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Speaker 1: Y dot com. Mosey, It's always there. Welcome to brain
Speaker 1: Stuff from how Stuff Works dot com where smart Happens
Speaker 1: h I am Marshall Brain with today's question, how does
Speaker 1: a fiber optic cable work? Over the last thirty years
Speaker 1: or so, fiber optic cables have taken over and transformed
Speaker 1: the long distance telephone industry. Optical fibers are also a
Speaker 1: huge part of making the Internet available around the world.
Speaker 1: When fiber replaces copper for long distance calls and Internet traffic,
Speaker 1: it dramatically lowers costs. To understand how a fiber optic
Speaker 1: cable works, imagine an immensely long drinking straw or flexible
Speaker 1: plastic pipe. For example, imagine a pipe that's several miles long.
Speaker 1: Now imagine that the inside surface of the pipe has
Speaker 1: been coated with a perfect mirror. Now imagine that you
Speaker 1: are looking into one end of the pipe several miles away.
Speaker 1: At the other end, a friend turns on a flashlight
Speaker 1: and shines it into the pipe. Because the interior of
Speaker 1: the pipe is a perfect mirror, the flashlights light will
Speaker 1: reflect off the sides of the pipe, even though the
Speaker 1: pipe may curve and twist, and you will see the
Speaker 1: light at the other end. If your friend were to
Speaker 1: turn the flashlight on and off in a Morse code fashion,
Speaker 1: your friend could communicate with you through this pipe. That
Speaker 1: is the essence of a fiber optic cable. Making a
Speaker 1: cable out of a mirror tube would work, but it
Speaker 1: would be bulky and it would be very hard to
Speaker 1: coat the interior of the tube with a perfect mirror.
Speaker 1: A real fiber optic cable is therefore made out of glass.
Speaker 1: The glass is incredibly pure, so that even though it's
Speaker 1: several miles long, light can still make it through. Imagine
Speaker 1: glass so transparent that a window several miles sticks still
Speaker 1: looks clear. The glass is drawn into a very thin
Speaker 1: strand with a thickness comparable to that of a human hairror.
Speaker 1: The glass strand is then coated in several layers of plastic.
Speaker 1: By coating the glass in plastic, you get the equivalent
Speaker 1: of a mirror around the glass. Strand this mirror creates
Speaker 1: total internal reflection, just like a perfect mirror coating on
Speaker 1: the inside of a tube does. You can experience this
Speaker 1: sort of reflection with a flashlight and a window in
Speaker 1: a dark room. If you direct the flashlight through the
Speaker 1: window at a ninety degree angle, it passes straight through
Speaker 1: the glass. However, if you shine the flashlight at a
Speaker 1: very shallow angle nearly parallel to the glass, the glass
Speaker 1: will act as a mirror and you will see the
Speaker 1: beam reflect off the window and hit the wall opposite
Speaker 1: on the inside of the room. Light traveling through the
Speaker 1: fiber bounces at shallow angles like this and stays completely
Speaker 1: within the fiber. To send telephone conversations through a fiber
Speaker 1: optic cable, analog voice signals are translated into digital signals.
Speaker 1: A laser at one end of the pipe switches on
Speaker 1: and off to send each bit. Modern fiber systems with
Speaker 1: a single laser can transmit billions of bits per second.
Speaker 1: The laser can turn on and off several billion times
Speaker 1: per second. The newest systems use lasers with multiple colors
Speaker 1: to fit multiple signals into the same fiber. Modern fiber
Speaker 1: optic cables can carry a signal quite a distance, perhaps
Speaker 1: sixty miles or a hundred kilometers. On a long distance line,
Speaker 1: there is an equipment hut every forty or fifty miles.
Speaker 1: The hut contains equipment that picks up and retransmits the
Speaker 1: signal down the next segment at full strength. Do you
Speaker 1: have any ideas or suggestions for this podcast? If so,
Speaker 1: please send me an email at podcast at how stuff
Speaker 1: works dot com. For more on this and thousands of
Speaker 1: other topics, go to how stuffs dot com and be
Speaker 1: sure to check out the brain stuff blog on the
Speaker 1: house stuff works dot com home page. Protect your organization's
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