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Optical Fiber Connectors

OPTICAL CONNECTORS

It used to be that you had to be an engineer to terminate optical fibers.  Now, it's almost easy enough for kids to do.

Thanks for this ease goes to optical connectors, which are used as terminating fixtures for non-fixed joints.  As such, they are designed to be plugged in and disconnected several times.

Optical connectors are available in a wide variety of styles and types.  Choosing which one to use is usually decided by the type of connector already installed in the equipment to be connected.  Nevertheless, adapters are generally available in either sleeve connectors or patch cords to allow coupling of different types of connectors.

Connectors of the same style but from different manufacturers should be compatible with one another.  For example, AT&T's ST connector can be used interchangeably with AMP's ST connector.

Some popular connectors for various applications are listed below.

Popular Connector Styles

Datacommunications Applications
(mostly multi-mode)
Telecommunications Applications
(mostly single-Mode)
ST (most commonly used) FC/PC (widely used)
SMA (decreasing in popularity) ST (single-node version)
SC (specified in many newer systems) SC (growing in popularity)
FDDI (duplex) D4 (decreasing in use)
ESCON (duplex) Biconic (decreasing in use)

INSTALLING CONNECTORS

All of the common types of connectors are fairly simple to install, although you can expect 10% loss until installers have a few days worth of experience.  After that, figure on losses of 2% to 5%, depending on the cleanliness of the area in which the connections are made.

Before the installation of connectors onto a fiber cable, a breakout kit may have to be installed.  This procedure will not be necessary on breakout cables having 2-mm buffered fibers, but will be required on 250-, 500-, and 900-micron tight-buffer cables.  The breakout kit consists of a buffer tubing (usually 2mm) over a 900-micron inner tubing.  The bare fibers are inserted into those buffer tubes to provide handling protection and strength when mounted onto connectors.

Installing a fiber connector onto a pigtail or un-buffered fiber can be done in several ways.  The three most common are epoxy glue with oven-cure, then polish; Hot Melt pre-glue, then polish; and cleave and crimp, no polish.

The epoxy-glue method is the oldest and is still widely used today.  This process involves filling the connector with a mixed two-party epoxy, then inserting the prepared and cleaned fiber into the connector.  After curing the epoxy in an oven for the specified period of time (usually 5 to 20 minutes), the fiber is scribed and cleaved nearly flush with the end of the connector.  Finally, it's polished with a succession of finer and finer lapping papers (typically ranging from 3-micron grit down to 0.3-micron grit).

With Hot Melt method (a trademark of 3M Co.), the connector comes preloaded with glue and must be placed into an oven to soften the glue.  Clean, prepared fiber is then inserted into the connector, then left to cool.  After cooling, the fiber is scribed and polished in the same process as used in the epoxy method.

Cleave and crimp connectors do not require a polish procedure since these connectors already have a polished ferrule tip.  Thus, installation simply involves inserting a properly cleaved fiber to butt against the connector's internal fiber "stub."  The fiber connector is then crimped to hold the fiber in place.

Each mounting method has advantages and disadvantages, varying from ease of installation to cost per connector to performance qualities.

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