There are two main reasons for ONU weak light: equipment reasons and ODN link excessive failure. The ODN link is divided into several sections: trunk line, connection line, lead line, and home entry. Which forging section is most likely to cause the decay to exceed the standard?
Fiber optic distribution box
For weak optical ODN links, we tested the downlink optical power of PON at the trunk optical intersection and distributed optical intersection respectively, and found no obvious abnormality. During the test of the optical fiber distribution box, only about 30% of the abnormal attenuation was found, as shown in the table below, indicating that about 70% of the weak optical link problems occurred in the home segment.
Fiber optic distribution box link problem
Household cable sections usually use butterfly cables (commonly known as "leather cable"), which are less than 100 meters long, accounting for only about 1% of the entire ODN connection length. Why is there a large attenuation?
1. Fault phenomenon
What is the difference between the bending performance of commonly used G.657 and G.652 optical fibers? ", we analyzed the use of G.652 pigtails at the end of the FTTH cable at the fiber optic distribution box and the optical cat, which is the main reason for the excessive attenuation of the FTTH cable. However, about 25% of the link loss is too large, which is caused by The pigtail itself is bent.
Leather cable
The covered cable mainly uses G.657A2 optical fiber with good bending resistance system performance. Generally, when the bending radius of the covered cable does not exceed 7.5mm, the basic information of the macrobending loss can be ignored. However, the fault and the phenomenon found in the field investigation are indeed related to the bending of the leather cable.
Leather cable
When these bends loosen, the fault disappears; if not macrobend loss, what is the reason?
2. Failure cause analysis
Considering that there are forces on the leather cable in some cases, we tested the additional loss of the leather cable under bending stress and found that bending does not significantly increase the additional loss.
Leather cable test
Will it be related to the knotting of the fiber optic cable? Because from the perspective of the fault phenomenon, the leather wire and the optical cable at the fault point are often knotted. After testing, it was found that knotting does not significantly increase additional loss. Even if the cable is knotted and subjected to external forces, the additional loss will not increase significantly.
Optical Cable Troubleshooting
Through a careful study of field failure photos, it is found that in most cases, the optical cable will be twisted, so the additional loss is measured after the optical cable is twisted. The additional loss after stranding of the leather cable increases significantly. When the leather cable is twisted, the additional loss increases more obviously. Under the condition that the leather cable is twisted and knotted and then an external force is applied to test: the additional loss is as high as 3.24 decibels. The twist of the optical cable is the main cause of the additional loss. consistent with the situation at the scene.
