Essay/Term paper: Fiber optics

Essay, term paper, research paper:  Information Technology

Fiber Optics


Fiber Optic Cable Facts

"A relatively new technology with vast potential importance, fiber optics is the
channeled transmission of light through hair-thin glass fibers."

[ Less expensive than copper cables

[ Raw material is silica sand

[ Less expensive to maintain If damaged, restoration time is faster
(although more users are affected)

[ Backbone to the Information Superhighway

Information (data and voice) is transmitted through the fiber digitally by
the use of high speed LASERs (Light Amplification through the Simulated Emission
of Radiation) or LEDs (Light Emitting Diodes). Each of these methods create a
highly focused beam of light that is cycled on and off at very high speeds.
Computers at the transmitting end convert data or voice into "bits" of
information. The information is then sent through the fiber by the presence, or
lack, of light. Computers on the receiving end convert the light back into data
or voice, so it can be used.

ORIGIN OF FIBER OPTICS

Information (data and voice) is transmitted through the fiber digitally by
the use of high speed LASERs (Light Amplification through the Simulated Emission
of Radiation) or LEDs (Light Emitting Diodes). Each of these methods create a
highly focused beam of light that is cycled on and off at very high speeds.
Computers at the transmitting end convert data or voice into "bits" of
information. The information is then sent through the fiber by the presence, or
lack, of light. So, all of the data is sent light pulses. Computers on the
receiving end convert the light back into data or voice, so it can be used.

All of this seems to be a very "modern" concept, and the technology we use
is. The concept though, was the idea of Alexander Graham Bell in the late 1800's.
He just didn't have a dependable light source... some days the sun doesn't
shine! He thought of the idea that our voices could be transmitted by pulses of
light. The people who thought that audio, video, and other forms of data could
be transmitted by light through cables, were present day scientists. Most of
the things that are possible today, Alexander Grahm Bell could never even have
dreamed of.

Although the possibility of lightwave communications occurred to Alexander
Graham Bell (who invented the telephone), his ideas couldn't be used until the
LASER or LED had been invented. Most of these advances occurred in the 1970s,
and by 1977 glass-purifying and other fiber-optic manufacturing techniques had
also reached the stage where interoffice lightwave communications were possible.
With further technological development, many intercity routes were in operation
by 1985, and some transoceanic routes had been completed by 1990. Now, in the
mid-90's, worldwide connections are possible through the Internet.

The light is prevented from escaping the fiber by total internal
reflection, a process that takes place when a light ray travels through a medium
with an Index of Refraction higher than that of the medium surrounding it. Here
the fiber core has a higher refractive index than the material around the core,
and light hitting that material is reflected back into the core, where it
continues to travel down the fiber.

THE PROPAGATION OF LIGHT AND LOSS OF SIGNALS

The glass fibers used in present-day fiber-optic systems are based on
ultrapure fused silica (sand). Fiber made from ordinary glass is so dirty that
impurities reduce signal intensity by a factor of one million in only about 16
ft of fiber. These impurities must be removed before useful long-haul fibers can
be made. But even perfectly pure glass is not completely transparent. It weakens
light in two ways. One, occurring at shorter wavelengths, is a scattering caused
by unavoidable density changes within the fiber. In other words, when the light
changes mediums, the change in density causes interference. The other is a
longer wavelength absorption by atomic vibrations. For silica, the maximum
transparency, occurs in wavelengths in the near infrared, at about 1.5 m
(micrometers).

APPLICATIONS

Fiber-optic technology has been applied in many areas, although its
greatest impact has come in the field of telecommunications, where optical fiber
offers the ability to transmit audio, video, and data information as coded light
pulses. Fiber optics are also used in the field of medicine, all of the wire-
cameras and lights are forms of fiber optic cable. In fact, fiber optics have
quickly become the preferred mode of transmitting communications of all kinds.
Its advantages over older methods of transmitting data are many, and include
greatly increased carrying capacity (due to the very high frequency of light),
lower transmission losses, lower cost of basic materials, much smaller cable
size, and almost complete immunity to any interference. Other applications
include the simple transmission of light for illumination in awkward places,
image guiding for remote viewing, and sensing.

ADVANTAGES OF FIBER OPTIC CABLE

This copper cable contains 3000 individual wires.

It takes two wires to handle one two-way conversation.

That means 1500 calls can be transmitted simultaneously on each cable.

Each fiber optic cable contains twelve fiber wires.

Two fibers will carry the same number of simultaneous conversations as one whole
copper cable.

Therefore, this fiber cables replace six of the larger ones.

And 90,000 calls can be transmitted simultaneously on one fiber optic cable.

LONG DISTANCE

FIBER-OPTIC COMMUNICATIONS SYSTEMS

AT&T's Northeast Corridor Network, which runs from Virginia to
Massachusetts, uses fiber cables carrying more than 50 fiber pairs. Using a
semiconductor LASER or a light-emitting diode (LED) as the light source, a
transmitter codes the audio or visual input into a series of light pulses,
called bits. These travel along a fiber at a bit-rate of 90 million bits per
second (or 90 thousand kbps). Pulses need boosting, about every 6.2 miles, and
finally reach a receiver, containing a semiconductor photodiode detector (light
sensor), which amplifies, decodes, and regenerates the original audio or visual
information. Silicon integrated circuits control and adjust both transmitter and
receiver operations.

THE FUTURE OF FIBER OPTICS

Light injected into a fiber can adopt any of several zigzag paths, or modes.
When a large number of modes are present they may overlap, for each mode has a
different velocity along the fiber. Mode numbers decrease with decreasing fiber
diameter and with a decreasing difference in refractive index between the fiber
core and the surrounding area. Individual fiber production is quite practical,
and today most high-capacity systems use single fibers. The present pace of
technological advance remains impressive, with the fiber capacity of new systems
doubling every 18 to 24 months. The newest systems operate at more than two
billion bits per second per fiber pair. During the 1990s optical fiber
technology is expected to extend to include both residential telephone and cable
television service.

Currently Bell South is placing fiber cables containing up to 216 fibers,
and manufacturers are starting to build larger ones. Bell South has been
placing fiber cables in the Orlando area since the early 1980s, and currently
has hundreds of miles in service to business and residential customers.

BIBLIOGRAPHY

1. 1995 Grolier Multimedia Encyclopedia, Grolier Electronic Publishing, Inc.

2. 1994 Compton's Interactive Encyclopedia, Compton's NewMedia.

3. Fiber Optics abd Lightwave Communications Standard Dictionary, Martin H.
Weik, D.Sc., Van Nostrand Reinhold Company, New York, New York, 1981.

4. Fiber Optics and Laser Handbook, 2nd Edition, Edward L. Stafford, Jr. and
John A. McCann, Tab Books, Inc., Blue Ridge Summit, Pennsylvania, 1988.

5. Fiber Optics and Optoelectronics, Second Edition, Peter K. Cheo, Prentice
Hall, Englewood Cliffs, New Jersey, 1990.