Mechanical splice connectors are popularly used in FTTH (fiber to the home) fiber optic termination, since they are flexible, cost-effective and quick for field installation. As the FTTH network gradually becomes more widely implemented, fiber optic termination, especially indoor termination, has well become a focus of FTTH network deployment. Though current vendors can provide various types of pre-polished ferrule connectors of high quality which have low insertion loss and high performance, it is still very hard to make a perfect fiber optic termination even with advanced mechanical splicing technology. Because of inappropriate handling, fiber optic termination failures or bad fiber optic termination can occur in mechanical splice. In order to get a good termination, this article will introduce the most common factors that can lead to mechanical splice termination failures and some tips to avoid them.
Before going to the reasons for mechanical splice termination faults, let’s briefly review the steps for mechanical splicing. Firstly, the buffer coatings of fiber optic cable should be mechanically removed, by using sharp blades or calibrated stripping tools. It is important not to damage the fiber surface in any type of mechanical stripping. Then the fibers will be cleaved. After the two fiber ends are held closely and optimally aligned in a mechanical splice connector, some index gel is used between them to form a continuous optical path between fibers and reduce reflecting loss.
Mechanical splice connector is sensitive equipment. And there are many factors that can cause mechanical splice termination failures. However, most of the factors are located at the end face of optical fiber, which may include contamination, glass fragmentation, bad cleave and excessive fiber gap.
Contamination is the usually the first thing to think about when mechanical splice termination failure occurs. There are many ways that contamination can be carried into the fiber termination splices. Generally, the following incorrect operation can cause splice contamination:
1. Use a dirty cleave tool: s the fiber should be cleave before inserted in the connector, a fiber optic cleaves would be used. If a dirty cleave is used, the contamination would be attached on the end face of the fiber optic and be embedded in the connector. Thus, do remember to clean the surfaces thoroughly with alcohol wipes;
2. Wipe the fiber after cleaving;
3. Set the connector or fiber down on a dusty surface;
4. Splice in a heavy airborne dust environment;
5. Cause glass fragments from insertion broken fibers, or applying excessive force;
6. Use polluted index matching gel.
Please note that once the contamination is carried inside the mechanical splice connector, especially with the index matching gel, there would be little possibility to clean them out, which means the connector may be scrapped.
Improper operation like overexertion when inserting the fiber optic into the mechanical splice connector might break the fiber optic and produce glass fragmentation which will cause air gap and optical failure. Or if a broken fiber if inserted, there will also be optical failure. If the glass fragments are embedded in the connector, they cannot be cleaned out and the connector would be scrapped. Thus, be gentle and carefully when splicing the fiber ends.
Cleaving the fiber optic is an important step during fiber optic mechanical splicing. The quality of the cleave can decide the quality of the optical splice transmission to some degree. It is not easy to inspect the cleave quality in the field. There are several possibilities that might cause bad cleaves:
1. Use dull or chipped cleave tool blade
2. The bent tongue on the cleave tool concentrated too much bend stress on the fiber
3. Bend the fiber too much or too tight of a radius
4. Apply no tension or insufficient tension to the fiber while cleaving.
During fiber cleaving, excessive cleave angle can be produced easily and is difficult to be inspected in field. These angles are typically ranging from 1 to 3 degree. Even with precision tool, there might still be cleave angle ranging from 0.5 to 1 degree. The angle is generally produced by bent tongue, fiber bending or insufficient fiber tension.
Luckily, the cleave angles can be corrected by fine tuning with a VFL (visual fault locator). Rotating the fiber while using a VFL and terminate the connector at the right position.
Fiber gap is another factor that might cause the fiber optic termination failure. Improper operations that might cause the excessive fiber gap are listed as following:
1. Cleave the fiber without enough lengths;
2. The fiber is not fully inserted, or pulled back during termination;
3. The fiber was not held steady during termination and was pushed back into the fan-out tubing when terminating outdoor cable.
These faults can be corrected on time.
This article has introduced some factors that will lead to mechanical splice failures in fiber optic termination, and some tips are also included to ensure good splice transmission. After knowing these factors we can see that it is not enough to choose good mechanical splice connector and high quality fiber optic cleaver. Concentrating on proper operations and using right tools for mechanical splice are key to avoid bad results in mechanical splice termination.
