ENVS 1200 Chapter Notes - Chapter 19: Coaxial Cable, Optical Fiber
13 May 2018
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ENVS 1200 Chapter 19 Notes – Summary
Introduction
• Coaxial cable is far less susceptible to noise than twisted pair, and is well suited for
relatively long distance connections
• However its cost is significantly higher than twisted pair and its bandwidth is small
compared to fiber
• So its use is fading.
• Fiber-optic cables carry signals in the form of light.
• Optical signals are produced by using the electrical data signal to turn a light on and off
very rapidly.
• A laser or light-emitting diode is used as the light source.
• It is not possible to use a conventional light bulb, because a light bulb cannot be
switched on and off rapidly enough.
• An optical detector at the other end of the cable converts the light signal back to
electrical form.
• The cable itself consists of one or more strands of glass fiber specially designed to carry
waves of light.
• Each strand is thinner than a human hair and may be tens or hundreds of miles long.
• The bundle of fibers is surrounded by a plastic sheath, called cladding, to protect the
fibers.
• Fiber-optic cables are often grouped together in bundles, which are further protected by
an additional tough plastic jacket.
• Light is confined to the fibers, and attenuation is very low.
• Since light is an electromagnetic wave, turning a light on and off is technically a form of
ASK.
• Most users tend to think of fiber-optic transmission as a digital signaling method, for
practical purposes.
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