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| 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 2

Now, consider looking into a glass of water from below the surface of the water. If you look up through the bottom of the glass, you will see a somewhat distorted view of the ceiling or whatever is above the glass. However, if you look in from the side of the glass and observe the underside of the top surface, you will begin to note an interesting and useful effect.

If you are looking up from a steep angle, the light you see entered the top surface of the water at a shallower angle, as shown on the left. However. as you look at the underside of the top surface from a shallower angle, as shown on the right, you will find a point at which light can't enter the top surface at a yet shallower angle. At this point, the top surface of the water looks like a perfect mirror, even though you know it isn't.

Light refracting through the surface of water. Light reflecting from the underside of the water's surface.

Now, the light you see is reflected from the surface, rather than being refracted through it. This effect persists for all angles shallower than the critical angle at which the phenomenon first appears. As you might expect, the same phenomenon is exhibited by glass or any other material through which light might pass.


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