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| Basic Concepts | Reflection and Refraction | Lenses | Fiber Optics |
| How Optical Fibers Work, Part 1 | How Optical Fibers Work, Part 2 | How Optical Fibers Work, Part 3 |
| How Optical Fibers Work, Part 4 | How Optical Fibers Work, Part 5 | How Optical Fibers Work, Part 6 |

How Optical Fibers Work, Part 1

Fiber optics is one of the newer buzzwords these days. Optical fiber has a number of advantages over the copper wire used to make connections electrically. For example, optical fiber, being made of glass (or sometimes plastic), is immune to electromagnetic interference, such as is caused by thunderstorms. Also, because light has a much higher frequency than any radio signal we can generate, fiber has a wider bandwidth and can therefore carry more information at one time.

But just how does it work? We're talking about a thin, flexible "string" of glass. Looking sideways at it, we can see right through it. How can we keep light that's inside the fiber from getting out all along the length of the fiber?

A light ray striking water in a glass.

Consider an ordinary glass of water. We know that if we look through the water at an angle, images will appear distorted. This happens because light actually slows down a little bit when it enters the water, and speeds up again when it moves back into the air again.

Since the light has a slight but measurable width, if it hits the water at an angle, the part of the light that hits the water first will slow down first. The result is that the direction the light is traveling changes, and the path of the light actually bends at the surface of the water.

No matter what angle the light is traveling as it approaches the water, it will take a steeper angle once it actually enters the water. You can see this at any time by looking at a picture or newspaper through a glass of water, and by looking at different angles. Even a straw in a glass of water looks bent, although it really isn't. This phenomenon is called refraction.

Light refracting as it passes through a window pane.

The same phenomenon happens with glass, although we don't usually notice it when looking through a window. Nevertheless, light striking the glass at an angle bends as it slows down within the glass, and then bends again as it speeds up when leaving the glass. You can see this phenomenon clearly if you slide a piece of flat glass over the print in a book or newspaper.

Any substance that light can travel through will exhibit this phenomenon to some extent. Glass happens to be a very practical choice for optical fiber because it is reasonably strong, flexible, and has good light transmission characteristics.

The question to be answered now is, "How can we use this phenomenon to keep the light inside the glass, especially if we want to bend the glass (with the light still inside) around corners?" We will start looking at that on the next page.

Prev: Optics: Lenses Next: How Optical Fibers Work, Part 2

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