A good cleaver helps cut out costly mistakes

To get good fiber optic splices or terminations, especially when using the pre-polished connectors with internal splices, it is extremely important to cleave the fiber properly. The term “cleave” is somewhat confusing, as is the terminology for the tool that does the job, so let’s define our terms and look at how the process is done properly.

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).

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.

Why is proper cleaving so 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, which cost about $1,500, produce cleaves that allow the machine to make virtually lossless splices every time.

Manufacturers who sell mechanical splices or connectors that are pre-polished and use mechanical splices internally for field termination provide cleavers in their termination kits that are much less expensive (under $200) but produce much less consistent cleaves. The most popular version looks like a stapler and works about as well as one unless you practice a lot at using it.

The pre-polished splice/connectors have a reputation for high loss and poor yield (with 85 percent yield of good connectors on field terminations considered great and 30 percent not uncommon with first-time installers.) But this reputation is due primarily to problems with inexperienced installers making poor cleaves using inexpensive cleavers. There is nothing wrong with the connectors—a well-practiced installer with a good cleaver can get high yield and quick installation times with these connectors.

My advice is to buy one of the $1,500 cleavers if you plan to use a lot of mechanical splices or pre-polished splice/connectors. It will pay for itself in no time. They will produce 99.9 percent good cleaves and almost as good a yield on finished connectors. Figure it out yourself. How many discarded connectors worth $12 to $15 does it take to pay for a $1,500 cleaver? And if you look around these days, you can find good cleavers for a fraction of that price left over from the “fiber optic bubble.”

If you decide to use the inexpensive cleaver provided in most termination kits, you must learn how to use it properly. Follow directions, but also do what comes naturally to you when using the device, as they are sensitive to individual technique. Inspect the fibers you cleave to see how good they are and keep practicing until you can make consistently good cleaves. EC

HAYES is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com.