Hi, everybody!
I continue to explain all problems with connecting ONU. Today, I will talk about problems with ODN and how we can fix it. This is the third article about problems with ODN. In the last article, I explained – dirty optical connectors.
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 bent fibers and the problem with optical splitters.
3. Bent fibers
There are micro bending and macro bending. Micro bending occurs during the fiber production process. Macro bending occurs during the installation of optical cables. All bends introduce extra attenuation of optical fiber. We cannot influence micro bending, it is a consequence of production imperfections. We can only influence macro bending.
Each optical fiber has a certain tolerance depending on the standard. Generally, the largest fiber bends are in-home installations. Significantly smaller bends are in other parts of the network – feeder or distribution segments. Because of that, special standards have been developed for these fibers. The G.657 standard is used for drop cables. There are G.657.A1, G.657.A2, G.657.B2 and G.657.B3.
The fiber standard determines the bending radius of the fiber, as we can see in Figure 2. In the next figure, figure 3, we can see how fiber bending affects attenuation.
Problems with bent fibers are most easily observed at higher wavelengths, e.g. 1550 nm or 1650 nm. On OTDR it is a non-reflecting event like splices, at lower wavelengths we may not see it, but at higher wavelengths, it is clearly visible (non-reflecting event and increased attenuation in that point).
For finding this problem we have to use OTDR (like I said) and VFL. With VFL, we can easy to find a macro band for indoor cables - white, yellow, or orange jacket of cables. We will see a red light at that point. The solution for these problems is to correct optical cables.
Figure 1. Micro bending and macro bending losses
(http://www.uobabylon.edu.iq/eprints/publication_1_10834_324.pdf)
Figure 2. Bending radius (in mm) for standards of optical fibers G.652 and G.657
(https://www.itu.int/dms_pub/itu-t/oth/0b/04/T0B040000542C01PDFE.pdf)
Figure 3. Dependence of attenuation on bending
(https://www.itu.int/dms_pub/itu-t/oth/0b/04/T0B040000542C01PDFE.pdf)
4. Problem with optical splitters
The problem with the optical splitters (they can stop work or attenuation of the optical splitters may increase) can occur during installation or during system operation.
The problem with optical splitters during installation is easy to see and measure with a PON meter or OTDR. This problem can prevent the ONU connect to OLT.
During the work GPON system, problems with optical splitters can cause offline one or more ONUs. With NMS, such as U2000 or eSight, we can detect changes in optical power on ONUs, or we can see that ONUs have stopped working. Based on this information, technicians can find the location of the problem. OTDR and PON meter are instruments for test optical lines, too. Technicians will use these instruments to find the location of the problem.
How much offline ONUs will be, depends on whether only one or more optical splitters in the cascade are connected. If there is only one (e.g. only one optical splitter in the headend or in some building), all ONUs on that optical splitter will become offline. If they are in a cascade, and the problem is not the first optical splitter, a smaller number of ONUs will be offline or just one ONU. The problem is solved by replacing the bad optical splitter.
Thank you!
For more information, please click:
ONU failure to go online – Problems with OLT (1)
ONU failure to go online – Problems with OLT (2)
ONU failure to go online – Problems with ODN (3)
ONU failure to go online – Problems with ODN (4)
ONU failure to go online – Problems with ODN (6)
ONU failure to go online – Problems with ODN (7)
ONU failure to go online – Problems with ONU (8)
