This actical mainly about problems with ODN and how we can fix it. This is the last article about problems with ODN. In the previous post, I explained – connected connectors of different types and connected fibers of different types.
As I said in the first article about problems with ODN, there are the following problems:
Feeder/distribution/drop fibers are broken,
Dirty optical connectors,
Bent fibers,
Problem with optical splitters,
Connected connectors of different types,
Connected fibers of different types,
Bad splices,
Incorrectly designed networks or incorrectly realized networks.
Today I will explain bad splices and incorrectly designed networks or incorrectly realized networks.
7. Bad splices
There are three types of connection optical fibers: fusion splices, mechanical splices, and optical connectors. Now, I will shortly explain fusion and mechanical splices, bad splices, and the process for fix this problem.
We choose the way of connecting fibers based on: low attenuation, low reflection, and high reliability. In addition, application and price.
The most reliable and commonly used way of connecting fibers is fusion splice. This way of connecting the optical fibers enables low attenuation, low reflection, and high reliability. It is used mainly in the feeder and distribution segments, but also in the drop part of ODN. Generally, wherever on/off fiber is not required.
For fusion splicing, we use a special machine, is fusion splicer. In short, the fibers are prepared using certain tools (e.g. cable slitter, tube cutter, fiber striper, etc.), then cleaning with alcohol or some other liquid for fibers and wipes, then the optical fibers are cut using an optical cleaver. After that, the optical fibers are connected by a fusion connector. In the end, the fusion machine checks the splice: the strength of the joint and evaluates the attenuation.
Mechanical splices are very rarely used. The reason is potentially high attenuation, high reflection, and low reliability. Index matching gel becomes obsolete over time and parameters of the mechanical splice degrades. A mechanical splice is used when we do not have a sufficient number of fusion splicers, when we rarely splice and when there is an emergency intervention. Because that, they are used a little, I will not talk about them and the problems they can cause. That will be one of the new topics.
After short explaining how to connect fibers, I will now explain the most common problems with fusion splices.
There are two main causes of bad splices. Dirty or insufficiently cleaned fibers will deviate during the process of splicing. Another problem is bad to cut fibers. The fiber must be cut at an angle of 90 degrees. This is very important to ensure a quality connection - a little attenuation and little reflection.
Sometimes fusion splicers can make a bad splice. Therefore, the electrodes and software settings should be checked.
Good splice has attenuation about 0.01 dB, max attenuation is 0.1dB. A bad splice may have a greater attenuation than the 0.1dB, values are from 1 to 5 dB. These values of attenuation can disable the connection between Huawei GPON ONT and GPON OLT such as MA5800 OLT. We can see the problem immediately after the splice is completed and repeat the splicing. After finished build the network, we must test all-optical lines by OTDR. With OTDR we can see all incorrect events on the route.
In the next two pictures, we can see the process of fusion splicing (figure 1.) and common cleave problems (figure 2.). In figure 2, there are three common cleave problems: lip, chip, and angle.
Figure 1. Process of fusion splicing
(https://imedea.uib-csic.es/~salvador/docencia/coms_optiques/addicional/ibm/ch06/06-04.html)
Figure 2. Common cleave problems
(https://www.fiberoptics4sale.com/blogs/archive-posts/95049286-fiber-optic-cleaver)
8. Incorrectly designed networks or incorrectly realized network
Sometimes an error is made during design or building and an inadequate optical splitter is installed. In this way, we don`t have the optimal number of fiber divisions. Optical power may be higher or more often lower than required. For example, instead of splitting the fiber 32 times, it is split 16 or 64 times.
We can locate this problem with OTDR or using a PON meter. Incorrect optical power can disable connections between ONUs and OLT. The problem will be fixed when we change the inadequate optical splitter.
