What Are the Different Types of Fiber-Optic Terminations?

Fiber-optic cables act as wave guides for light, primarily in high-speed data communications and to transmit pictures to video equipment. The cables are made from glass fibers usually manufactured from silica, but other materials also can be used for special purposes. Fiber-optic terminations happen at the end of a cable where it connects to a piece of equipment or to another cable. The connection of two cables is called a splice. A fiber-optic cable termination that attaches to a piece of equipment is called a connector.

Cables are manufactured in two types. Single-mode cable is generally a long-distance cable, is thinner and is more difficult to work with, but it transmits light better and is capable of higher throughput. Multi-mode cable is thicker and finds use mainly in short-distance applications such as computer networks in buildings. The fiber-optic terminations for both types of cable are similar, but most terminations for single-mode cable take place in a factory, whereas multi-mode terminations often take place in the field.

Single-mode fiber-optic terminations that take place in the field are often repairs necessitated by damage to the cable or its connectors. Splices can rejoin and repair damaged fiber-optic cables. Multi-mode cables can be spliced, but this is usually unnecessary. A multi-node cable is shorter, so a broken cable can often be easily replaced, and splicing is unnecessary. The techniques for polishing single-mode and multi-mode cable are different, and many fiber-optic cable installers lack the training for making single-mode terminations.

Termination of fiber-optic cables requires nearly perfect alignment of the cables and polished cable ends. Polished cable ends transmit more light from one cable to the next, and good alignment minimizes the amount of light that escapes from the cable end and is not received by the next cable or device. Fiber-optic terminations generally cause some loss of signal, but well-made terminations can make signal loss insignificant.

Most fiber-optic terminations to connectors made in the field will be on multi-mode cable and will use some type of adhesive termination. Adhesive terminations use epoxy to hold a cable in place inside the connector. Each fiber-optic connector manufacturer supplies its own recommended epoxy adhesive and the method of using it. Another method places the epoxy inside the connector at the factory. The connector is heated to melt the adhesive, and the fiber-optic cable is then placed inside the connector.

Crimp-type connectors were once less reliable for fiber-optic terminations, but advances in these types of connectors have made them a viable alternative to adhesive connectors. The ends of the cable still must be cut and polished, but the cable is held in place by a mechanical crimp rather than by epoxy glue. One advantage of crimp connectors is not having to wait overnight for epoxy adhesive to harden.

Splice terminations take the termination of one fiber-optic cable and connect it to another. There are two ways to splice cables together: with a weld or with a mechanical connector. The cable ends are polished, placed inside the connector and held in place by glue. Welded splices uses an electric arc to fuse the cable ends together into a single cable and don't require a connector. Regardless of the method, splices are protected inside fiber-optic splice cases.