible.

One is Hongqu. Macro area generally refers to the bending visible to the naked eye. Gently pull the optical fiber, you can see that the optical fiber is broken and sunk, as if it had been pressed by a heavy object. When the administrator accidentally bends the optical fiber, part of the light exceeds the critical angle, resulting in the light leaking out of the fiber core and into the covering layer. In general, once the light enters the cladding, it is difficult to return to the core again (even if it can, it is abandoned because the cost is too high). Usually, it will leak out directly through the buffer layer.

The second is micro music. Micro bending and macro bending have the same reasons, which will cause the optical signal to exceed the critical angle and leak out of the fiber core. However, the external performance is different. The existence of Hongqu can generally be judged by the naked eye. In case of micro curvature, the amplitude of occurrence is very small, which is difficult to be found by the naked eye. In other words, general bending (such as rounding the optical fiber) does not necessarily lead to micro bending. Only bending under certain conditions can lead to micro bending.

So in practice, how to avoid these two situations? A relatively simple method is not to press heavy objects on the optical fiber. Because of the long-term backlog of heavy objects, it is easy to cause optical fiber deformation, macro bending phenomenon and affect the transmission of optical fiber signal. In addition, when deploying optical fiber network, it is best to carefully observe the appearance of optical fiber. Because if macro music occurs, the appearance is obvious, which can be seen directly from the appearance (obvious backlog traces). If so, it's best to abandon this and optical fiber.

Secondly, because the micro curvature is difficult to be observed by the naked eye, the help of the instrument may be needed at this time. Connect a test instrument at both ends of the optical fiber, and then you can check the attenuation degree of the optical fiber. If it is within the range allowed by the user, there is no problem if a little macro or micro music occurs. However, if its performance has been seriously affected, the optical fiber needs to be replaced.

2、 Pay attention to whether there is an inner tube when purchasing optical fiber

The attenuation of optical fiber signal is largely related to its installation. Improper installation may lead to micro bending or macro bending. In order to avoid this situation as much as possible, many optical fiber manufacturers will add a layer of "inner tube" material to the optical fiber. The utility model relates to a material for stretching pipes, which can effectively avoid excessive bending of optical fibers.

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. It can not only improve the tensile amplitude of the optical fiber, but also ensure that the bending optical fiber is not too large. Of course, due to the addition of an inner tube, the cost will be much higher. Therefore, not every brand of optical fiber will do so. Enterprises need to pay attention to this problem when purchasing optical fiber.

3、 Pay attention to the smoothness of both ends during installation

The process of installing optical fiber is much more complex than that of installing ordinary network cable. When installing the optical fiber, both ends of the optical fiber need to be cut. In addition, the smoothness of both ends must be ensured (usually, the smoothness of the end can be ensured by polishing and other means). If the terminal is not smooth, it will lead to signal attenuation. If the network administrator has the conditions, it is better to use a microscope or built-in amplification instrument to detect the smoothness of the optical fiber end to judge its smoothness. In short, it is necessary to ensure that both ends of the optical fiber are properly polished and shaped.

After ensuring that both ends are smooth, carefully install the joints at both ends. The installation of this joint is also a technical work. Because if there is an error in the installation of the interface, such as improper splicing, or splicing two optical fibers with inconsistent dimensions together, the intensity of the optical signal will be reduced to a great extent. In general, optical fibers with different sizes are not recommended.

After the optical fiber connector is connected, certain protective measures need to be taken. This is mainly because this part is the most likely place to cause signal leakage. If the end is dusty and unclean, it will cause great attenuation when the light reaches the receiver. Make sure that the connectors and fiber ends are clean if necessary. If necessary, it is also necessary to cover the end of the optical fiber with a protective film to prevent damage. Moreover, when connecting the optical fiber to the interface of the router or switch, it needs to be cleaned again. The cleaning method is relatively simple. Generally, you only need to wipe it with alcohol free lens paper. In order to avoid dust pollution, if there is an optical fiber interface on network equipment such as switches and routers, certain protective measures need to be taken when they are not used at ordinary times. If the port is covered, prevent dust from entering. When it is reused, it needs to be cleaned again. The cleaning method is the same as that of cleaning the joint. You only need to wipe it with special paper.

4、 After installation, test and calculate the light loss

Even if the deployment method is the most appropriate or the optical fiber is the best, it is still difficult to avoid the loss of optical signal in the end, but the degree of loss is different. If the loss degree of the optical signal is within the range that the user can tolerate, then it can. On the contrary, after the maximum limit of this user has been exceeded, it is necessary to analyze the causes and take corresponding measures.

In practice, the unit of optical signal loss is measured by decibels (note that this is not a unit of sound). This unit indicates what percentage of the energy emitted by the transmitter is received by the receiver. Generally, you need to test after the first installation and confirm with the user whether you can accept this value. Note that this value needs to be recorded. This value needs to be used for reference in future maintenance. If it is found that the transmission performance of network data decreases in the process of use in the future. At this point, the administrator needs to retest it. If the test value is found to be the same as the original value, it means that there is no problem with the optical fiber, which is caused by the enterprise's own network. For example, it may be caused by the increase of data volume or the change of network architecture. It is necessary to optimize the enterprise's network. On the contrary, if the optical energy loss is found to be greater than the original, the problem that it may be an optical fiber or an optical fiber receiver transmitter must be considered. Check whether the protective layer of the optical fiber is damaged or whether there is a lot of dust on the interface, etc. It can be seen that the test of this optical fiber is very important. During the first test, the data obtained must be recorded in detail as the basis for future optical fiber maintenance and network optimization.