Page 87 - Optical Communications Essentials

Optical Fiber Cables

Optical Fiber Cables 77

Alternatively, a cable for an aerial application does not contain a built-in mes-
senger. Instead, first a separate steel messenger is strung between poles, and
then the optical cable is lashed to this messenger. This lashing method supports
the cable at short intervals between poles instead of just at the poles them-
selves, thereby reducing stress along the length of the cable.

5.4.2. Armored cable
An armored cable for direct-burial or underground duct applications has one or
more layers of steel-wire or steel-sheath protective armoring below a layer of
polyethylene (PE) jacketing, as shown in Fig. 5.9. This not only provides addi-
tional strength to the cable but also protects it from gnawing animals such as
squirrels or burrowing rodents. Since burrowing gophers do not drink (not even
water), they often cause damage to underground cables, which to them look like
tasty roots that contain food and moisture. For example, in the United States
the plains pocket gopher (Geomys busarius) will destroy unprotected cable that
is buried less than 6ft deep.

5.4.3. Underwater cable
Underwater cable, also known as submarine cable, can be used in rivers, lakes,
and ocean environments. Since such cables normally are exposed to high water
pressures, they have much more stringent requirements than underground
cables. For example, as shown in Fig. 5.10 for a cable that can be used in rivers
and lakes, they have various water-blocking layers and a heavier armor jacket.
Cables that run under the ocean have further layers of armoring and contain
copper wires to provide electric power for submersed optical amplifiers or regen-
erators. In addition, if such a cable is damaged, the ruptured portion needs to
be lifted to the surface for repair.

Figure 5.9. Example of an armored outdoor cable.

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