Introduction
In recent years Fiber Optics has steadily replaced copper wire as
the appropriate means of communication signal transmission. Fiber
spans long distances between local phone systems as well as provides
the backbone for many network systems. Other system users include
university campuses, office buildings, industrial plants, and electric
utility companies. Fiber is now making its way into residential communities
also known as the "last mile". As the bandwidth requirements
increase for residential users, fiber optic "last mile"
networks will become more and more the norm rather than the exception.
Today there are only a handful of Fiber to the Home (FTTH) networks
deployed across the country, however the number is beginning to rapidly
increase. Homeowners that are connected to these networks will share
the distinction and advantage in their ability to obtain the latest
and best broadband services.
Fiber-Optic Technology
A Fiber Optic system is similar to the copper wire system that Fiber
Optics is replacing. The difference is that Fiber Optics use light
pulses to transmit information down fiber lines instead of using electronic
pulses to transmit information down copper lines. Looking at the components
in a Fiber Optic chain will give a better understanding of how the
system works in conjunction with wire based systems.
 At
one end of the system is a transmitter. This is the place of origin
for information coming on to Fiber Optic lines. An injection-laser
diode (ILD) can be used for generating the light pulses. Using a lens,
the light pulses are funneled into the Fiber Optic medium where they
transmit themselves down the line.
Light pulses move easily down the Fiber Optic line
because of a principle known as total internal reflection. "This
principle of total internal reflection states that when the angle
of incidence exceeds a critical value, light cannot get out of the
glass; instead, the light bounces back in. When this principle is
applied to the construction of the Fiber Optic strand, it is possible
to transmit information down fiber lines in the form of light pulses.
There are generally five elements that make up the construction
of a Fiber Optic strand, or cable: the optic core, optic cladding,
a buffer material, a strength material and the outer jacket (Fig.
1). The optic core is the light-carrying element at the center of
the optical fiber. It is commonly made from a combination of silica
and germania. Surrounding the core is the optic cladding made of
pure silica . It is this combination that makes the principle of
total internal reflection possible. The difference in materials
used in the making of the core and the cladding creates an extremely
reflective surface at the point in which they interface. Light pulses
entering the fiber core reflect off the core/cladding interface
and thus remain within the core as they move down the line.
Fig. 1. Cut away of a Fiber Optic cable.
Surrounding the cladding is a buffer material used to help shield
the core and cladding from damage. A strength material surrounds
the buffer, preventing stretch problems when the fiber cable is
being pulled. The outer jacket is added to protect against abrasion,
solvents, and other contaminants.
Once the light pulses reach their destination they are channeled
into the optical receiver. "The basic purpose of an optical
receiver is to detect the received light incident on it and to convert
it to an electrical signal containing the information impressed
on the light at the transmitting end. The electronic information
is then ready for input into electronic based communication devices,
such as a computer, telephone, or TV.
Fiber-Optic Applications
The use of Fiber Optics was generally not available until 1970 when
Corning Glass Works was able to produce a fiber with a loss of 20
dB/km. That is, 1% of the light would remain after traveling 1 km.
It was recognized that optical fiber would be feasible for telecommunication
transmission only if glass could be developed so pure that attenuation
would be 20 dB/km or less. Today's optical fiber attenuation ranges
from 0.5 dB/km to 1000 dB/km depending on the optical fiber used.
Attenuation limits are based on intended application.
The applications of optical fiber communications have increased
at a rapid rate, since the first commercial installation of a Fiber
Optic system in 1977. Telephone companies began early on, replacing
their old copper wire systems with optical fiber lines. Today's
telephone companies use optical fiber throughout their system as
the backbone architecture and as the long-distance connection between
city phone systems.
Local Area Networks (LAN) is a collective group of computers, or
computer systems, connected to each other allowing for shared program
software or databases. Colleges, universities, office buildings,
and industrial plants, just to name a few, all make use of optical
fiber within their LAN systems.
Power companies utilize Fiber Optics in their communication systems
and most already have Fiber Optic communication systems in use for
monitoring their power grid systems.
Fiber-Optic Advantages
There are several advantages that have been established with the
development and implementation of Fiber Optic cable systems. Compared
to copper, optical fiber is relatively small in size and light in
weight. This characteristic has made it desirable as intra-floor
conduits and wiring duct space has become increasing plugged with
expanded copper cable installation.
Optical fiber is also desirable because of its electromagnetic immunity.
Since Fiber Optics use light to transmit a signal, it is not subject
to electromagnetic interference, radio frequency interference, or
voltage surges. This may be an important consideration when laying
cables near electronic hardware such as computers or industrial
equipment. As well, since it does not use electrical impulses, it
does not produce electric sparks which can be an obvious fire hazard.
Advances in optical fiber technology have led to decreases in signal
loss, or attenuation. As an electric pulse or a light pulse travels
down its respective cable line, it will eventually lose signal energy
due to imperfections in the transmission medium. To keep the signal
going, it must be boosted every so often along the medium line.
A signal regenerator is used to boost the electronic pulse in a
copper cable. An optical repeater or amplifier is used to boost
the light pulse in a Fiber Optic cable. The advantage of optical
fiber is that it performs better with respect to attenuation. Fiber-optic
cable needs fewer boosting devices, along the same length of line,
than copper cable.
A characteristic feature of optical fiber is its wide bandwidth.
Bandwidth refers to the amount of information that a fiber can carry.
The greater the bandwidth, the greater the carrying capacity of
the optical fiber.
Summary
Based on industry activity, it is evident that Fiber Optics has
become the industry standard for transmission of telecommunication
information. The next progressive step for Fiber Optics is into
residential communities also referred to as the "Last Mile",
with the ultimate phase of Fiber Optic deployment directly to the
home. The choice is not whether to convert to optical fiber, but
rather when to convert to optical fiber.
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