Fault Causes of Optical Fiber Links (1)

In the past two years, with the decrease in optical fiber costs and the wide application and upgrade of 1000Base and 10G Ethernet, optical fiber communication has gradually become an important part of LAN cabling and FTTx network construction. Due to the electromagnetic interference immunity of optical fibers, we do not need to consider the location Design of electromagnetic radiation devices such as power boxes and UPS, which greatly improves the flexibility and efficiency of integrated wiring. However, due to this, it is often subconsciously believed that the optical fiber cabling is very simple and safe, while ignoring the major network problems that may be caused by the failure of the optical fiber link.

To ensure long-distance and low-loss optical signal transmission, the entire optical fiber link must meet extremely demanding and sensitive physical conditions. Any subtle geometric deformation or slight pollution may cause a huge attenuation of the signal, or even interrupt Communication. In actual work, the main causes of cable link failure are: long optical cable, bending transition, compression or breaking of optical fiber, poor welding, mismatch of core diameter, mixed mode, mismatch of filler diameter, joint contamination, poor joint polishing and poor contact.

1. The optical cable is too long.

Due to the defects of the optical fiber and the non-uniformity of the doped components, the transmitted optical signals are always scattering and absorbing. With the improvement of manufacturing materials and manufacturing processes, today's optical fiber has reduced the attenuation of 20 dB per kilometer in 1970 to 1 dB per kilometer. At the same time, ISO 11801, ANSI/TIA/EIA 568B and other standardization organizations have also made clear provisions on the unit Distance Attenuation of Optical Fiber Links.

Even so, the attenuation of the optical fiber still exists. Therefore, when the optical fiber link is too long, the overall attenuation of the entire Link exceeds the network design threshold, resulting in a decline in the communication quality. In actual work, due to the existence of many disc lines in the optical chain, the length of the optical link is often greater than the physical distance of the actual communication node, a slight carelessness will lead to the optical link passing length. Therefore, you must specify the length of each line in the Cabling Design to prevent excessive cable length. At the same time, after the wiring is completed, the actual length of the optical link is measured by the instrument, as shown in 1 (the optifabertm of Flukenetworks can measure the length of each segment to facilitate link correction as necessary ), to ensure consistency between construction and design.

Figure 1 optifabertm optical fiber length and connection Diagram

2. Excessive Bending

Optical Cable bending loss and compression loss are essentially caused by the fact that light does not meet the conditions of full inner reflection.

Although the optical fiber can be bent, bending to a certain extent will lead to a change in the optical transmission path, so that some of the light energy can penetrate into the package layer or pass through the package layer to become the radiation mode leakage loss, resulting in bending loss. The closer the light is to the outside of the optical fiber, the higher the transmission speed. When transmitted to a certain position, the speed will exceed the speed of light, and the conduction mode becomes the radiation mode, resulting in loss. When the bending radius is over an hour, the loss caused by the bending will become very obvious. Therefore, it is generally recommended that the dynamic bending radius be no less than 20 times of the optical uniform outer diameter, and the static bending radius be no less than 15 times of the optical uniform outer diameter,

In actual use, the data in the optical fiber is transmitted along a straight line. If the optical fiber remains unchanged, the data will not be faulty. If the data is bent a little bit, it will begin to overflow; if the optical fiber is closely wound into a circle, the signal will be completely lost. Therefore, during cabling, special attention should be paid to reserving adequate angles for cabling. For example, the transmission may fail due to slight bending along the corner, corridor, and desktop.

On the other hand, bending can also be used to filter out the middle mode of the optical fiber, thus improving the stability of light attenuation Measurement. It shows the principle of attenuation of the radiation mode of optical signals in optical fiber and the process of modulation of high-order mode by scroll.