Fiber Optics: A Guide To Wave Guides
Light travels in straight lines, so it was remarkable that a British physicist named John Tyndall demonstrated in 1870 how light could be guided around a corner. Tyndall opened a spout on the side of a tank of water and shined a light through the pouring water. The water appeared to guide the light in a curve.
As early as 1880, Alexander Graham Bell patented a device named a "photophone," which used sunlight to transmit conversations without copper wire. Nightfall, cloudiness, and foul weather made sunlight undependable, but those early experiments did prove that light could transmit sound.
Another part of the problem of using light to transmit sound is that light gets dimmer the farther it travels. A series of mirrors and tubes could be used to reflect light and transmit human voices around corners, but where was there a light strong and reliable enough to travel over mountains, through foul weather, and over great distances?
Nearly eighty years after Bell's patent, researchers found ways of detecting and modulating newly inverted laser technology and thus, the powerful, reliable light source was found.
The problem of getting light to travel other than straight ahead in any medium was still there.
John Tyndall's pouring water experiment demonstrated a phenomenon known as Total Internal Reflection. When light traveling through a medium (such as water) hits the boundary of less-dense material (such as air) at a small angle, the light is reflected as if the boundary were a mirror.
Fiber optics uses this same principal of total internal reflection to "carry" light. Instead of using water, optical fibers use glass as the medium to carry the light, with a slightly less-dense glass around it to act as the air did in Tyndall's experiment.
(See: Laser Communication through Glass )