Information Technology Reference
In-Depth Information
Fiber-Optic Connectors
There are several types of fiber-optic connectors. We will mention three of these that
are often used in LAN wiring. The first, and one of the oldest, is the optical SMA
(SMA-905/906) connector, shown in Fig. 6.14. This connector is quite similar to the
miniature, screw-on SMA connector used for RF connections on small-diameter coax
cables. The fiber is contained in a metal or ceramic ferrule and actually comes through
to the very tip of the ferrule. The SMA connector allows very precise alignment of the
fiber, but has the disadvantage of being awkward to use. To connect the SMA, the fer-
rule must first be aligned with the mating connector, and then the outer threaded
retaining sleeve must be screwed down to hold the fiber in place. The 905-type con-
nector has a straight 3-mm ferrule. The 906-type has a step-down ferrule that allows
two ferrules to be connected by a coupler, with a plastic sleeve to align them.
SMA connectors are not designed to be easily paired together to support the
standard dual fiber interface. You must mate each fiber connector one at a time.
Also, there is no easy way to key this connector so that the transmit and receive
fibers do not get interchanged. Although this connector was once the most common
fiber-optic connector for routine LAN connections, it is not in as wide use today.
Another popular fiber-optic connector is the ST connector, shown in Fig. 6.15.
The design of this connector has a bayonet-style outer sleeve that allows the connec-
tor to be quickly inserted in its mate and secured with a quick quarter-turn. The con-
FIGURE 6.14
The optical SMA (SMA-905/906) connector. (Courtesy of Molex Fiber Optics, Inc.)
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