There are two main reasons for the weak light of the ONU: equipment reasons and excessive ODN link failures. The ODN link is divided into trunk, wiring, lead, and home. Which forging segment is most likely to cause excessive decay?
Optical fiber distribution box
For weak optical ODN links, we tested the downlink optical power of the PON at the trunk optical intersection and distribution optical intersection respectively, and found no obvious abnormality. During the test of the optical fiber distribution box, only about 30% abnormal attenuation was found, as shown in the following table, indicating that about 70% of the weak optical link problems occurred in the home segment.
Optical fiber distribution box link problem
The household cable section usually adopts butterfly cable (commonly known as "leather cable"), the length is less than 100 meters, and only accounts for about 1% of the entire ODN connection length. Why is there a large attenuation?
1. Fault phenomenon
What is the difference between the bending resistance of commonly used G.657 and G.652 fibers? ", we analyzed the use of G.652 pigtails at the end of the FTTH optical cable at the optical fiber distribution box and the optical cat, which is the main reason for the excessive attenuation of the FTTH optical cable. However, about 25% of the link loss is excessive, which is caused by The pigtail itself is bent.
Leather cable
The sheathed optical cable mainly uses the G.657A2 type optical fiber with good bending resistance system performance. Generally, when the bending radius of the sheathed optical cable does not exceed 7.5mm, the basic information of macrobending loss can be ignored. However, the failure and the phenomena found in the on-site investigation were indeed related to the bending of the leather cable.
Leather cable
When these bends are loosened, the fault disappears; if not macroscopic bending loss, what is the cause?
2. Failure cause analysis
Considering the stress on the leather cable in some cases, we tested the additional loss of the leather cable under bending stress and found that the bending does not significantly increase the additional loss.
Leather cable test
Could it be related to the cable knot? Because from the point of view of the fault phenomenon, the leather wire and optical cable at the fault point are often knotted. After testing, it was found that knotting does not significantly increase the additional loss. Even if the cable is knotted and subjected to external forces, the additional losses will not increase significantly.
Optical cable troubleshooting
A careful study of the field failure photos revealed that in most cases the cable is twisted, so the additional loss was measured after the cable was twisted. The additional loss of the sheathed cable after twisting increases significantly. When the leather cable is twisted, the additional loss increases more significantly. Under the condition of twisting and knotting of the leather cable and applying an external force for testing: the additional loss is as high as 3.24 decibels. Twisting of the fiber optic cable is the main cause of the additional loss. consistent with the situation on site.
3. Conclusions and Recommendations
Due to the use of G.657A2 fiber, as long as the bending radius is not less than 7.5mm, even if there is bending and knotting, the external force will not significantly increase the additional loss. However, if twisting occurs, significant additional losses will occur. If knots or even external forces are applied in the twisted state, the additional losses will increase significantly. Therefore, this should be avoided.
