Smart Solutions for Single-mode Optical Fiber Connection

- Jul 25, 2019-

Single-mode fiber is called Single Mode Fiber in English. The center glass core is very thin, which can realize long-distance and high-quality signal transmission. So how to connect single mode optical fibers?

There are many methods of optical fiber connection, among which arc welding is the most widely used and the best one. This method makes use of the melting property of optical fibers at high temperature and the principle of high temperature arc generated by high voltage tip discharge to make optical fibers weld. At present, image processing technology is widely used in welding machines on the market, which can automatically set the position of the end face. Moreover, by switching the picture of the picture tube, the centring and welding of optical fibers can be observed from both vertical and horizontal aspects. The connection loss can also be estimated and displayed according to the deviation and inclination of the mandrel.

Single-mode optical fiber splicing generally has the following steps:

1. Pre-sheathed shrinkable sleeve with steel wire to reinforce the connecting part of optical cable;

2. Remove the coating layer, clamp the optical fiber vertically with the clasp, and quickly remove the 20-30 mm long primary coating and secondary coating layer. Wipe the optical fiber with the cotton ball or lens paper soaked in alcohol, wipe the core clean, and avoid the appearance of cracks and scratches on the surface of the optical fiber.

3. Cut the optical fiber and make the end face. In the optical fiber connection, the most critical process is the fabrication of the optical fiber end face. The perfection of the end face of the optical fiber decides the loss of the optical fiber connection. Fiber end surface not only needs to be flat, showing a smooth mirror area, no burrs, no defects, and vertical to the axis, but also needs to keep the end surface clean to avoid dust pollution.

There are three ways to fabricate the end face: one is the scratch method. Using a mechanical cutter, the diamond cutter scratches the surface perpendicular to the optical fiber, 10 feet away from the coating layer, and flicks lightly. The optical fiber breaks naturally at the scratch position. The second is the cutting clamp method, which uses a self-made hand-held simple clamp for cutting operation. The third is the ultrasonic electric cutting method. As long as these three methods have good appliances and proper operation, the effect of fabricating end faces is very good.

4. Put the two optical fibers to be welded into the welder, and the welder will weld them automatically.

5. Testing and evaluating the jointing performance with OTDR instrument. After meeting the jointing index, the jointing part is reinforced and protected, that is, the heat-shrinkable pipe with steel wire is melted.

6. Finally, after all the cores are connected, the receptacle receives the reexamination with OTDR instrument, and the unqualified ones need to be re-admitted or re-connected until they are qualified. The connection loss index of single mode optical fibers is generally 0.08dB. In the construction, the index can be stipulated according to the actual situation, but generally not more than 0.08dB.

Fiber splicing loss is caused by imperfection of splicing point. There are many factors affecting the imperfection of splicing point, which can be summed up into two categories: external and internal factors.

Internal cause refers to the imperfection of the optical fiber itself, which can not reduce the loss by improving the splicing process. It includes core diameter mismatch, refractive index mismatch, poor concentricity of the optical fiber, mismatch of mode field diameter. Therefore, in the splicing test, the splicing loss will appear large positive and negative phenomena. It can only make the one-way value smaller and the average value tends to zero through multiple successions, but the positive and negative phenomena can not be avoided, and the positive and negative phenomena have a certain impact on the transmission loss of optical fibers. In engineering, the same batch of optical cables should be selected as far as possible when distributing optical cables, and the A and B terminals should correspond to each other as far as possible, so as to reduce the connection loss to a certain extent.

External factors refer not to the imperfection of the optical fiber itself, but to the poor connection technology. External factors have strict requirements for successors. The deviation of transverse and longitudinal position of core, the axial angle of optical fiber and the pollution of optical fiber end face are caused by the improper maintenance and operation of welder in the process of splicing.

Finally, it should be noted that the heat-shrinkable pipe should also be clean, clean and dust-free, otherwise, when hot melting, the dust docking point will be damaged and the loss will increase. When receiving the tray, try to harvest large circles to avoid the loss caused by small circles. Optical fibers should be fixed with tape in the receiving tray, so that they can not bounce up and avoid future damage.

These are the steps and some tricks of single-mode optical fiber connection. Follow the steps above, you can easily achieve the connection.

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