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“Listening” with Light
One morning, a car drove slowly on a side road in Texas. Thousands of kilometers away, a computer screen in England filled with a series of red lines, similar to the jagged lines of a seismograph’s readings. The red lines represented ground vibrations made by the sound of the car moving over the surface.
The vibrations caused by the car in Texas were sent to the computer in England by light signals sent through specially designed tubes called fiber optic cables.
Fiber Optics Transmit Light
Fiber optics, also called optical fibers, are long strands of pure glass that are as thin as a human hair. They are grouped in bundles called fiber optical cables that transmit light signals from one place to another. To transmit means to pass on.
Fiber optic cables work because of how light interacts with different kinds of matter. All light is a form of kinetic energy that travels through space and matter. Light is complex, and there is still much that scientists don’t know about it. There are different models of light that scientists use to better understand how light moves and how it interacts with matter. One model describes how light moves in straight-line paths called light rays. Whenever you see a narrow beam of light, it is actually a bundle of many parallel light rays.
Fiber Optics Communication
Fiber optic cables are commonly used to transmit information in communication systems. A communication system is a group of interacting components that function together to transmit or exchange information between people and equipment.
In a fiber-optic communication system, information is sent digitally through the cables. This means the information is translated into a numerical value, most often ones and zeroes.
Different patterns of light wave pulses represent different combinations of ones and zeroes Digital technology is different from analog technology because in analog technology, the information is recorded or used in its original form. A transmitter at one end of the fiber-optic cable sends the information digitally. A receiver on the other end picks up the information. The digital information is translated back into its original form, such as sound or light. Fiber optic cables are commonly used in telephone communications.
Think back to the computer screen in England filled with a series of red lines when the truck moved over the ground in Texas. That computer screen was a receiver in a communications system that used a fiber-optic cable. Pulses of laser light were sent through the cable. When the ground vibrated, it caused extremely small vibrations in the cable. These vibrations caused small changes in how the light moved through the cable. The company that owns the computer screen has designed special signal-processing techniques to analyze what the sounds are likely to be, such as a truck, a person walking, or the wind.
Analog vs. Digital Communications
Digital signals are more reliable than analog. This is because the recording does not become less precise over time. As long as the numbers can be read, you will always get exactly the same wave. Because of this, fiber optic communication systems most commonly use digital signals.
Think about someone speaking into a telephone. Their voice produces an analog signal in the form of a sound wave. That sound wave enters the telephone, where it is converted to digital pulses of light. This signal is made up of pulses of ones and zeros. These pulses then move through the optical fiber to the receiver, where they are changed back into an analog signal in the form of sound waves that the person at the other end can hear.
As the signal travels, it picks up a lot of noise. This is called interference. However, because the sound wave was broken down into discrete numbers, the converter can easily convert the sound wave back to the same pattern as the original signal.
In contrast, if the system used just analog signals, it would be difficult to separate out the interference because there are many possible frequencies and amplitudes the wave could have. The end result is a representation of the original signal. This can result in information being lost or garbled when it comes through. Digital calls are also more secure because the digital code encrypts the conversation so outside listeners cannot follow what is being said.
Kinds of Communication Systems
There are many kinds of communication systems that transmit information. When you use GPS on your phone, you are using a communication system that transmits information about your location through a kind of light wave called a microwave. When you listen to the radio, you are using a communication system that transmits sounds through radio waves.
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