Communication: How Fiber Optics Work

Fiber optics work on the principle of bending light, and they can replace bulkier and costlier metal wires in phone systems.

Before learning how fiber optics actually work, it may be useful to examine the system they often replace. From the earliest days of the telephone, phone companies have relied on electricity as the primary carrier between individual telephones. Electricity is an effective medium because its intensity can be readily adjusted and it can also be turned on or off. But electricity does have some shortcomings when it comes to long distance communications. Electrical lines generate heat, which means large telephone lines must be insulated and kept out of the reach of the general population. Individual copper wires can only carry one conversation at a time, which means a collection of these wires, called a trunk line, can become extremely large and barely manageable. Standard telephone lines require constant attention in order to maintain reliability.

The problem which faced telephone engineers was finding an alternative method of transmitting electronic signals that would require less space and less maintenance. Most materials failed the test because they could not carry signals without substantial losses or they were too fragile to withstand the rigors of telephone service. Engineers and scientist did discover that light was capable of transmitting information over a distance and could be manipulated to send digital signals, but the problem was finding a way to keep the light from escaping its container.

A flashlight is a perfect example of the benefits and limitations of light. Once the light is generated by the bulb, it tends to spread out in all directions. Lenses and reflectors can help focus light in a more specific direction, but eventually the light waves will scatter so far apart that the illumination benefit is lost. The only solution is to build a larger flashlight, something approaching a theatrical spotlight. Again, the light may appear focused at a short distance, but it will eventually dissipate. If light were to be used for communication, it must be forced to remain in a closed environment and also be able to bend without losing information.



A simple scientific experiment involving a stream of water eventually proved that light could indeed be bent. When water streams out of a small opening, it forms a natural arc. If a light source is placed behind the source of the stream, the light waves will bounce through and around the 'walls' of the flowing water. But if the diameter of the stream is adjusted properly, the light waves bounce into the walls at a certain angle. Instead of penetrating the walls and continuing outwards, the light wave bounces off at an angle and essentially ping-pongs against the opposite wall. The light waves are constantly bouncing off the walls and cannot escape the water. Once the stream begins to bend in its natural arc, the light is forced to bend with it. This containment of light is the principle behind fiber optics.

Since water would not be suitable for use in a telecommunication system, engineers eventually decided that another liquid, pure glass, would also be able to carry light without significant signal loss. The main problem was creating enough glass fibers to be useful. Early fiber optic fibers were created by taking purified molten glass to the top of a tall laboratory and allowing the glass to literally drip to the floor.

The very thin ropes of pure glass would allow light to travel from one end to the other without escaping into the outside air. Eventually scientists would develop ways to produce these fibers commercially and the fiber optics industry was born.

Fiber optic lines use light in the same way that earlier copper wires used electricity. A human voice on one end of the phone system speaks into a miniature microphone. The soundwaves are then converted into pulses of light. These pulses travel along the fiber of glass (or other clear polymer) until they reach a receiver. The light pulses are then translated back into recognizable soundwaves through a digital process. Most communication is conducted through a mix of copper wires, fiber optics and microwave transmitters, but fiber optics have replaced a great deal of the bulky copper trunk lines which connect city telephone systems to others.

The benefits of fiber optics in communication systems are size and capacity. A single fiber optic bundle can replace a traditional wire trunk line measuring ten feet in diameter. The signals sent through a fiber optic network are often digital, which allows both humans and computers to use the same lines. Older phone systems used analog technology, which is suitable for human conversation which exists in waves, but not for computers which deal in binary (on/off) coding. Light waves can carry human conversation at the same time they deliver binary code for computers. The only drawback to fiber optics appears to be their relative fragility. Damage caused to a fiber optic network by an errant shovel or natural disaster can take longer to repair. Producing usable fiber optic lines also requires some very stringent and costly manufacturing methods. Quite often the fiber optics used for decorative art projects are created from cheaper forms of plastic which don't require as much purity.

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