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| The Basics to Fiber Optics                   by: Tradeser |
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Sections
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1. What Is Fibers Optics?
2. Where Are Optical Fibers Used?
3. How Are Optical Fibers Made?
4. How do Optical Fibers Work?
5. Morse Code    
6. ASCII-8
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Where Are Optical Fibers Used?
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Two inventions on the 1960s and 1970s made fiber optics possible.
During this time, scientist invented lasers. Lasers are powerful
sources of a special kind of light. Other researchers developed
optical fibers.

An optical fiber is a flexible thread of a very clear glass--thinner
than a cat's whisker and up to six miles long. Laser lights can
pass through the length of optical fiber ans still shine bright.
Because optical fibers can serve as pipelines for light, they also
are called light guides.

In the mid-1970s, these inventions were teamed together. Now pulses
of light flash through optical fibers carrying information and
messages over great distances. This important new technology is
called fiber optics.

Glass fiber are replacing copper wires for may reasons. The fiber are
replacing copper wires for many reasons. The fibers are not as
expensive for telephone companies to install. They weigh a lot less
than copper wires--making them easier for workers to handle. A single

four-and-one-half-pound spool of optical fiber can carry the same
number of messages as two hundred reels of copper wire that weigh
over sixteen thousand pounds.

The fibers are better, too, because light is not affected by nearby
electrical generators, motors, power lines, or lightning storms. These
are often the causes of noisy static on telephones or information
errors in computers systems connected by copper wires.

As electrical signals pass through copper wire, they become weakened.
Devices called repeaters are used to strengthen the electrical signals
about every mile along each line. In fiber optic systems, repeaters
are needed only every six miles or so to boost the light signal.
Experiments have shown that this distance can be stretched many more
miles.

However, the most important reason for using glass fibers is that they
can carry much more information than copper wires. A single pair of
threadlike glass fibers can transmit thousands of telephone calls at
once. A cable as thick as your arm and containing and containing 256
pairs of copper wires would be needed to handle the same number of
conversations.

Pairs of fiber (or wires) are used for two-way communications. One
fiber carries your voice to the listener at the other end of the line.
The other member of the pair transmits the other person's reply to
you.

Optical fibers are less expensive, easier to install, and more
dependable than copper wires. With light from lasers, they can
transmit thousands of times more information than electricity in copper
wires. The new technology of fiber optics is a better and faster way
to communicate.


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Where Are Optical Fibers Used?
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All over the world, the copper wires of telephone trunk lines
are being replaced be modern glass optical fibers. One of the
first attempts to use an optical fiber system in the United
States was in 1977 in Chicago. There, two offices of the Bell
Telephone Company and a third building for customers were
connected successfully by twenty-four light-carrying glass
fibers. The fibers were threaded through telephone cabled
already under the city streets. The total length of the fibers
was about 1.5 miles.

In 1978, Visa-United Telecommunications at Walt Disney World
near Orlando, Florida, was the first to use fiber optics
commercially in the United States. Telephones throughout the
28,000-acre park are liked by fiber optic trunk lines. Video
transmissions by glass fibers are made to many individual hotel
rooms on the property from one location. Lighting and alarm
systems also use optical fibers.

American Telephone and Telegraph has in service a fiber optic
line that connects Boston, New York City, Washington, D.C.,
and Richmond, Virginia. The truck line is part of a project 780
 miles long. The light cable used is the thickness of garden
hose. Nevertheless, it can carry eighty thousand calls at once.

By July 1988, American Telephone and Telegraph laid a fiber
optic cable beneath the ocean between North America and Europe.
The cable is called TAT-8 because it is AT&T’s eighth
transatlantic telephone cable. TAT-1, a copper cable was
completed in 1956 and could carry fifty-one calls at a time.
TAT-7, the last copper cable, was laid 1983. It can handle about
eight thousand calls at one time. Even With TAT-8, a second fiber
transatlantic cable, TAT-9, probably was put down between
California and Hawaii. Now Satellites are used more for these
communications.

Glass fibers are ideal for military defense. In addition to
their other advantages, the fibers are easy to hide from an enemy.
Metal detectors cannot locate them, for example. Also, the
fibers are almost impossible to secretly tap or jam. [That’s
right almost. Every book I read on fiber optics said "almost"
Gee, I wonder why?]  Thus, vital messages are more likely to 
get through. Light-carrying fibers usually are not affected by 
radiation. And they can be used safely near ammunition storage 
areas of fuel tanks because they do not create sparks as electricity
can in copper wires.

The North American Air Defense Command is located deep inside
Cheyenne Mountain in Colorado. Its computers, linked by
optical fibers, process radar information from around the globe.
Army field communications systems also depend on optical
fibers.


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How Are Optical Fibers Made?
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The glass used to make optical fibers must be very pure. Light 
must be able to pass through the length of the fiber without
being scattered, or losing brightness. Though glass in a 
eyeglass lens look perfect, a three-foot-think piece of this kind
of glass would stop a beam of ordinary light. Tiny particles 
of iron, chromium, copper, and cobalt adsorb or scatter the
light. 

The glass in an optical fiber is nearly free of impurities and
so flawless that light travels through it for many miles. If 
ocean water were as pure, we could be able to see the bottom 
of the Mariana Trench, over thirty-two thousand feet or six
miles down, from the surface of the Pacific.                               

The optical fiber has two parts, a glass inner core, and the 
outside cover cladding. In the core light travels through this
highly transparent part of the fiber. The core of an optical is
surrounded be an outer covering called the cladding. The 
cladding is made of a different type of glass from the sore of 
the fiber. For this reason, the cladding acts like a mirror.
Light traveling through the core of the fiber is reflected back 
into the core by the cladding -- much like a ball bouncing off
the inside of a long pipe. In this way, light entering one end
of an optical fiber is trapped inside the sore until it comes to
the other end.

Optical fibers are manufactured in "clean rooms." The air in 
these rooms is filtered to keep out the tiniest particles of dust. 
Even smallest specks of dirt could ruin the fiber as it is made. 
Workers in these areas usually wear jump suits or lab coats and
caps made from lint free fabric.

An optical fiber start out as a hollow glass tube. The tube is 
mounted on a machine that rotates it. A special gas is fed into the
tube. A flaming torch moves back and forth along the tube, heating
it to nearly 1,600 Celsius. With each pass of the torch, some of 
the hot gas inside forms a fine layer of glass on the inner wall of
the tube. A series of different gases can be fed into the tube. With
this method, layers of several different kinds of glass are 
added to the inside wall. When the addition of glass is complete, 
gas still inside the tube is gently sucked out.

Now, the heat from the torch is increased to 2000 Celsius. The hollow
tube collapses into a solid glass rod called a perform. The 
perform is the size of a broomstick -- about as big around as a 
fifty-cent piece and a yard long.

The perform is cooled and carefully inspected. Light from a laser
used to make sure the core and cladding of the glass preform are
perfect.

Next, the perform is placed in a special furnace where it is heated
to 2,200 C. At this temperature, the tip of the perform can be 
drawn or pulled like taffy into a wisp of an optical fiber -- thinner
than a human hair.

Usually, as soon as it is drawn, the fiber passes through a tiny
funnel where it is coated with fast-drying plastic. The coating 
protects the fiber fro being scratched or damaged.

The fiber from a draw may be up to sic miles long. It is wound onto
a spool for ease of handling and storage. Glass is usually thought 
to be brittle, unbendable, and easily broken. Amazingly, optical 
fibers are flexible and strong as threads of steel. The fiber can 
be tied into loose knots without breaking and light still passes
through from end to end.


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How Do Optical Fibers Work?
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Whenever you talk to someone else the sound of your voice
travels to their ears as a pattern of vibrations or waves
in the air.  Light and electricity also move in waves.

To get an idea what waves look like, tie one end of a long
rope to a post or tree.  Hold the other end of the rope and
walk away until the rope is stretched out, but still slightly
slack.  Now yank the free end of the rope up and down repeatedly.
A series of bumps or waves travels down the rope.

You can change the pattern of the waves.  You can make small
waves by giving weak, up-and-down yanks on the rope.  Or you
can make big waves by giving strong, up-and-down yanks on
the rope.  The height or tallness of the waves depends on the
strength you use to yank the rope up and down.

The distance between the top of one wave and the top of the
next wave is called the wavelength.

Another way to vary the waves is to change their speed. You
can yank the rope up and down only once in a second or many
times in a second.  The number of waves reaching the tree or
post each second is the frequency of the waves.

Why do pulses or waves of light streaking through an optical
fiber go farther, better, and faster than electricity pulsing
through copper wires?

Lasers used in fiber optic systems are made from tiny crystals
of a material called gallium arsenide.  These lasers are as
small as a single grain of salt and easily could fit through
the eye of a needle.  Nevertheless, they can produce some of
the world's most powerful pinpoints of light.

Light from a laser is unlike ordinary light.  Laser light is
all of the same frequency and wavelength.  And all of it is
traveling together in the same direction -- like bullets
aimed from the barrel of a gun at once target. The results
is a brilliant source of very pure light. Laser light can
shine through miles of optical fiber without being boosted as
often as an electrical signal.

The laser light used is fiber optic telephone or communications
systems is infrared. The frequency if infrared light is just
below what people can see with their eyes unaided. Infrared
light is used in communications systems because it can travel
long distances through optical fibers with less loss of power.

Another source of light that is also used with optical fibers for
communications is light emitting diode or LED. LED's are less
costly that gallium arsenide lasers. However, lasers can
transmit more information at high speeds that LED's.

Copper wires can carry a few million electrical pulses each
second. but the number of light pulses as optical fiber can carry
is much greater. It is limited by how many pulses of light each
second today's best lasers can produce. Recent experiments done
at AT&T Bell Laboratories combined the output of several lasers
to achieve as many as 20 billion pulses per second! This far
outshines the number transmitted by copper wires.

How do telephones connected by optical fibers work? In the
mouthpiece of a telephone, the pattern of sound waves of your
voice is first changed into a pattern of waves of electricity
moving through copper wire.  In a fiber optic system, a special
electronic device called an encoder measures samples of the waves
of electricity eight thousand times each second.  Then, each
measurement of the waves is changed into a series of eight ON-OFF
pulses of light.

The pulses of light are a code that stands for the strength or
height of the waves of electricity.  This is called a binary code
because it uses only two signals or digits; zero for when the
light is OFF and one for when the light is ON.  The word "binary"
means two.  Each zero or one is called a binary digit or bit. And
each pulse of ON-OFF light stands for one piece or bit of
information.  Eight bits grouped together are a byte. The specks
of ON-OFF light flash like tiny comets through optical fiber
carrying your message in binary code.  At the other end of the
line is another device called a decoder.  The decoder changes the
pulses of light back into electrical waves.  The receiver of the
telephone then changes the electrical waves back into the sound
waves of your voice.

The coded pulses of light in a fiber optic system can carry so
much information so rapidly that many telephone conversations can
be stacked in an optical fiber. They are then unscrambled at the
other end of the line.

Because a fiber optic system uses coded pulses of ON-OFF light,
it is ideal to link together computers.  Computers "speak" this
binary language.  They not only count in binary, computers also
store and handle huge amounts of information as a code of zeros
and ones.  The entire 2,700 pages of Webster's Unabridged
Dictionary can be transmitted from one computer to another over
optical fibers in six seconds!

Morse Code is a binary code you may already know.  Instead of
zeros and ones, Samuel Morse, used dots and dashes to send any
message by telegraph.  The dots and dashes can stand for any
letter of the alphabet or any decimal number.

Here are two binary codes. One international Mores Code and the
other is a computer code known as the America Standard Code for
Information Interchange or ASCII-8.


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Morse Code    
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	. = DOT
	- = DASH

	.-             A
	-...           B
	-.-.           C
	-..            D
	.              E
	..-.           F
	--.            G
	....           H
	..             I
	.---           J
	-.-            K
	.-..           L
	--             M
	-.             N
	---            O
	.--.           P
	--.-           Q
	.-.            R
	...            S
	-              T
	..-            U
	...-           V
	.--            W
	-..-           X
	--..           Z
	.----          1
	..---          2
	...--          3
	....-          4
	.....          5
	-....          6
	--...          7
	---..          8
	----.          9
	-----          0
	.-.-.-         Period (.)
	--..--         ,
	..--..         ?
	........       Error
	-...-          Double Dash (=)
	---...         :
	-.-.-.         ;
	-.--.          (
	-.--.-         )
	-..-.          /
	.-..-.         "
	...-..-        $
	.----.         '
	.-.-..         Paragraph
	..--.-         Underline (_)
	-.-.-          Start Signal
	.-...          Wait
	.-.-.          End of Message (EOM)
	-.-            Invitation to transmit
	...-.-         End of Work
	...-.          Understood/Acknowledge

	Other Morse signals used

	..-.-          Interrogatory
	....--         Emergency silence
	..-..-         Executive follows
	-----          Break-in
	...---...      Emergency (SOS)
	-..-..-..      Distress signal relay


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ASCII-8
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	11100001       A
	11100010       B
	11100011       C
	11100100       D
	11100101       E
	11100110       F
	11100111       G
	11101000       H
	11101001       I
	11101010       J
	11101011       K
	11101100       L
	11101101       M
	11101110       N
	11101111       O
	11110000       P
	11110001       Q
	11110010       R
	11110011       S
	11110100       T
	11110101       U
	11110110       V
	11110111       W
	11111000       X
	11111010       Z
	01010001       1  
	01010010       2
	01010011       3
	01010100       4	
	01010101       5
	01010110       6
	01010111       7
	01011000       8
	01011001       9
	01010000       0
	01001110       Period (.)
	01011111       ?
	01000001       !
	01001100       ,(comma)
	01000010       "(quotation mark)



Morse Code and ASCII-8 may seem awkward.  But Morse Code made
possible sending messages quickly by telegraph over long distances
as early as 1845.  Today, computers linked by optical fibers can
send vast amounts of any kind of information, including pictures.
And they can do it faster than the human mind can think.