"Light into copper" is the development trend of broadband and bidirectional cable TV networks. The cable TV network transformation should further promote optical fiber to the user end to achieve the goals of high reliability, high bandwidth, high carrying capacity, manageability and operation. . In the current two-way network transformation, fiber-to-cell, fiber-to-building, and even fiber-to-the-home have become a reality. Fiber has been used in an unprecedentedly wide range. How to make better use of fiber transmission frequency bandwidth, large communication capacity, low loss, and no electromagnetic interference , The small diameter of the optical cable, light weight, abundant raw materials and other advantages are worthy of our attention. The transmission of light in the optical fiber will cause loss. This loss is mainly composed of the transmission loss of the optical fiber itself and the fusion loss at the fiber joint. Once the optical cable is ordered, the transmission loss of the optical fiber itself is basically determined, and the fusion loss at the optical fiber connector is related to the optical fiber itself and on-site construction. The steps and methods of the optical cable connection project in our county are now introduced.
1 Design and drawing of optical fiber connection drawings
(1) Selection of the number of fiber cores. Our county has newly set up optical nodes to arrange 4-core optical cables, using 1 optical fiber to transmit downstream signals, 1 to transmit upstream signals, 1 to transmit digital signals, plus 1 reserved. At the same time, when considering that several optical nodes are in the same direction, for the convenience of erecting, according to the distance of the distance end, the optical fiber used for the optical node at the farthest point is included in the optical cable that is close to the front end in sequence, for example, 3 optical nodes are in the same direction In the direction, set a 4-core fiber at each point. When setting up the optical cable, use a 12-core optical cable from the front end to the first optical node, and use an 8-core optical cable from the first optical node to the second optical node. A 4-core optical cable is used between each optical node and the third optical node, so that the multi-fiber common cable saves investment.
(2) Drawing of optical fiber cable connection drawings. After designing the number of optical fiber cores, and then start drawing optical fiber connection drawings, a complete optical cable connection routing diagram should be composed of optical link schematic diagram, optical cable fusion diagram, optical cable routing diagram, optical cable connection routing diagram, optical link loss table, etc. composition. Before the optical cable is connected, the planning and design department provides the optical cable fusion plan to the construction department.The optical cable fusion icon describes the various elements of the optical cable fusion, including the location of the optical package, the optical cable route, the number of optical cables, the number of cores, the optical cable cross-section diagram, the optical cable docking Figure etc. The optical fiber chromatogram of the loose tube in the loose tube is arranged in accordance with the color spectrum of the cable blue, orange, green, brown, gray, native, red, black, yellow, purple. There are two common optical fiber chromatograms ^^^ white and light red Ranked before the corresponding color, the cable chromatographic sorting method can form a more unified specification in the design and construction of the optical cable project, which is easy to remember and organize.
2 Optical cable connection steps
(1) The heat shrinkable sleeve should be inserted before peeling, and it is strictly forbidden to penetrate after the end surface is prepared.
(2) Preparation of end faces. The preparation of the fiber end face includes several steps of stripping, cleaning and cutting. A qualified fiber end face is a necessary condition for fusion splicing, and the quality of the end face directly affects the fusion splice quality. The stripping of the coating layer of the optical fiber should be controlled by the three-character stripping method of flat, stable and fast. "Flat. That means holding the fiber flat, squeeze the fiber with the left thumb and index finger to make it horizontal, and the exposed length is about 5 cm. The extra fiber bends naturally between the ring finger and the little finger to increase the strength and prevent slippage. "Stable. That is, the fiber stripper should be held firmly. "Fast", that is, the fiber stripping should be fast. The fiber stripping pliers should be perpendicular to the fiber, tilted at an angle in the upper direction, and then gently clamp the fiber with the jaws, and then use your right hand to force it and push it out along the fiber axis. The whole process To be natural and smooth, in one go. To clean the bare fiber, first observe whether the coating layer of the stripped part of the optical fiber is completely stripped. If there is any residue, it should be stripped again. If there is a very small amount of coating layer that is not easy to strip, use a cotton ball dipped in an appropriate amount of alcohol and gradually rub it while immersing it. except. Tear the cotton into small fan-shaped pieces with a flat surface, dip a little alcohol (preferably pinch two fingers without overflow), fold it into a "V" shape, clamp the stripped fiber, wipe it along the fiber axis, and strive for a success , A piece of cotton should be replaced in a timely manner after 2 to 3 times of use, each time using different parts and layers of the cotton, which can not only improve the cotton utilization rate, but also prevent two pollutions of fiber detection. Cleavage is the most critical part in the preparation of optical fiber end faces. Precision and excellent cutters are the basis, and strict and scientific operation specifications are guaranteed. First check the drawings and documents to understand the placement of the type of optical fiber at this connection. You should pay attention to "front-to-back, advanced, and backward", that is, holding the optical fiber, slightly ahead of the scale, it needs to be placed in the guide groove, and the rear part is lifted up slightly so that The front half of the fiber is pressed against the bottom of the guide groove, and then pulled back to the required scale to ensure that the fiber matches the "V. The guide groove is perpendicular to the blade. When cutting, the action should be natural, smooth, do not be heavy, do not rush, and avoid fiber breakage. Bevel, burrs, cracks and other bad end faces.
(3) Fiber fusion. Optical fiber fusion splicing is the central part of the splicing work, so high-performance fusion splicer and scientific operation in the fusion splicing process are necessary. Before fusion splicing, according to the material and type of optical fiber, set the best pre-melting main fusion current and time and the key parameters of optical fiber feeding. During the welding process, the welding “V†groove, electrode, objective lens, welding chamber, etc. should be cleaned in time. Observe whether there are bubbles, too thin, too thick, virtual fusion, separation and other bad phenomena in the welding, pay attention to the OTDR tracking monitoring results, timely Analyze the causes of the above-mentioned undesirable phenomena and take corresponding improvement measures. If the phenomenon of false fusion occurs many times, you should check whether the materials and models of the two spliced ​​fibers match, whether the cutter and fusion splicer are contaminated with dust, and check the electrode oxidation status. If there is no problem, the fusion current should be appropriately increased.
(4) Disk fiber. Plate fiber is a technology, but also an art. The scientific fiber coiling method can make the fiber layout reasonable, the additional loss is small, can stand the test of time and harsh environment, and can avoid the phenomenon of fiber breakage caused by extrusion. The method of coiling fiber: 1. The middle and then the two sides, that is, the heat-shrinkable sleeves are placed one by one in the fixed groove, and then the residual fibers on both sides are processed, which is beneficial to protect the fiber contacts and avoid damage caused by the coiled fiber. 2. Start the fiber coil from one end, that is, start from the fiber coil on one side, fix the heat shrinkable tube, and then process the remaining fiber on the other side. This is convenient and fast, and can avoid sharp bends and small circles. 3. For special cases, if individual fiber is too long or too short, it can be coiled separately at the end. When it has special optical device, it can be handled separately. If it is co-coiled with ordinary fiber, it should be lighter. Place it on top of ordinary optical fiber with a cushion between them to prevent fiber breakage caused by extrusion, and the pigtails of special optical devices should not be too long. 4. According to the actual situation, a variety of graphic disk fibers are used. According to the length of the remaining fiber and the size of the reserved disk space, the natural coiling takes advantage of the trend. Do not pull hard. You should use round, elliptical, CC, and various graphic disk fibers flexibly (note R) 4 cm), use the reserved disk space as much as possible and effectively reduce the additional loss caused by the disk fiber.
(5) Quality inspection of optical cable connection. Strengthening the monitoring of the OTDR is of great significance to ensure the quality of the optical fiber fusion, reduce the additional loss caused by the coiled fiber and the damage that the sealing box may cause to the optical fiber. Throughout the connection process, the OTDR 4 monitoring procedures must be strictly implemented:
1. Real-time tracking and monitoring of each core fiber during the fusion process to check the quality of each melting point; 2. After each coil fiber, routine inspection of the coil fiber to determine the additional loss caused by the coil fiber; 3. Before connecting the box, conduct a unified test on all optical fibers to find out whether there is a leak test and whether there is any squeezing of the optical fiber and the connector between the optical fiber reservation trays; 4. After the box is sealed, perform a final test on all the fibers to check whether the box is sealed Damage to the fiber. After 4 tests, detailed record of optical cable connection loss test table.
(6) Fixing of optical cable splice box and handling of residual cables. The underground splice well horizontal connection box should be on the ground first, take the box body as the reference point, circle the optical fiber cable, and then drag it into the well. Do not hang with thin wire. The vertical head connection box should pay attention to the horizontal steering of the box body, so that the incoming and outgoing optical cables are naturally free of twisting and control the bending curve of the optical cable. Specific operation methods: 1 multi-person operation forms a party coordination of the residual cable one get one pull, in principle There is only one person at the box and each remaining cable rack. It is strictly forbidden for one person to sing the double reed, and if necessary, it is equipped with a walkie-talkie to enhance communication. 2 First drag the middle and then the two sides, that is, the box body, fix it on the steel wire, and then deal with the residual cable on both sides. When the residual cable itself twists, run it along the steel wire to the opposite end in advance. When it is not necessary to deal with the residual cable, the box body should be fixed first, and then all the residual cable should be hung to the opposite end of the rod end. Beware of the damage to the connection box and the optical fiber in the secondary construction.
(7) Optical cable connection record. After the completion of the optical cable connection, make all the records in time, including the sequence, number of cores, chromatography, connection loss, etc.
3 Other issues that should be noted in fiber connection
(1) When stripping the optical cable before fusion splicing, be sure to cut the start end of the optical cable pulled when laying the optical cable to more than 2 m, because the pulling force will always have an adverse effect on this section of fiber. For parallel wire cable, due to the pulling force, the loose tube has a slow shrinkage phenomenon, which will shrink in place for at least half a year or even a year. This shrinkage phenomenon sometimes pulls the optical fiber off, so it should be pulled on the side after the cable is stripped. While holding the wire, pull the outer protective layer of the cable back to minimize the shrinkage factor.
(2) Be sure to clamp the metal reinforcing core of the optical cable and the connector box, and bend the reinforcing core. When there are many fiber optic cable bundle tubes, according to the arrangement of the fusion tray and the bundle tube, they should be reasonably separated from the reinforcing core to prevent the fiber cable bundle tube from being twisted, resulting in the fiber being tensioned or even broken.
(3) The quality of the selected shrink tube must be qualified. The metal wire in the tube should be straight and hard. The tube must not be bent or deformed. It should be matched with the slot in the joint box. When placing multiple fusion joints, the slot should be There is no pressure and there is still a gap, this is because the clamping groove is too tight, which may cause the optical fiber in the shrink tube to break. In addition, when placing the fusion joint with both hands, hold both ends with your thumb and index finger so that no force is applied to the middle (because the fusion joint is in the middle position) to prevent the fusion joint from breaking.
(4) In the case of a large number of optical fibers, the length of the fiber is often different, and it must be fixed in turn with insulating tape, otherwise the optical fiber with the excess length spliced ​​is easily ejected, and it is easily pressed by the waterproof glue of the splice box It leads to excessive loss, so try to make the length of the fiber fusion splicing the same when stripping the fiber, and at the same time check whether there is any fiber ejection outside the tray when packing.
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