standards set requirements up to 250 MHz. These standards not only apply to
the cable but also to all connector and cable termination devices such as the
cable jacks, patch cords, and the patch panel. Many manufacturers test and/
or manufacture cable beyond the standards to differentiate their product as
going beyond the standards.
Fiber Optic Cable
Fiber optic cables use strands of glass to propagate light. The light pulses
transport communication signals between devices. At the center of the fiber
optic strand is a small inner core that carries the propagated light. Surround-
ing the core is the outer cladding. Both the core and the cladding are glass but
have different “refractive indexes” which essentially means that light travels at
different speeds through the materials. The result is that light pulses produced
from lasers or LEDs at one end of a fiber optic cable are sent through the fiber
optic core and are reflected back to the core when the light hits the fiber optic
cladding, thus keeping the light within the center core.
Fiber optic cables with small inner cores (10 microns or less) have only one
path for the light and are referred to as single-mode fiber. Fiber optic cables
with slightly larger cores (50 and 62.5 microns) have multiple paths for the
light and are referred to as multimode fiber. The cladding of both types of
fiber is 125 microns (Fig. 2.5). For comparison, human hair is generally in
Figure 2.5 Fiber optic cable.
The Foundations of a Smart Building 15