The majority of Fiber optic connectors are still installed in a process that uses an adhesive to attach the connector to the fiber and polishing to finish the end surface of the connector. There are three basic types of adhesives used, commonly referred to as epoxy, anaerobic and Hot Melt, which is a 3M product name. Each type has advantages and disadvantages, which we shall discuss, but all three require similar processes and skills for proper usage.
The epoxy adhesive method is the oldest and most widely used, since it is the process used in making patchcords in a factory. The epoxy is a two-part type (adhesive and hardener) that must be mixed in proper proportions to achieve the desired hardness and strength.
For field terminations, the epoxy is supplied in a two-part bag with a divider that is removed for mixing the components. After mixing, it is poured into a syringe with a flat-tipped needle to fill the connectors. Most users try to avoid this process, as it can be messy.
The syringe is inserted in the back of the connector and epoxy is squeezed out of the needle until it fills the ferrule of the connector and forms a small bead on the tip of the ferrule. This is the secret of the epoxy/polish connector.
After that bead of epoxy hardens, the connector is extremely easy to cleave and polish—easier than any other type of connector. The hardened bead supports the fiber above the end of the ferrule, so it can be scribed and broken without the possibility of breakage inside the ferrule, which ruins the connector. The bead makes polishing easier by supporting the fiber and providing an indication of how much polishing needs to be done.
Depending on the type of epoxy chosen, it can be left to harden overnight or cured in an oven in a few minutes. Oven curing is more predictable and reliable, and if one is terminating several fibers, one connector can be curing in the oven while others are being attached to the fibers or being polished. Thus the curing time in the oven becomes irrelevant to the time needed to terminate the connectors, negating the usual criticism of epoxy/ polish connectors.
Other adhesive types have been tried, but the best alternative has proven to be a class called anaerobics. These are adhesives that cure when all the air is removed, usually by isolating the adhesive in a thin film, as between the fiber and the hole in the ferrule of a connector. Industrial adhesives, such as Loctite 648, are good choices for fiber termination. But, like epoxy, there are several ways to use them.
Some methods use a syringe, filling it with the adhesive and injecting it into the connector. To get a fast cure, the fiber is dipped into a chemical that accelerates the cure of the adhesive. Then the fiber is inserted into the connector and the adhesive sets in a few seconds.
That can be too fast. If one does not immediately thread the fiber into the connector, the adhesive may set before the connector gets fully inserted, ruining the connector.
An alternative is to inject the adhesive, insert the fiber, spray the accelerator on the protruding fiber and then pull the fiber back into the connector slightly to set the adhesive in the ferrule.
Another method is to turn the adhesive bottle over to get a drop on the nozzle and wipe the fiber through it. This thin film of adhesive sets quicker and is actually stronger. It can also work without an accelerator, setting in five minutes or so, with greater strength.
Anaerobic adhesives do not leave a bead on the ferrule like epoxy, so cleaving and polishing are much more delicate operations. However, once the process is mastered, results are about as good as epoxy types.
Hot Melt connectors also use an oven, but to melt an adhesive that has already been injected in the connector at the factory. When the connector is hot and the adhesive is melted, the fiber is inserted and the assembly is allowed to cool. Then it can be cleaved and polished just like the epoxy connector.
All three of these methods produce excellent results. But like any other process that requires skills, practice is absolutely necessary. Practice should be done in your office, not on the customer site. EC
HAYES is a VDV writer and trainer and the president of The Fiber Optic Association. Find him at www.JimHayes.com.