What are the nine reasons for the failure of optical cable links

In the past two years, with the cost reduction of optical fiber and the widespread application and upgrade of 1000 Base and 10g Ethernet, optical fiber communication has become an important part of local area network and wireless local area network cabling. So, what is the cause of the link failure?

Fiber optic cable is too long

Due to the defects of the fiber itself and the heterogeneity of the doping composition, the transmitted optical signal is scattered and absorbed. Due to the improvement of materials and manufacturing processes, the current fiber has been reduced by 20%. From DB per kilometer in 1970 to 1 DB per kilometer, at the same time standardization bodies (e.g. ISO 11801, ANSI/TIA/eia568b) clearly defined the reduction of unit distances for fiber optic links.

Nevertheless, the attenuation of the fiber itself still exists, so when the fiber link is too long, the overall attenuation of the entire link will exceed the threshold of the network design, resulting in actually, because there are many coils in the optical link, the optical chain The length of the path is usually greater than the physical distance of the actual communication node, which may result in an excessively long communication length. Therefore, the length of the line must be clearly defined in the cabling design to avoid the cable being too long. At the same time, once the cabling is completed, the actual length of the optical link is measured by the instrument, (the fiber of flukenetworks can measure each chain of the fiber optic link. length of the road) link (if required) to ensure consistency in construction and design.

overbend

The bending and compression losses of fiber optic cables are mainly due to the fact that the light does not meet the internal reflection conditions.

The fiber is somewhat bent, and although it can be bent, when the fiber is bent to a certain extent, it changes the transmission path of the light, allowing some of the light to escape. When light passes through the bend, the closer it is to the outside of the fiber, the faster it travels. It is transmitted to a given location, it travels faster than the speed of light, and the conduction mode becomes the radiation mode causing loss. When the radius of curvature passes, the resulting curvature loss becomes obvious, so it is generally recommended that the dynamic radius of curvature is not less than 20 times the outer diameter of the optical cable, and the static radius of curvature is not less than 15 times the outer diameter of the optical cable.

In practical applications, the data in the optical fiber is transmitted linearly. If the optical fiber is wound into a ring, the signal will be completely lost, so special attention should be paid to keeping a certain angle when wiring. Sufficient circuits, such as slight curved transitions along rotation angles, hallways, offices, can cause transmission failures.

In another embodiment, buckling filters higher-order modules in the fiber, which improves the stability of optical attenuation measurements. The radiation of the optical signal in the optical fiber and the modulation process of the high-level module by the disk-in-disk.

Cable is stressed or broken

The optical fiber is affected by irregular stress, such as when the fiber is subjected to pressure or the temperature change of the coated fiber, the fiber shaft can be slightly bent or even broken, so the conduction mode is converted to the radiation mode, resulting in loss of light energy, especially when the inside of the fiber optic cable occurs When breaking, if the fiber is broken due to a sudden change, the quality of the fiber signal will be greatly reduced. Then, the OTDR detector can detect the internal bending or breaking point of the fiber, and the wiring distance of the grating should be paid attention to. Local short and OTDR test instruments have high accuracy, and it is generally recommended to use test instruments with a resolution of less than 1 meter. In case of accidental death.

Poor fiber optic splicing

In fiber optic routing, two fiber segments are usually fused into one segment by fusion techniques, where skin removal is necessary because the central layer of the glass fiber has been melted. During field operation, glass fiber contamination can be caused by poor operation and unfavorable construction environment, resulting in impurities, deterioration. As shown in Figure 3, the density is too high or even bubbles during the welding process, which ultimately degrades the communication quality on the entire chain.

Therefore, whether in the hot melt process or the cold melt process, the fused fiber and the operating process are subject to strict requirements and regulations to ensure attenuation at that point. The melting point is 0.3 DB specified by TIA and ISO, for example, electromechanical welding electrodes must be cleaned before welding, glass fibers must be cleaned before welding, and the temperature and humidity of the field environment. Fiber fusion causes attenuation, and the Optifibertm can accurately determine the location and loss of each melting point.

Core diameter mismatch

Active connections are also used for fiber optic cable routing, such as flange connections. This process is flexible, simple, user-friendly, reliable and versatile. Usually, the active connection loss is about 1db, but if the end face of the fiber is not clean, the connection is not narrow and the diameter of the core is not matched, the connection loss will increase greatly. Core diameter misalignment means not only a mix of single-mode and multimode fibers, but also a mix of 62.5 and 50-strand multimode fibers.

Whether it is a mixture of patterns or a mixture of wire diameters, it is conceivable that the optical path and attenuation produced by the incident light from small diameters to large diameters and therefore, the attenuation test results of the same fiber in different directions may occur at this stage. Large changes, sometimes even leading to "decay". Negative numbers". The core diameter deviation can be easily detected using the two-terminal power test or the otr test.

It should be noted that single-mode and multi-mode fibers cannot be mixed unless the fibers have different core diameters due to transmission mode, dominant wavelength, and attenuation mechanism.

Filler diameter mismatch

Just as the diameter of the optical fiber core wire does not match, the diameter of the optical fiber core wire will also occur during the optical fiber connection process, and the inconsistency of the load will cause the optical fiber connection to fail, resulting in leakage and leakage. Attenuation of the optical signal.

Connector contamination

Fiber contamination and wet tails are the leading causes of cable communication failures, and an independent study by martintechnicalresearch found that 80% of users and 98% of suppliers have problems caused by cable ends. 70% of users and 88% of suppliers have problems due to polishing defects, a metric far higher than other causes of fiber failure.

Especially in the local network there are a large number of short hops, and a large number of switching devices, the interpolation, replacement and switching of optical fibers are very frequent. Fiber optic connectors are susceptible to contamination from dust drops, finger touches, detached plugs, etc. All these contaminants can affect the transmission of light. With fiber-optic microscopy (eg, Fiberinspector from flukenetworks), the end surfaces of dozens of nanofibers can be clearly seen, allowing the colored end surfaces to be cleaned.

Poorly polished joints

In addition to common contamination, poor street polish is one of the main failures of lighting chains, and in an ideal optical connection, the surfaces of the optical seals are flat and interconnected. Eventually, a small amount of light is reflected, and most of the light continues to pass through the end face, however, in reality, the ideal optical junction does not exist, but is more or less convex, concave, or sloping.

These defects cannot be detected with the naked eye, but when the optical signal in the bond encounters such a junction, the light generated by the irregular bonding surface is reflected more than ideally and produces an OTDR curve that indicates polishing defects. The attenuation attenuation area of ​​the terminal surface is much larger than the attenuation staining area of ​​the normal terminal surface.

Poor contact at the connector

Contact faults mainly occur at the ends of optical circuits, such as distribution boxes, optical switches, etc. Due to operator negligence and problems, the fiber optic connector is not strict enough in equipment quality or the aging of the connector can cause reflection loss and attenuation of optical signal leakage; in addition, the overflow of the installation joint can cause the optical seal to loosen, which can cause the entire optical link Drift in performance parameters.

In view of the above, although fiber optic cabling systems are completely immune to electromagnetic interference, fiber optic communication systems have many problems due to their physical characteristics (eg, excessively long fiber optic cable lengths). Fiber, bend transition of fiber, breakage, compression or welding and incompatibility of core diameter; combination of contamination modes, diameter mismatch of load, splice, polished splice, poor contact of contacts, etc. External compression and excessive bending can cause fiber deformation; impurities and air bubbles can change the density of the optical path during soldering. Linear diameter displacement, face contamination, low polish.

Optical fiber communication failures due to these physical characteristics can have different causes, performances and effects than power failures in traditional fiber optic cable communications, in addition, the accuracy of fiber optic communication makes detection difficult. Optical fiber failures are observed with the naked eye, for example, there are no failures caused by terminal surface contamination and internal rupture of the valve stem, which requires us to pay special attention to fiber routing and avoid unnecessary fiber failures due to human beings as much as possible.

At the same time, optical fiber protection instruments (such as flukenetworks simplify the photometer, the time domain of the fiber, the fiber end microscope, etc.) are used for receiving and maintenance. At the end of wiring and during routine maintenance, this can not only quickly find fiber failure problems, but also can Quickly locate and resolve problems as they occur, and ensure the security of network operations.

In order to ensure long-range and low-loss transmission of optical signals, the entire optical fiber link must meet very strict and sensitive physical conditions, and any slight geometric distortion or pollution will cause considerable signal attenuation or even communication interruption.

ZR Cable focuses on the research and development and sales of optical fiber communication products. Optical communication products include standard product optical cables, optical fiber jumpers Cables, mpo/mtp data centers, optical fiber distribution frames, etc., at ZR Cable you can buy all optical communication products in one stop.