Season One Research Files
Episode Seventeen
4:00pm-5:00pm
FIBER OPTICS
Fiber optics consists of long, thin strands of optical fibers made of very pure glass that are about the diameter of a human hair. They are arranged in bundles, called optical cables, and used to transmit light signals over long distances. If light is admitted at one end of a fiber, it can travel through the fiber with very low loss of image, even if the fiber is curved.
To understand how a fiber optic cable works, imagine an immensely long drinking straw or flexible plastic pipe. The inside surface of the pipe has been coated with a perfect mirror. If you are looking into one end of the pipe, and several miles away at the other end, someone turns on a flashlight and shines it into the pipe, you will see it at the other end. Because the interior of the pipe is a perfect mirror, the flashlight's light will reflect off the sides of the pipe, even though the pipe may curve and twist.
Making a cable out of a mirrored tube would work, but it would be bulky and it would also be hard to coat the interior of the tube with a perfect mirror. A real fiber optic cable is therefore made out of glass. The glass is incredibly pure so that, even though it is several miles long, light can still make it through. The glass must be so transparent that a window several miles thick still looks clear. The glass is drawn into a very thin strand, with a thickness comparable to that of a human hair. The glass strand is then coated in two layers of plastic. By coating the glass in plastic, you get the equivalent of a mirror around the glass strand. This mirror creates total internal reflection, just like a perfect mirror coating on the inside of a tube. Light traveling through the fiber bounces at shallow angles and stays completely within the fiber.
Fiber optic cameras are used for surveillance because they are small and lightweight. They are also tiny enough to be used in medicine, where doctors can visualize passages in the body without the need for surgery.
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