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Introduction to Fiber Optics

How it works:

A glass tunnel through which the light travels is created. When the light hits the cladding, it interacts with and reflects back into the core. Because of this design, the light can “bend” around curves in the fiber and makes it possible to travel further distances without having to be repeated.

Animated Fiber

The light that travels along the fiber is made up of a binary code that pulses “on” and “off” and determines what information a given signal contains. The advantage of fiber is that these on/off pulses can be: translated video, computer, or voice data depending on the type of transmitter and receiver used.

Facts About Fiber Optics

Fiber optics were needed because television cables were becoming more capable of carrying more information than copper wire so computer and telephone companies needed something to compete.

Currently all new undersea cables are made of optical fibers.

Experts say that sometime in the early 21st century, 98% of copper wire will be replaced by fiber optic cable.

Fiber optic cable installed for copper wire that already needs replacing is less expensive since it only needs repeaters to amplify the signals running through it every six miles rather than every mile.

Fiber Repeaters

Optical fiber phone lines cannot be bugged or tapped.

A fiber is thinner than a human hair.

Advantages of Fiber Optic Cables Over Copper

Speed: Fiber optic networks operate at speeds up to 10 gigabits per second or higher, as opposed to 1.54 megabits per second for copper. A fiber optic system is now capable of transmitting the equivalent of an entire encyclopedia (24 volumes) of information in one second. Fiber can carry information so fast that you could transmit three television episodes in one second.

Bandwidth: Taken in bulk, it would take 33 tons of copper to transmit the same amount of information handled by 1/4 pound of optical fiber.

Resistance: Fiber optic cables have a greater resistance to electromagnetic noise such as radios, motors or other nearby cables. Because optical fibers carry beams of light, they are free of electrical noise and interference.

Capacity: Fiber optics have a greater capacity for information which means smaller cables can be used. An optical fiber cable the size of an electrical cord can replace a copper cable hundreds of times thicker.

Why Fiber Optics?

Fiber Optics

LAN's developed as a result to the information explosion that occurred in the late 1980's. The need for office, laboratory, and factory computers to share information became essential. Since the 1980's, many media have been developed for use in LAN's, each meeting a specific user demand. Glass fiber was developed for use in long distance, high bandwidth applications, but the high cost of hardware and installation has daunted users.

Twisted pair, on the other hand, was developed as a low cost alternative medium for use in shorter distance applications. Twisted pair seemed to be an ideal medium for LAN's, but as computer graphics have become more "graphic intensive", LAN's have been required to transmit a much greater volume of information, requiring a media with a much higher bandwidth. Since twisted pair is not capable of supporting the higher signaling rates, there has been an increased interest in developing a low cost fiber solution.

Types of Optical Fibers & Cables

Fiber Optic Cable

The differences among fibers is their core sizes (the light-carrying region of the fiber). Multi-mode fiber has much larger core than Singlemode fiber. Multi-mode fibers have a combined diameter in the 50-1000 um range. (where um is a micron and one micron is 1/250th the width of a human hair). Each fiber in a Multi-mode cable is capable of carrying a different signal independent from those on the other fibers in the cable bundle. These larger core sizes generally have greater bandwidth and are easier to couple and interconnect. It allows hundreds of rays to light to propagate through the fiber simultaneously. Multi-mode fiber today is used primarily in premise applications, where transmission distances are less than two kilometers.

Singlemode fiber glass has a much smaller core that allows only one mode of light to propagate through the core. Singlemode fiber has a higher bandwidth and less loss than Multi-mode fiber and for this reason it is the ideal transmission medium for many applications. The standard Singlemode fiber core is approximately 8-10 um in diameter. Because of its greater information-carrying capacity, Singlemode fiber is typically used for longer distances and higher-bandwidth applications.

While is might appear that Multi-mode fibers have higher information carrying capacity, this is not the case. Singlemode fibers retain the integrity of each light pulse over longer distances which allows more information to be transmitted. This is why Multi-mode fibers are used for shorter distances.

Multimode and Single-Mode Fiber

POF-or Plastic Optical Fiber-is a newer plastic-based cable which promises performance similar to Singlemode Cable, but at a lower cost. POF is still in the infancy stage although many companies are noticing its potential.

An Application of Fiber Optics

Ok, you are probably wondering how fiber optics is used in every day life.


Take for example, your basic telephone conversation. In the fiber optic telecommunication system, a message is sent from one end through an electric cable to an encoder which transmits a signal through a glass fiber optic cable. It then travels through a repeater, back through the cable, into a decoder and through an electric cable into the phone line on the other end. The sound waves that your voice generates becomes wave of electricity in the mouthpiece of your telephone. Rather than electricity flowing through copper wire to your destination, fiber optics allows electricity to pass through the encoder which measures the waves of electricity 8000 times each second. The encoder then converts these waves into "on"/"off" pulses of infrared light that are digitized allowing them to be read by the telephone system. Receiving the digitized message is the decoder. This device converts the laser light back into electrical waves. These electrical waves are changed into the sound that we hear through the phone. This same process not only works for the telephone, but also other sources that transmit data (i.e. computers, televisions).