Page 95 - Optical Communications Essentials

Optical Fiber Cables

Optical Fiber Cables 85

messenger wire must be grounded properly and should be kept on one pole side
along the route whenever possible. One of at least three techniques then can be
used to attach the fiber optic cable to the messenger wire. Each of these meth-
ods uses a special lashing machine that hangs on the messenger and attaches
the cable as it moves along the messenger.

5.6.5. Submarine installation
Over a million kilometers of submarine cable already are submerged in oceans
around the world, which is enough to circle the globe 30 times. Specially designed
cable-laying ships are used to install an undersea cable. The ships have several
large circular containers inside of them called cable tanks. In modern cable ships
these tanks together can hold up to 8000km of underwater cable. Such a length
of cable is assembled onshore in a factory environment along with underwater
signal amplifiers that need to be located every 60km or so. The amplifiers are
housed in large beryllium-copper tubes that are about a meter long and 50cm in
diameter. After being assembled, this cable unit is coiled by hand into the cable
holding tanks on the ship at a rate of around 80km/day. During installation, near
the shore a sea plow buries the cable to a depth of about 1m under the ocean
floor to protect it from fishing nets and other factors that might damage the
cable. In the middle of the ocean the cable simply lays exposed on the ocean floor.

5.7. Summary

Optical cables come in many sizes, styles, and configurations. Typically, in addi-
tion to optical fibers they contain aramid yarn or steel strength members and
are encapsulated in one of the jacketing materials listed in Table 5.1. Fibers
within the cable or within a ribbon may be identified individually by means of
the standard color coding method listed in Table 5.3. The three fundamental
cable structures are

■ Tight-buffered fiber cable where each fiber is individually encapsulated within
its own 900-µm-diameter plastic buffer structure
■ Loose-tube cable in which one or more standard coated free-moving fibers are
enclosed in a tube that has an inner diameter which is much larger than the
fiber diameter
■ Ribbon cable where up to 12 fibers are aligned precisely next to one another
and encapsulated in a plastic jacket to form a ribbon
Indoor cables can be used in plenum, riser, and general-purpose areas as
listed in Table 5.2. The different indoor cable types include

■ Interconnect cables for light-duty low-fiber-count indoor applications such as
fiber-to-the-desk links, patch cords, and point-to-point runs in conduits and
trays.

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