To get good fibre optic splices or terminations, especially when using the pre-polished connectors with internal splices, it is essential to cleave the fibre clearly. The term “cleaving” may be somewhat confusing. This article will give you a thorough introduction of it.
Cleaving is a process of controlled breaking of a bare fibre, which intends to create a perfectly flat endface, perpendicular to the longitudinal axis of the fibre. It begins with making a tiny scratch on the side of the fibre by using a sharp diamond, carbide or ceramic blade, before or while some defined tension or bending is applied to the fibre. Then the fibre breaks and starts at the mentioned scratch point and the scratch propagates rapidly over the full fibre cross-section, leaving a very clean surface on the obtained two fibre ends.
Note: Cleaving is not cutting just breaking in the bulk of the process. And before cleaving, a fibre coating needs to be stripped off with a coating stripper tool, or dissolved with a suitable solvent.
Cleaving is one of the important steps in the preparation for a fibre splice operation. The better results fibre cleaving has, the less splicing loss is. Otherwise, problematic cases occur. For instance, if the fibre ends are not precisely cleaved, the ends will not be mated properly. If the cleaved ends are at an angle, there will be a gap between the fibres that will cause loss in a mechanical splice or uneven fusion splicing. If there is a protrusion, or lip, on one of the fibres, the two fibres will not butt up against each other. If there are surface defects, called hackle or mist, the ends will reflect or diffuse light, causing loss.
There are two tools used for fibre optic cleaving: cleaver and pen-shaped scribe. Those two tools will be depicted in the following context to make you have a further understanding of cleaving.
A cleaver is a tool that holds the fibre under low tension, scores the surface at the proper location, then applies greater tension until the fibre breaks. As a good cleaver is automatic and produces consistent results, the user need only clamp the fibre into the cleaver and operate its controls.
A pen-shaped scribe is typically used to remove excess fibre from the end of a connector before polishing. It looks like a ballpoint pen, but has a small wedge tip made of diamond or other hard material and applied to scratch the fibre manually. It is used with the “scratch and pull” technique. First the fibre is scribed perpendicular to its length. Then the fibre is pulled to be broken at the scribe. As conducted manually, it requires experienced operators to produce good cleaves.