May Day eve, a optical fiber CATV network sudden emergency: two fiber node of a large number of users reflect said their TV image signal is too poor, "Snow" is very obvious. Coincided with the "five one" art show and the World Cup qualifying group stage of the Chinese national football team, if these games and literature and art programs to watch the poor quality, will certainly affect our cable network reputation.
In the emergency inspection found that the two optical nodes receiving level decreased, and the decreased significantly (7-8dB), is a concrete manifestation of the receiver output signal weakened, end users of carrier to noise ratio decreased, the screen appears a lot of noise, not normally watch. The two node for the same optical signal transmitter consists of a two optical splitter and distribution. Because two of the optical receiver and the possibility of the same fault is very small (known as the small probability events in probability theory), therefore temporarily do not consider the receiving end of the fault should be in the transmitting end and line.
Came to the room, we first check the power of the transmitter on the fault line, the transmitter's nominal optical power and measured value of the basic agreement, the problem is concentrated in the light on the road. At the end of the input sent to signal, check optical splitter output end, fading are large, the fault is determined in the splitter and its connecting pigtail on. Check the pigtail. It is found that the input side pigtail and other connecting line has a tight cross winding, winding loosen, output signal rapid recovery is often haunted the 48 hour fault excluded.
The above fault is very simple, that is, the optical fiber by external force, in the line to produce inexplicable loss of the fault. But this is often not noticed. And the faults that may be encountered on the light path are almost all of this class. Therefore, this article from the perspective of the actual maintenance of the construction and operation of the fiber should pay attention to what details to prevent the occurrence of similar failures.
Here don't discuss about the force of fiber physical properties have what kind of influence, we may wish to fiber imagine becoming a plastic hose, when by foot to step on it (applied pressure side), tube in the water will slow down or even stop the flow, and when you pack it to a certain extent, will also have a similar situation, one is fiber pigtail) under pressure, the second is subject to the fold. Obviously, they are all related to the external force. Here are the simplest explanation for these two cases.
In the first place, when the optical fiber is subjected to stress, the deformation will be produced, which will lead to the loss of the fiber.
Because the material of the optical fiber is quartz glass (SiO2), there is a certain degree of hardness, but under the pressure, its geometric form will change (for example, the cladding is not round degree increases) lead to structural defects, so that loss increases. When this kind of pressure to a certain extent, it will produce a permanent damage. In the transformation of a line, it happened because of the heat shrinkable sleeve with sand, after thermal compression fiber to make molten splicing loss in gradually increasing, and after several months in the fiber completely crushed.
Secondly, the situation of fiber bending is slightly more complicated.
Based on the electromagnetic field theory, explained that the fiber can be approximated as a cylindrical waveguide, if on the issue from the point of view of the theory of electromagnetic field to discuss will be is very complicated and abstruse, but above the about plumbing imaginary in this does not apply, not the fiber bending loss down to imagine for water in the water, because the water pipe in bending to a certain extent on the water leakage. When the optical fiber is subjected to a large bending, the bending radius is comparable with the diameter of the core, and the transmission characteristics of the optical fiber are changed. Or that it has become another type of waveguide (similar, after the compression of optical fiber and turned it into a ellipse or other shapes of the waveguide, the same is transmission characteristics was changed) no longer fit the conduction of the original message of the wavelength of light. When the wavelength of the optical fiber is suitable for the transmission of the optical fiber, a large number of the conduction mode is converted into a radiation mode, which is not continued to be transmitted, but is absorbed into the cladding layer or cladding layer. For example: Xi'an City, a continuation of the point loss has been too large, processing, technical staff will be opened to the joint box, found that optical fiber containing more confusion, some of the optical fiber bending radius smaller, re asylum after the failure to disappear.
To sum up, we should pay attention to in the construction details are as follows:
1, do not use inferior, especially have been bending the heat shrinkable sleeve, such a casing in heat shrinkage internal stress, may be imposed on the optical fiber to produce fault.
2, carrying and storing casing, pay attention to clean, don't let the sand into the casing.
3, in continuous operation, according to accommodating disc the size of stripping length, as far as possible stripping longer, the coiled fiber is calm in the closing. (in addition, should pay attention to weld after fiber asylum, it can be said that the key multi-core cable connection in the asylum)
4, continuous operation, cable stripping knife cut depth to grasp, don't make the fiber loose tube flattening force.
5, encountered in the downtown area, such as the need to lay the cable to put the optical cable, the use of the 8 - shaped disk to stay, do not allow the cable to be torque.
6, the use of stent hold cable tray laying optical cables, don't put cable tray tipped with similar from the spool on the way laying fiber optic cable, don't let the cable by the torque.
7, room as neat and, pigtail should circle around with protection, or to separate pigtail use a line, does not make between pigtail or and other connections between cross winding, try your best not to let the pigtail (even if it is temporary use) placed at the feet to step on.
8, fiber end operation (ie distribution frame), will not be tied too tight pigtail.
In addition to the above 8 details, in actual operation, there are many places that need attention, this is no longer listed one one.As long as careful, according to the standard operation, can reduce the occurrence of similar problems. The flow of the entire network, and maintain our broadcasting network reputation also has a certain significance.