David goes to
AT&T's Bell
Laboratories to
learn about the
ever-changing
world of tele-
communications.
New Frontiers in Electronic Communications
Alexander Graham Bell invented a talking machine that used pulses of electricity to carry sound through copper wires and called it the telephone. Soon after, he tested the photophone, another talking machine that used a beam of sunlight to carry voices from one place to another. Although he had high hopes for the future of his photophone, it depended on a constant source of sunlight and proved to be impractical.
Not until the invention of lasers and optical fibers did Bell's dream come true. In the mid-1970s, researchers began pumping pulses of laser light through thin glass fibers to move information. Light is actually a sequence of vibrations. Scientists discovered how to vary these patterns of vibrations and convey information. When a conversation occurs over a telephone system that uses optical fibers, the vibrations of your voice are converted to the pattern of the laser. At the other end, these variations are turned back into sound.
Because lasers can be modulated with highly complex patterns much greater quantities of information can be transmitted. Stringing electrical cables or optical fiber cables from place to place is very expensive. Because the new optical fibers can handle so much more information than traditional telephone wires, it has become more economical to replace conventional wires with the new technology.
And, fiber-optic communications are not limited to telephone conversations. They can even be used to transmit complex information, like television or data between computers. As fiber-optic cables interconnect our area, it will be possible to see and purchase items from distant stores, participate in classes or meetings happening across the world, see people you're talking to on the telephone and have instant access to the latest information stored in libraries, all without leaving your home!
Other industries benefit from fiber optics. Physicians use them to examine areas of the body instead of performing surgery. In industry, fiber optics aid workers in repairing jet engines, nuclear reactors and other complicated machinery. In the future, fiber optics will be used to control lighting, heating, air conditioning, security systems and other types of machinery. The most interesting uses of fiber optics are yet dreamed about!
Laser--Light Amplification by Stimulated Emission of Radiation. A device which produces a light which is highly directional and travels in a narrow beam.
Optical Fibers--Strands of material through which light can travel; analogous to the way water travels through a hose.
Fiber Optics--A branch of physics based on transmission of light through fibers of glass or plastic.
Modulate--To vary the amplitude, frequency or phase of a carrier wave or signal in telephony, telegraphy, radio or television.
Amazing Liquid Light
Light always travels in a straight line, doesnt it?
Main Activity
Light does travel in a straight line but there are times when it doesn't. Light can be inside a curving stream of water because the path of the light changes direction as it is reflected internally by the water. Discover how fiber optics use this principle.
Materials:
1. Make two holes in the jar lid with the hammer and the nail. Make a large hole near one edge and a smaller hole near the opposite edge.
2. Fill the jar three quarters full with water.
3. Turn on the flashlight and hold it to the bottom of the jar so the light shines into the jar.
4. Wrap the jar and the flashlight together in the newspaper. Leave the lid of the jar uncovered. Be careful not to spill the water. If needed, place tape over the holes until the pieces are wrapped together.
5. Now get ready to "pour" light. Turn the lights off and tilt the jar so the water flows out the largest hole into a large container.
Questions
1. What happens if you stick your finger in the water stream near the jar? Down further on the stream?
2. Was the light contained in the stream or did it shine out like a lamp?
3. What would the light look like if you used colored water?
4. How is the curved flow of the water similar to light pulses in fiber optics? What are the differences?
5. What does total internal reflection mean?
Lasers are used all around us. Find as many of their uses as you can. Where
are lasers used in the supermarket? Ask your doctor about laser surgery.
How is it different than standard surgery? Try to attend a laser light
show to see energy waves become art.
Laser light is contained in an optical fiber because of internal reflection.
A periscope uses the same principle but with mirrors instead of optic fibers.
How could you use two mirrors to look around a corner?
Investigate ways light is used in communication. Learn more about Morse
code and see if you and your friends can send messages to each other in
the dark with a flashlight. How are holograms created?
Energy moves from one place to another in waves. Tie a long piece of rope
to a tree or a pole. Make your own waves by shaking the rope up and down.
What energy moves when you shake the rope? What other materials could you
use to make waves? (See the Newton's Apple "Slinky Physics" for
extra hints!) Light waves are the fastest waves we know about. How fast
do light waves from the Sun travel to the Earth?
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Newton's Apple is a production of KTCA Twin Cities Public Television. Made
possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.