WEBVTT - How does a fiber optic cable work?

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<v Speaker 1>Y dot com. Mosey, It's always there. Welcome to brain

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<v Speaker 1>Stuff from how Stuff Works dot com where smart Happens

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<v Speaker 1>h I am Marshall Brain with today's question, how does

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<v Speaker 1>a fiber optic cable work? Over the last thirty years

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<v Speaker 1>or so, fiber optic cables have taken over and transformed

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<v Speaker 1>the long distance telephone industry. Optical fibers are also a

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<v Speaker 1>huge part of making the Internet available around the world.

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<v Speaker 1>When fiber replaces copper for long distance calls and Internet traffic,

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<v Speaker 1>it dramatically lowers costs. To understand how a fiber optic

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<v Speaker 1>cable works, imagine an immensely long drinking straw or flexible

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<v Speaker 1>plastic pipe. For example, imagine a pipe that's several miles long.

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<v Speaker 1>Now imagine that the inside surface of the pipe has

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<v Speaker 1>been coated with a perfect mirror. Now imagine that you

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<v Speaker 1>are looking into one end of the pipe several miles away.

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<v Speaker 1>At the other end, a friend turns on a flashlight

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<v Speaker 1>and shines it into the pipe. Because the interior of

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<v Speaker 1>the pipe is a perfect mirror, the flashlights light will

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<v Speaker 1>reflect off the sides of the pipe, even though the

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<v Speaker 1>pipe may curve and twist, and you will see the

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<v Speaker 1>light at the other end. If your friend were to

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<v Speaker 1>turn the flashlight on and off in a Morse code fashion,

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<v Speaker 1>your friend could communicate with you through this pipe. That

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<v Speaker 1>is the essence of a fiber optic cable. Making a

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<v Speaker 1>cable out of a mirror tube would work, but it

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<v Speaker 1>would be bulky and it would be very hard to

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<v Speaker 1>coat the interior of the tube with a perfect mirror.

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<v Speaker 1>A real fiber optic cable is therefore made out of glass.

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<v Speaker 1>The glass is incredibly pure, so that even though it's

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<v Speaker 1>several miles long, light can still make it through. Imagine

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<v Speaker 1>glass so transparent that a window several miles sticks still

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<v Speaker 1>looks clear. The glass is drawn into a very thin

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<v Speaker 1>strand with a thickness comparable to that of a human hairror.

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<v Speaker 1>The glass strand is then coated in several layers of plastic.

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<v Speaker 1>By coating the glass in plastic, you get the equivalent

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<v Speaker 1>of a mirror around the glass. Strand this mirror creates

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<v Speaker 1>total internal reflection, just like a perfect mirror coating on

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<v Speaker 1>the inside of a tube does. You can experience this

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<v Speaker 1>sort of reflection with a flashlight and a window in

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<v Speaker 1>a dark room. If you direct the flashlight through the

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<v Speaker 1>window at a ninety degree angle, it passes straight through

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<v Speaker 1>the glass. However, if you shine the flashlight at a

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<v Speaker 1>very shallow angle nearly parallel to the glass, the glass

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<v Speaker 1>will act as a mirror and you will see the

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<v Speaker 1>beam reflect off the window and hit the wall opposite

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<v Speaker 1>on the inside of the room. Light traveling through the

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<v Speaker 1>fiber bounces at shallow angles like this and stays completely

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<v Speaker 1>within the fiber. To send telephone conversations through a fiber

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<v Speaker 1>optic cable, analog voice signals are translated into digital signals.

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<v Speaker 1>A laser at one end of the pipe switches on

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<v Speaker 1>and off to send each bit. Modern fiber systems with

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<v Speaker 1>a single laser can transmit billions of bits per second.

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<v Speaker 1>The laser can turn on and off several billion times

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<v Speaker 1>per second. The newest systems use lasers with multiple colors

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<v Speaker 1>to fit multiple signals into the same fiber. Modern fiber

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<v Speaker 1>optic cables can carry a signal quite a distance, perhaps

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<v Speaker 1>sixty miles or a hundred kilometers. On a long distance line,

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<v Speaker 1>there is an equipment hut every forty or fifty miles.

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<v Speaker 1>The hut contains equipment that picks up and retransmits the

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<v Speaker 1>signal down the next segment at full strength. Do you

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<v Speaker 1>have any ideas or suggestions for this podcast? If so,

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<v Speaker 1>please send me an email at podcast at how stuff

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<v Speaker 1>works dot com. For more on this and thousands of

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