Hello,
Today I would like to share with you the issues that should be paid attention to in the erection, fusion splicing and testing of optical fibers.
With the rapid development of modern communication technology and the continuous increase of communication capacity, the requirements for the maintenance quality of optical cables are getting higher and higher. Optical cable line maintenance personnel should continuously improve their own business and technical level and improve the quality of optical cable line maintenance. The following describes the issues that should be paid attention to in the erection, fusion splicing and testing of optical fibers.
1. Erection of optical cable
Optical fiber is the most ideal medium for information transmission at present. It has the characteristics of low loss, bandwidth, and strong anti-interference. Therefore, it is widely used in communication, television, and data transmission networks. However, if it is not erected in accordance with the technical specifications, it will bring unexpected troubles when connecting.
According to the structure of the optical fiber, the core is made of brittle quartz glass fiber, with filler material, steel wire reinforcement, aluminum sheath and plastic sheath. It is afraid of breaking and not pulling (of course it cannot exceed its ultimate tensile strength). Therefore, it cannot be erected in the same way as a coaxial cable in the process of erecting it in the air. It has higher requirements. The correct approach is: it is necessary to require a professional construction team to set up, and be equipped with pay-off racks, organize a certain amount of manpower, and evenly distribute intermediate and indirect forces, erect in the order of the optical fiber distribution trays, and the openings and hooks should be uniformly distributed and evenly distributed. There should be a concave drip ditch, and there should be a margin of tens of meters at the joint of each optical cable (mainly used for the ground welding operation of the splice box or there is room for the connection after the optical cable is broken). If you do not operate according to the above specifications, it is easy to twist the optical cable, resulting in broken cores or high loss points, and it will be very troublesome to rework in the future.
2. Stripping
Master the flat, stable and fast fiber stripping method. "Ping" means that the fiber must be level. The left thumb and index finger squeeze the optical fiber to make it horizontal. The exposed length is 5cm. The remaining fiber is naturally bent between the ring finger and the little finger to increase the strength and prevent slipping. "Stable" means that the stripper should be held firmly. "Quick" means that the fiber must be stripped quickly. The fiber stripper should be perpendicular to the fiber and tilted at a certain angle in the upper direction. Then use the jaws to gently clamp the fiber, then use your right hand to push it out along the fiber axis. The whole process Be natural and smooth, all in one go.
3. Cleaning of bare fiber
The bare fiber should be cleaned according to the following two steps. (1) Observe whether the coating of the stripped part of the optical fiber is completely stripped off. If there is any residue, it should be stripped again. If there is a very small amount of coating that is not easy to peel off, you can use a cotton ball dipped in a suitable amount of alcohol, while dipping, and gradually wipe off. (2) Tear the cotton into flat fan-shaped pieces, moisten it with a little alcohol (pinch it with two fingers to prevent overflow), fold it into a "V" shape, clamp the stripped optical fiber, and wipe it along the axis of the optical fiber. Strive for success once, a piece of cotton should be replaced in time after 2 to 3 times, and different parts and layers of cotton should be used each time, which can increase the utilization rate of cotton and prevent the two pollution of fiber probe.
4. Cutting of bare fiber
Cutting is the most critical part in the preparation of optical fiber end faces. A precise and excellent cutter is the foundation, and strict and scientific operating specifications are the guarantee.
First, clean the cutter and adjust the position of the cutter. The position of the cutter should be stable. When cutting, the action should be natural and stable. Don't be heavy or hasty. Avoid fiber breaks, bevels, burrs, cracks and other bad end faces. In addition, it is necessary to allocate and use your right hand fingers reasonably to make them correspond and coordinate with the specific parts of the cutter, so as to improve the cutting speed and quality.
5. Fiber splicing
Optical fiber fusion splicing is the central link of the splicing work, so scientific operation in the splicing process is very necessary.
Fiber splicing is a very careful and serious work, and records must be made, including the number of cores, colors, order, splicing loss, etc., and the drawing of the reel. We also pay attention to welding, not just touch the two cores. The first is to choose the fusion splicer model. When the 1550nm fiber is fusion spliced, the fusion splicer should be a higher grade, and the splicing loss should be lower. Generally, it is controlled below 0.04dB. If it exceeds this value, it must be spliced again. The second is the thermoplastic pipe. The steel wire of the good quality thermoplastic pipe is not easy to fall out, and the hand feels full of elasticity. The steel wire of the low quality thermoplastic pipe is thin and hard, and looks like a wire rod after heating. Some fiber cores are still broken here after being heated and cooled after being melted. It was not known at the time. Only when the engineering welding was completed, the core was found to be broken, and the breaking point was in the thermoplastic tube. Our analysis believes that it may be caused by the unsynchronized expansion coefficient of the thermoplastic tube and the tension of the optical fiber; it may also be caused by force or vibration when the thermoplastic tube is clamped with tweezers when it is not cooled. Furthermore, the fixing method of the steel wire in the center of the optical cable cannot be ignored. The correct way is that when the steel wire passes through the fixing bolt, the underside of the steel wire must be a filling bundle tube, not a core bundle tube. If the steel wire is pressed on the core bundle tube and subjected to stress and deformation, it will cause excessive loss. Pay special attention to the 1550nm fiber. In addition, the optical fiber should be kept long (approximately 70 cm is appropriate) during splicing, so that there is room for rework in the future, and the splicing operation is also convenient. Furthermore, the bending radius of the optical fiber in the splice box cannot be too small. Too small radian will easily cause excessive refraction loss and cause dispersion.
Before fusion splicing, key parameters such as the optimal pre-melting main fusion current and time and the amount of fiber input should be set according to the material and type of the optical fiber. During the welding process, the "V" groove, electrode, objective lens, welding chamber, etc. of the welding machine should be cleaned in time, and the welding should be observed at any time for bubbles, too thin, too thick, false melting, separation, etc., and pay attention to the OTDR tracking monitoring results. Analyze the causes of the above-mentioned undesirable phenomena in time, and take corresponding improvement measures. If false fusion occurs repeatedly, check whether the materials and models of the two optical fibers to be fused are matched, whether the cutter and the fusion splicer are contaminated by dust, and check the oxidation status of the electrodes. If there is no problem, the fusion current should be appropriately increased.
Note: Beware of end-face contamination
The heat-shrinkable sleeve should be inserted before peeling, and it is strictly forbidden to pass it after the end surface is prepared. The cleaning, cutting and welding time of the bare fiber should be closely connected, and the interval should not be too long, especially the prepared end face should not be placed in the air. When moving, handle it gently to prevent rubbing against other objects. During splicing, the "V" groove, pressing plate, and blade of the cutter should be cleaned according to the environment to prevent contamination of the end face.
6. Coiling fiber
Coiling is a technique and an art. The scientific coiling method can make the optical fiber layout reasonable, the additional loss is small, and it can withstand the test of time and harsh environment, and can avoid the phenomenon of fiber breakage caused by extrusion.
The fiber is coiled in units along the loose tube or the branching direction of the optical cable. The former is suitable for all splicing projects; the latter is only suitable for the end of the main optical cable, and it has one input and multiple output. The branches are mostly small logarithmic optical cables. After fusion splicing and heat shrinking one or several optical fibers in loose tubes, or optical fibers in a branching direction optical fiber, the fiber is coiled once. It avoids the confusion of the optical fiber between the loose tube of the optical fiber or between the different branch optical cables, makes the layout reasonable, easy to reel, easy to disassemble, and more convenient for future maintenance. The fiber is coiled based on the unit for placing the heat shrinkable tube in the reserved tray, and the fiber is coiled according to the number of heat shrinkable tubes that can be placed in a small storage area in the reserved tray in the splice box. For example, the GLE-type barrel-type joint box has a plate with 6 cores in actual operation, which is extremely convenient. It avoids the unevenness of the same bundle of optical fibers due to different placement positions, difficulty in coiling and fixing, and even sharp bends and small loops. In special cases, such as optical splitter, upper/lower pigtails, pigtails and other special devices in the splicing, the ordinary optical fibers must be spliced, heat-shrinked, and coiled first, and then deal with the above situations in order. It is safe and often separate. Disc operation to prevent additional loss caused by squeezing.
Coiling method:
(1) First the middle and then the two sides, that is, put the heat-shrinked sleeves one by one in the fixed groove, and then process the remaining fibers on both sides. This will help protect the optical fiber joints and avoid possible damage caused by the coiling of the fiber. This method is often used when the optical fiber reserve has a small space and the optical fiber is difficult to coil and fix.
(2) Start the fiber winding from one end, that is, start from the fiber on one side, fix the heat shrinkable tube, and then process the remaining fiber on the other side. The location of the copper tube can be flexibly selected according to the length of the remaining fiber on one side, which is convenient and fast, and can avoid sharp bends and small circles.
(3) Treatment of special circumstances. If individual optical fibers are too long or too short, they can be coiled separately at the end; when there are special optical components, they can be treated on a separate disk. If they are co-disked with ordinary optical fibers, they can be coiled separately. Put it lightly on the ordinary optical fiber, add a buffer pad between the two to prevent the fiber from being squeezed, and the pigtail of the special optical device should not be too long.
(4) According to the actual situation, a variety of graphic disc fibers are used. According to the length of the surplus fiber and the size of the reserved disk space, take advantage of the natural coiling, do not pull it hard, and use a variety of graphic disk fibers such as circles and ellipses (note R³4cm) to maximize the use of the reserved disk space and effectively reduce The additional loss caused by the coiled fiber.
7. Optical fiber testing
After the fiber is erected and spliced, it is the test work. Nowadays, a large number of test instruments are used, and OTDR time domain meters are used. It is mainly used to test the length of the optical fiber, the attenuation value, and determine the fault location of the breakpoint and the high loss point. In order to test accurately, the pulse range of the time domain meter should be selected appropriately and set according to the index of refractive index n given by the manufacturer. When judging the fault point, if the distance length is not known in advance, put it in the automatic position first, find the rough position, and then put it in the manual position, put the pulse width range in a small position (corresponding to the distance range), and the blind zone will be reduced. Until it coincides with the coordinate line. The smaller the pulse width, the more accurate it is. Of course, when the pulse setting is too small, noise appears on the curve display, which should be just right. Then there is the addition of a fiber probe, the purpose is to prevent blind spots in the vicinity that are not easy to detect. When judging the breakpoint, if the breakpoint is not at the splice box, open the nearby splice box, connect the time domain hand, bare fiber tray, and test the exact position. When judging the high-loss point and handling it, if you find a high-loss point in the middle, but not in the connection box, use the same method as above to find the fault point according to the test distance. If it is a twist and discount, you need to manually correct it in the opposite direction. . In addition, during the optical fiber erection process, the excess optical fiber should be placed on the cup instead of being cut off. It is convenient to find the fault point accurately according to the data length of the equipped disk.
Note: the guarantee of the quality of the optical cable connection
Strengthening the monitoring of OTDR is of great significance to ensure the quality of optical fiber splicing, reduce the additional loss caused by the coil fiber and the damage that the box may cause to the optical fiber. In the entire splicing work, the four OTDR monitoring procedures must be strictly implemented: (1) Real-time tracking and monitoring of each core fiber during the splicing process to check the quality of each splice point; (2) After each fiber reel, the Perform routine inspection of the optical fiber to determine the additional loss caused by the optical fiber; (3) Before sealing the splicing box, perform a unified test on all optical fibers to find out whether there is any missing test and whether the optical fiber and connectors are squeezed between the optical fiber reserved disks. (4) After sealing the box, perform final inspection on all optical fibers to check whether the sealing box damages the optical fibers.
8. Conclusion
Optical cable continuity is a meticulous work, especially in the end-face preparation, welding, coiling and other links, requiring careful observation, careful consideration, and operating specifications. In short, in the work, we must cultivate a rigorous and meticulous work style, diligent in summing up and thinking, in order to improve practical operation skills, reduce splicing loss, and comprehensively improve the quality of optical cable splicing.
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