Single mode fiber, which is called single mode fiber in English. Its center glass core is very thin, which can realize long-distance, high-quality signal transmission. So how to connect single-mode fiber?
There are many methods of optical fiber connection, among which arc welding is the most widely used and the most superior one. This method makes use of the melting property of the optical fiber at high temperature and the high temperature arc principle produced by the high-pressure tip discharge, so that the optical fiber can be fused. At present, the image processing technology is widely used in the welding machine on the market, which can automatically set the position of the end face. Moreover, by switching the picture of picture tube, the centering and welding of the optical fiber can be observed from the vertical and horizontal aspects. The splicing loss can also be estimated and displayed according to the deviation and inclination of the mandrel.
Single mode fiber splicing generally has the following steps:
1. A heat shrinkable sleeve with steel wire is sheathed in advance to reinforce the connecting part of the optical cable;
2. Remove the coating layer, clamp the optical fiber vertically with the covered pliers, peel off the primary coating and secondary coating layer with the length of 20mm-30mm quickly, wipe the optical fiber with cotton ball or lens paper soaked in alcohol, wipe the core clean, and avoid cracks and scratches on the surface of the optical fiber.
3. Cut the optical fiber and make the end face. In optical fiber splicing, the most critical process is the fabrication of optical fiber end face. Whether the fiber end face is perfect or not determines the loss of fiber connection. The end face of optical fiber not only needs to be flat, showing a smooth and flat mirror area, free of burrs and defects, and perpendicular to the axis, but also needs to keep the end face clean to avoid dust pollution.
There are three methods to make the end face: one is the scoring method. Use a mechanical cutting knife, use a diamond knife to mark on the surface in the direction perpendicular to the optical fiber, 10 mm away from the coating layer, gently bump, and the optical fiber will break naturally at this scoring position. The second is the cutting pliers method, which uses a self-made hand-held simple pliers for cutting operation. Third, ultrasonic electric cutting method. As long as the apparatus is excellent and the operation is proper, the results of the three methods are very good.
4. Put the two optical fibers to be connected into the fusion machine, and the fusion machine will automatically weld them.
5. The OTDR instrument is used to test and evaluate the connection performance. After meeting the connection index, the reinforcement protection of the connection part, i.e. the heat shrinkable pipe with steel wire, is carried out.
6. Finally, after all fiber cores are connected, they shall be put into the receiving disk and retested with OTDR instrument. Unqualified fiber cores shall be received or reconnected until they are qualified. The splicing loss index of single-mode fiber is generally 0.08db. In the construction, indicators can be specified according to the actual situation, but they are generally not more than 0.08db.
The fiber splicing loss is caused by the imperfection of the splicing point. There are many factors that affect the imperfection of the splicing point, which can be summed up into two categories: external and internal factors.
The internal cause refers to the imperfection of the fiber itself, which can not be reduced by improving the splicing process. It includes core diameter mismatch, refractive index distribution mismatch, poor concentricity of the fiber, and mode field diameter mismatch. Therefore, in the splicing test, the splicing loss value will appear large positive and large negative phenomenon. Through multiple connections, the unidirectional value can only be smaller and the average value tends to zero, but the positive and negative phenomena can not be avoided. The positive and negative phenomena have a certain impact on the transmission loss of optical fiber. In the project, the same batch of optical cables shall be selected as far as possible during the distribution of optical cables, and the A and B ends shall correspond one by one as far as possible, which can reduce the connection loss to a certain extent.
External factors refer to the imperfection of non fiber itself, but the poor connection process. External factors have strict requirements on the connecting personnel. The deviation of transverse, longitudinal and axial angle of optical fiber and the pollution of optical fiber end face are caused by the untimely maintenance and improper operation of welding machine.
Finally, it should be noted that the heat shrinkable pipe should also be clean and dust-free, otherwise, the dust will damage the connection point and increase the loss during the hot melting. When receiving to the receiving tray, try to harvest in large circle to avoid the increase of loss caused by small circle. The optical fiber shall be fixed with tape in the receiving tray, without the tendency of loading, so as to avoid future damage.