Page 77 - Optical Communications Essentials

Source: Optical Communications Essentials

Chapter
5

Optical Fiber Cables

Optical cables are essential elements of an optical communications link. In addi-
tion to providing protection to the optical fibers contained within the cable, the
construction of an optical cable determines whether it can withstand the envi-
ronments in which it will be used. If engineers select the wrong cable configu-
ration, the cost of retrofitting installed cable can be prohibitively high (and
afterward the engineers may be told to seek employment elsewhere). When a
circuit card fails or an equipment rack needs replacement, it is a fairly straight-
forward process to enter an equipment room to remove the items and put in
new ones. Optical cables, on the other hand, cannot be replaced easily without
undergoing major disruptive digging or having huge piles or spools of cables
lying in the way in hallways or on sidewalks. This chapter addresses cabling
design considerations, cable types for diverse applications, and installation
methods in different environments.

5.1. Fiber-Related Design Issues
Cabling of optical fibers involves enclosing them within some type of protective
structure. The cable structure will vary greatly depending on whether the cable
is to be pulled or blown into underground or intrabuilding tubes (called ducts),
buried directly in the ground, installed on outdoor poles, or placed underwater.
Different cable configurations are required for each type of application, but cer-
tain fundamental cable design principles will apply in every case. The objectives
of cable manufacturers have been that the optical fiber cables should be instal-
lable with the same type of equipment, installation techniques, and precautions
as those used for conventional wire cables. This requires special cable designs
because of the unique properties of optical fibers such as their strength, dielec-
tric (nonmetallic) nature, small size, and low weight. Let’s take a closer look at
these properties.
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