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Fiber optics

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.

5.5. Fiber Optics and Optoelectronics, Second Edition, Peter K. Cheo, Prentice Hall,

Englewood Cliffs, New Jersey, 1990.

Source: Essay UK - https://www.essay.uk.com



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