What Is Cleaving?
To get good fiber optic splices or terminations, it is extremely important to cleave the fiber properly, especially when using the pre-polished connectors with internal splices. Cleaving is the process by which an optical fiber is “cut” or precisely broken for termination or splicing. Just like cutting glass plate, fiber is cut by scoring or scratching the surface and applying stress so the glass breaks in a smooth manner along the stress lines created by the scratch. Properly done, the fiber will cleave with a clean surface perpendicular to the length of the fiber, with no protruding glass on either end (called a lip).
Cleaving Tool – Cleaver and Scribe
A cleaver is a tool that holds the fiber under low tension, scores the surface at the proper location, then applies greater tension until the fiber breaks. Good cleavers are automatic and produce consistent results, irrespective of the operator. The user need only clamp the fiber into the cleaver and operate its controls. Some cleavers are less automated, for example requiring operators to exert force manually for breaking the fiber, making them more dependent on operator technique and therefore less predictable.
An alternative cleaving method, typically used to remove excess fiber from the end of a connector before polishing, uses a simple hand tool called a scribe. The scribe has a hard, sharp tip, generally carbide or diamond, that is used to scratch the fiber manually. Then the operator pulls the fiber to break it. Since both the scribing and breaking process are under manual control, this method is less predictable than a good cleaver, but can produce adequate results for polishing. You just need to insure that the fiber breaks totally in front of the connector ferrule so it can be polished properly.
Fiber Optic Cleaving Process
Cleaving involves introducing a nick on the glass fiber, then stressing the nick, causing it to break the fiber. If you use a scribe to introduce a nick on the fiber, you must then apply tension by pulling on the fiber to break it. However, when you use a cleaver, it not only introduces a nick on the fiber, but also applies tension with a mechanical device. The cleaving process are as follows.
1. Using the ferrule as a guide, bring the scribe in at an angle almost parallel to the ferrule surface.
2. Very gently scribe (nick) the fiber near the tip of the ferrule. Make the nick so that the size of the protruding fiber before polishing is about 100 microns.
3. Do not use excessive pressure when nicking, as it will crush the fiber and produce a shattered cleave. This results in a high-loss component because it will scatter the light transmission.
4. Break the fiber with a gentle axial tug.
Why Is Cleaving Important?
Joining two fibers requires mating two fiber ends. If the fiber ends are not precisely cleaved, the ends will not mate properly. If the cleaved ends are at an angle, there will be a gap between the fibers that will cause loss in a mechanical splice or uneven fusion splicing. If there is a protrusion, or lip, on one of the fibers, the two fibers 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.
Manufacturers of fusion splicers recognize that good cleaves are the key to low splice loss, so they equip their machines with precision cleavers. These cleavers produce cleaves that allow the machine to make virtually lossless splices every time.