Information Technology Reference
In-Depth Information
Jacket
Kevlar strands
(strength member)
Tight buffer
Primary coating
Cladding
Core
Cross-section
Side view
FIGURE 11.3
Tight-buffer fiber-optic cord construction.
Tight-Buffer Cable.
One of the two main fiber cable constructions is called tight
buffer. As you can see in Fig. 11.3, which illustrates a single-strand cable, the buffer
layer is between the fiber's primary coating and the outer strength and jacket lay-
ers. In a tight-buffer cable, the buffer is a plastic coating that separates the bare
fiber from these outer layers, and protects the fiber as the outer layers are removed.
A multifiber tight-buffer cable has two or more of the buffered fibers, which may
be additionally covered by an individual jacket and one or more spacer/strength
members.
During installation (called
termination
), the outer jacket and the fine strands
of the strength layer are removed with a sharp blade or a cable stripping tool, leav-
ing what appears to be a small-diameter flexible strand. This strand is the bare fiber
(consisting of the fiber core, cladding, and primary coating) plus the tight buffer. A
precision tool, which is basically like a wire stripper, is used to exactly cut the buffer
sleeve without nicking the bare fiber. The plastic buffer is then removed by gently
pulling the stripping tool toward the cut end of the fiber. The plastic primary coat-
ing may also be removed during this process. The fiber is then cleaned with an
appropriate solvent, such as alcohol. After some additional steps, the remaining
bare fiber is trimmed and terminated into an appropriate fiber connector.
Tight-buffer cables are often used where a small number of fibers are to be
pulled between two points without the use of protective raceways. In these applica-
tions, the cable usually includes a tough outer jacket. The dual (duplex or zip cord)
type of cable is also used for patch cords, user cords, and jumpers. At the intercon-
nection location for a multistrand tight-buffer cable, you must be careful to provide
proper strain relief for the main cord and the individually connectorized fibers. In
many cases, the jacketed cable is very stiff, while the bare fibers are extremely flex-
ible, yet quite fragile.
