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What is Optical Fiber? - Definition & Concept

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  • 0:00 Optical Fiber Defined
  • 2:00 Types of Optical Fiber
  • 2:33 Advantages & Limitations
  • 3:05 Lesson Summary
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Lesson Transcript
Instructor: David Whitsett

David has taught computer applications, computer fundamentals, computer networking, and marketing at the college level. He has a MBA in marketing.

Optical fiber is a type of cabling technology that uses light to carry voice and data communications (telecommunications) over distances both great and small. This lesson will provide a definition of optical fiber, explore the different types and explain how the different types are used. We'll also look at the advantages of optical fiber over traditional copper wiring and examine the limitations.

Optical Fiber Defined

An optical fiber is a very thin strand of plastic or glass that is used to transmit messages via light. These strands are bundled together in a protective sheath or cover and the whole assembly (the optical fibers and other parts inside the sheath) is often referred to as fiber optic cable or just fiber.

Think of two people standing at opposite ends of a long dark hallway and signaling each other with flashlights. In the case of optical fiber, the strand (the hallway in the example) can be about as thin as a human hair, and the material it is made of (glass or plastic) is very pure. So the messages transmitted via light can travel a very long way, across oceans.

But, you ask, don't fiber optic cables bend? How does a signal of light, which travels in a straight line (remember the flashlight beam), go around a curve? The answer is in the way a fiber optic cable is built. Wrapped around each strand of optical fiber is cladding, an outer optical material that reflects the light back into the core strand. Think of using a mirror to reflect a beam of light around a corner. Cladding acts as a mirror all along the cable, continuously reflecting light along the cable down the intended path.

The transmitters at either end of an optical fiber cable typically use light-emitting diodes (LEDs) or laser diodes to generate the light. Think of our flashlight example, where the flashlight is the light source. Optical receivers take the light signal from the cable and convert it into an electrical signal. The data moves at a very high rate of speed; think of milliseconds for a message to go across the Atlantic! Why? Light travels faster than an electrical signal through a copper cable.

Fiber attenuation (signal loss) and distortion are dealt with over long runs with the use of fiber optic amplifiers or repeaters. These devices boost the signal at a midpoint and send it back along its way.

Types of Optical Fiber

The two main types of fiber used in telecommunications are single-mode fiber and multi-mode fiber. In general, multi-mode fiber is larger in diameter, is less expensive and used for shorter distance runs, like as a patch cable or for runs within an office building from floor-to-floor to connect network users. Single-mode fiber is used for longer, high-bandwidth (greater performance capacity) runs, like from city-to-city. You'll often see workers alongside a new road or near a new office park installing fiber optic cable from large spools.

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