A cleave in an optical fiber is a deliberate, controlled break, intended to create a perfectly flat endface, perpendicular to the longitudinal axis of the fiber. Since there are no crystalline planes in glass, this process is not cleavage in the crystallographic sense of the word, although the techniques used and the finished result are quite similar.
A good cleave is required for a successful splice of an optical fiber, whether by fusion or mechanical means. Also, some types of fiber-optic connectors do not employ abrasives and polishers. Instead, they use some type of cleaving technique to trim the fiber to its proper length, and produce a smooth, flat perpendicular endface.
A cleave is made by first introducing a microscopic fracture ("nick") into the fiber with a special tool, called a cleaving tool, which has a sharp blade of some hard material, such as diamond, sapphire, or tungsten carbide. If proper tension is applied to the fiber as the nick is made, or immediately afterward (this may be done by the cleaving tool in some designs, or manually in other designs), the fracture will propagate in a controlled fashion, creating the desired endface.
- Pen-shaped scribe (aka diamond-tip scribe or diamond wedge scribe) looks like a ballpoint pen, but has a small wedge tip made of diamond or other hard material. This tool is used with the "scratch and pull" technique. First the fiber is scribed perpendicular to its length. The fiber is then pulled, which breaks at the scribe. This tool requires an experienced operator to produce good cleaves.
- Mechanical cleavers clamp the fiber in the correct position before a diamond wheel or blade scribes the fiber. Then, a force is applied and the fiber gives a nice break at the scribe. Mechanical cleavers give nicer and more repeatable cleaves.
- Multifiber cleavers are used for ribbon fiber cables.
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