Fiber-optics

The invention: The application of glass fibers to electronic communications
and other fields to carry large volumes of information
quickly, smoothly, and cheaply over great distances.
The people behind the invention:
Samuel F. B. Morse (1791-1872), the American artist and
inventor who developed the electromagnetic telegraph
system
Alexander Graham Bell (1847-1922), the Scottish American
inventor and educator who invented the telephone and the
photophone
Theodore H. Maiman (1927- ), the American physicist and
engineer who invented the solid-state laser
Charles K. Kao (1933- ), a Chinese-born electrical engineer
Zhores I. Alferov (1930- ), a Russian physicist and
mathematician
The Singing Sun
In 1844, Samuel F. B. Morse, inventor of the telegraph, sent his famous
message, “What hath God wrought?” by electrical impulses
traveling at the speed of light over a 66-kilometer telegraph wire
strung between Washington, D.C., and Baltimore. Ever since that
day, scientists have worked to find faster, less expensive, and more
efficient ways to convey information over great distances.
At first, the telegraph was used to report stock-market prices and
the results of political elections. The telegraph was quite important
in the American Civil War (1861-1865). The first transcontinental
telegraph message was sent by Stephen J. Field, chief justice of the
California Supreme Court, to U.S. president Abraham Lincoln on
October 24, 1861. The message declared that California would remain
loyal to the Union. By 1866, telegraph lines had reached all
across the North American continent and a telegraph cable had
been laid beneath the Atlantic Ocean to link the OldWorld with the
New World.Another American inventor made the leap from the telegraph to
the telephone. Alexander Graham Bell, a teacher of the deaf, was interested
in the physical way speech works. In 1875, he started experimenting
with ways to transmit sound vibrations electrically. He realized
that an electrical current could be adjusted to resemble the vibrations of speech. Bell patented his invention on March 7, 1876.
On July 9, 1877, he founded the Bell Telephone Company.
In 1880, Bell invented a device called the “photophone.” He used
it to demonstrate that speech could be transmitted on a beam of
light. Light is a form of electromagnetic energy. It travels in a vibrating
wave. When the amplitude (height) of the wave is adjusted, a
light beam can be made to carry messages. Bell’s invention included
a thin mirrored disk that converted sound waves directly into a
beam of light. At the receiving end, a selenium resistor connected to
a headphone converted the light back into sound. “I have heard a
ray of sun laugh and cough and sing,” Bell wrote of his invention.
Although Bell proved that he could transmit speech over distances
of several hundred meters with the photophone, the device
was awkward and unreliable, and it never became popular as the
telephone did. Not until one hundred years later did researchers find
important practical uses for Bell’s idea of talking on a beam of light.
Two other major discoveries needed to be made first: developdevelopment
of the laser and of high-purity glass. Theodore H. Maiman, an
American physicist and electrical engineer at Hughes Research Laboratories
in Malibu, California, built the first laser. The laser produces
an intense, narrowly focused beam of light that can be adjusted to
carry huge amounts of information. The word itself is an acronym for
light amplification by the stimulated emission of radiation.
It soon became clear, though, that even bright laser light can be
broken up and absorbed by smog, fog, rain, and snow. So in 1966,
Charles K. Kao, an electrical engineer at the Standard Telecommunications
Laboratories in England, suggested that glass fibers could
be used to transmit message-carrying beams of laser light without
disruption from weather.
Fiber Optics Are Tested
Optical glass fiber is made from common materials, mostly silica,
soda, and lime. The inside of a delicate silica glass tube is coated
with a hundred or more layers of extremely thin glass. The tube is
then heated to 2,000 degrees Celsius and collapsed into a thin glass
rod, or preform. The preform is then pulled into thin strands of fiber.
The fibers are coated with plastic to protect them from being nicked
or scratched, and then they are covered in flexible cable.The earliest glass fibers
contained many impurities
and defects, so they did not
carry light well. Signal repeaters
were needed every
few meters to energize
(amplify) the fading pulses
of light. In 1970, however,
researchers at the Corning
Glass Works in New York
developed a fiber pure
enough to carry light at
least one kilometer without
amplification.
The telephone industry
quickly became involved in the new fiber-optics technology. Researchers
believed that a bundle of optical fibers as thin as a pencil
could carry several hundred telephone calls at the same time. Optical
fibers were first tested by telephone companies in big cities,
where the great volume of calls often overloaded standard underground
phone lines.
On May 11, 1977, American Telephone & Telegraph Company
(AT&T), along with Illinois Bell Telephone, Western Electric, and
Bell Telephone Laboratories, began the first commercial test of fiberoptics
telecommunications in downtown Chicago. The system consisted
of a 2.4-kilometer cable laid beneath city streets. The cable,
only 1.3 centimeters in diameter, linked an office building in the
downtown business district with two telephone exchange centers.
Voice and video signals were coded into pulses of laser light and
transmitted through the hair-thin glass fibers. The tests showed that
a single pair of fibers could carry nearly six hundred telephone conversations
at once very reliably and at a reasonable cost.
Six years later, in October, 1983, Bell Laboratories succeeded in
transmitting the equivalent of six thousand telephone signals through
an optical fiber cable that was 161 kilometers long. Since that time,
countries all over the world, fromEngland to Indonesia, have developed
optical communications systems.Consequences
Fiber optics has had a great impact on telecommunications. Asingle
fiber can now carry thousands of conversations with no electrical
interference. These fibers are less expensive, weigh less, and take up
much less space than copper wire. As a result, people can carry on
conversations over long distances without static and at a low cost.
One of the first uses of fiber optics and perhaps its best-known
application is the fiberscope, a medical instrument that permits internal
examination of the human body without surgery or X-ray
techniques. The fiberscope, or endoscope, consists of two fiber
bundles. One of the fiber bundles transmits bright light into the patient,
while the other conveys a color image back to the eye of the
physician. The fiberscope has been used to look for ulcers, cancer,
and polyps in the stomach, intestine, and esophagus of humans.
Medical instruments, such as forceps, can be attached to the fiberscope,
allowing the physician to perform a range of medical procedures,
such as clearing a blocked windpipe or cutting precancerous
polyps from the colon.