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Fiber Optics

Fiber Optics

Fiber optics is the set of technologies that enables the point-to-point transmission of signals in the form of lightinstead of in the form of electricity. The main component is optical fiber, the thread of glass-like material that carries the optical signal. Two related components are: (1) the light emitting diode (LED) and its advanced cousin, the semiconductor diode laser , which convert electrical signals to optical signals and couple them into the fiber; and (2) the photodiode, which receives optical signals from the fiber and converts them back to electrical signals.

Although fiber optics has many applications, including its use in sensors , its greatest impact has been in telecommunications. For millennia, humans used optical technology to send signals over distancefor example, as smoke puffs, reflected sunlight, or flares. Remember American Revolutionary War hero Paul Revere's ride and the warning signal: "one if by land and two if by sea?" But, these techniques are limited to what can be seen by human beings within a finite line of sight. Wired and wireless electrical technologies allow global, even interplanetary, transmission. But, these technologies have high attenuation , high noise susceptibility, and low bandwidth . While coaxial cable helps alleviate these problems, fiber optics provides a better point-to-point transmission medium than any form of wired electronics.

Description

An optical fiber's diameter is typically only one-eighth of a millimeter (0.005 inches), but one rarely sees a bare fiber. When it is covered by protective plastic, an individual fiber looks like an insulated wire. Or, many fibers are incorporated into a cable that includes an internal plastic spine, for strength and rigidity, and a hard outer jacket that protects the fibers from external damage (including bites from gophers or sharks). Like wires or coaxial cable (co-ax), fibers can be quite long but, unlike wires or co-ax, an 80-kilometer (50-mile) fiber span may not need an intermediate repeater.

Optical fiber is not uniform in its cross-section. A concentric cylindrical region, called the "core," lies inside the fiber. The core has a slightly different chemistry from the fiber's outer layer, called the "cladding." Light, launched into the fiber's core, travels the length of the fiber, staying inside the core by ricocheting off its walls.

Operation

When an electrical signal moves along a wire, individual electrons move slowly, shifting from atom to atom. But, optical signals are carried by photons, which are launched into the fiber and carry the signal as they traverse the fiber. Electrical signals move along a wire or co-ax at a bandwidth-dependent rate, typically around 20 percent of the speed of light. While optical signals, and electrical signals in free space, move at the speed of light, light moves slower in glass than in air. So, optical signals traverse fiber at about two-thirds the speed of light, which is still three times as fast as electrical signals move along wires.

In multi-mode fiber, different ricochet angles (called "modes") have different velocities so, a narrow optical pulse spreads as it moves. In more expensive single-mode fiber, the smaller core diameter (eight microns or 0.0003 inches, instead of 62.5 microns or 0.0025 inches) supports only one mode, which eliminates this modal distortion and allows pulses to be more closely spaced, giving a higher data-rate. Since different wavelengths have slightly different velocities, even single-mode pulses can spread. Using a light source with a narrow range of wavelength reduces this consequence, known as chromatic dispersion , which allows pulses to be even more closely spaced, resulting in an even higher data-rate. Many commercial long-distance optical fibers carry 2.5 gigabits per second (Gbps) today, and new transmitters and receivers support ten Gbpsover the same fiber.

Techniques

Since a digitized voice signal requires 64 kilobits per second (Kbps), a single fiber at 2.5 Gbps carries more than 30,000 voice channels. A process called "time-division multiplexing" interleaves the individual signals. Another technology, called "wavelength division multiplexing" (WDM), has recently become practical. WDM allows several channels, each at 2.5 Gbps, to use the same fiber by using different wavelengths. These wavelengths must be far enough apart to be practically separable at the receiver, but close enough together to reside within a fiber's low-attenuation wavelength windows.

Fiber optics is highly nonlinear . When analog signals (like conventional television channels) are transmitted over fiber, the fiber can not be pushed to its limits. So, state-of-the-art transmission is digital, because digital signals are not as affected by nonlinearities. One such nonlinearity, which causes light to move faster through a lit fiber than through a dark fiber, imposes practical limits on the number of WDM channels on a single fiber. Data rate and WDM are both being intensely researched.

Characteristics

The maximum span of any transmission link is determined by the signal-to-noise ratio (SNR) at the receiver. Increasing a wire's length increases both the received noise power and the signal's attenuation. So, wire's SNR is a strong inverse function of length. The property that keeps an optical signal inside a fiber's core also keeps external interference outside it. Since fiber's received noise power is practically independent of length, fiber's SNR depends on attenuation only, making it a relatively weak function of length. So, fiber spans can be longer than wire spans.

Different wavelengths not only have different velocities, but they also suffer different attenuation. The practical attenuation needed in a short span of optical fiber requires the light source's wavelength to be in the infrared range of 0.7 to 1.6 microns. Fortunately, cheap LEDs operate at 0.8 microns. The very low attenuation needed in a long span occurs over two narrow regions of wavelength: around 1.3 and 1.5 microns, where light sources are expensive. The lowest attenuation occurs at 1.5 microns, but chromatic dispersion is minimized at 1.3 microns. Not surprisingly, long-distance optical transmission occurs around these two wavelengths.

Although low attenuation and low noise immunity are important, fiber's most important characteristic is its huge bandwidth. Comparing information transmission to water flow, bandwidth corresponds to pipe diameter. On a scale where a telephone channel (4 kHz) corresponds to 1-centimeter (3/8-inch) copper tubing, a co-ax carrying 70 television channels (350 MHz) corresponds to a 2 meter (6-foot) sewer pipe. Fiber's long-span attenuation requirement allows about 15 THz (terahertz) in each of the 1.3- and 1.5-micron windows. This 30 THz of ultimate capacity corresponds to a pipe with 1.6-kilometer (one-mile) diameter. Researchers have only begun to figure out how to use it all.

Cost

Carrying 100 Mbps (megabits per second) over a short span, where multi-mode fiber and LEDs are used, fiber optics costs only a little more than wired electronics. For high rates over long spans, where single-mode fiber and semiconductor diode lasers must be used, fiber optics is expensive. But, the huge bandwidth makes it cost-effective. While fiber's material (silica) is cheaper than wire's (copper), fiber is more expensive to manufacture especially single-mode fiber. However, since new installation cost is typically

  Access infrastructure Backbone network
Broadcast application I II
Point-to-point apps III IV

much higher than the cost of what is being installed, it is common practice to include dark fiber in any wire installation, even if there are no current plans for it.

There are other cost issues, as well. Fiber optics is more difficult to use than wire, and technicians need to be trained. While wire can be soldered or wrapped around a terminal, optical fiber must be carefully spliced. Fiber connectors, especially for single-mode fiber, are more expensive than wire connectors.

Application

Consider Table 1. Users get access (left column) to information signals by several competing media. People access (I) commercial broadcast television signals by local antenna, co-ax, or direct dish, and (II) point-to-point applications, like telephony or connecting to an Internet service provider, by wire or local wireless (cellular). But, the backbone infrastructures (right column), which distribute these signals over wide areas, use an application-dependent medium-of-choice. Commercial television is effectively (III) broadcast using geo-synchronous satellites, and the wide-area networks for point-to-point applications, like long-distance networks for telephony and the Internet for data, typically use fiber optics.

This may all change, of course, as the technology, the industry, the applications, and the economics evolve. Although technically feasible, fiber-to-the-home and fiber-to-the-desktop are economically difficult to justify. If video-conferencing becomes popular, perhaps it will be the so-called "golden service" that makes it happen.

Future

Because of the nonlinearity that causes light to go faster through a lit fiber than a dark fiber, the photons at the back of a pulse can actually catch up to the photons at the front. A soliton is a pulse whose shape is retained because this effect carefully balances the effects that widen pulsesand researchers are trying to make them practical. With all that unused potential bandwidth, fiber optics is the logical technology for making networks that must scale easily, like the Internet. If research efforts in photonic switching and optical computing are fruitful, there will be wonderful synergies with fiber optic transmission. If researchers learn to master solitons and these other research efforts are fruitful, fiber optics has a "bright" future.

see also Digital Logic Design; Networks; Telecommunications; Transmission Media.

Richard A. Thompson

Bibliography

Green, Paul E. Fiber Optic Networks. Upper Saddle River, NJ: Prentice Hall, 1993.

Palais, Joseph C. Fiber Optic Communications, 4th ed. Upper Saddle River, NJ: Prentice Hall, 1998.

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"Fiber Optics." Computer Sciences. . Encyclopedia.com. (October 22, 2017). http://www.encyclopedia.com/computing/news-wires-white-papers-and-books/fiber-optics

"Fiber Optics." Computer Sciences. . Retrieved October 22, 2017 from Encyclopedia.com: http://www.encyclopedia.com/computing/news-wires-white-papers-and-books/fiber-optics

Fiber Optics

FIBER OPTICS

Fiber optics is the transmission of data via light waves passed through glass threads. Most major telephone companies have replaced, or are in the process of replacing, traditional copper telephone lines with fiber optic cables. Additionally, local-area networks often use fiber optic technology. Single-mode fiber is used in conjunction with laser light to transfer data more than five miles in distance. Multi-mode fiber is used with a lower frequency light-emitting diode (LED) for shorter transmissions.

Fiber optic cables can carry significantly more data at a much greater speed than metal cables. For this reason, companies across the globe became interested in the technology, starting as early as the 1970s. For example, several Japanese companies, including Furukawa Electric Company Ltd., worked cooperatively to develop fiber optic cables capable of transmitting more information faster and more reliably than conventional microwave cable. Furukawa's developments throughout the 1980s included the first single-mode fiber optic connector using high-heat fusion splicing methods; a stronger, more heat resistant fiber optic cable; and a flexible fiber optic scope for use in examining the inside of pipes.

Western Electric engineers started experimenting with fiber optics in 1979. In 1980, AT&T Corp. sought permission from the U.S. Federal Communications Commission to build a 611-mile fiber optic network connecting major cities in the Northeastern United States. By 1984, fiber cables in the United States had reached 250,000 miles. Other leading telecommunications players, such as Nippon Telegraph and Telephone Corp., also began to focus on fiber optic technologies in the early 1980s. To bolster its fiber optic efforts, MCI Communications Corp. bought 100,000 kilometers of fiber optic cable from Corning Inc., which invested $87 million on new fiber optic plant facilities in 1986. At roughly the same time, the Williams Companies created Williams Telecommunications, a telecommunications unit which developed a fiber optic cable network that could be run inside unused steel pipelines; AMP Inc. spent more than $100 million in the development of fiber optics technology; and NYNEX Corp. entered the international long distance business by forming a $400 million joint venture to lay a transatlantic fiber optic cable. In 1988, GTE Laboratories developed the first fiber optic amplifier, and Bell Laboratories sent light pulses over fiber optic cables for 2,480 miles, setting a distance record. That year, the first transatlantic fiber optic cable was completed. In 1989, AT&T and Kokusai Denshin Denwa brought the first transpacific fiber optic cable into use.

Advances in fiber optics continued into the next decade as an increasing number of telecommunications companies, as well as firms in other industries, began embracing the technology. MCI Communications Corp. and British Telecom began working together to lay a transatlantic fiber optic cable in 1990. Cable company Cox Enterprises Inc. acquired a 50-percent stake in fiber optics vendor Teleport Communications Group. In 1992, Nynex Corp. revealed its intent to lay a fiber optic cable connecting the eastern United States with Japan via England and the Middle East. LDDS Communications, the predecessor to WorldCom, gained access to its first nationwide fiber optic network in 1995 when it paid $2.5 billion for WilTel Network Services, a unit of the Williams Companies. Chevron Corp. pioneered the use of fiber optic cables to monitor oil field production in 1996. Simplex Technologies Inc. partnered with Tyco into 1997 to form Tyco Submarine Systems Ltd., an undersea fiber optic telecommunication cable system. The following year, ADC Telecommunications Inc. introduced the EtherRing switch, which allowed less expensive implementation of Ethernet technology over fiber optic networks. Furukawa began developing and marketing fiber optic products in North America in 1999 via its FITEL Technologies Inc. subsidiary.

Fiber optic developments continued to improve telecommunications in 2000 and 2001. To improve the speed and quality of their networks, many organizations began upgrading to optical Ethernet systems. Nortel Networks, for example, started converting its North American ATM systems to optical Ethernet networks. Canadian financial giant CICB also began using optical Ethernet networking in Toronto. According to an October 2001 article in Business Communications Review, "the rationale for these activities is straightforward: simpler, faster and more reliable networking opportunities for rethinking server and storage distribution, and increased knowledge-worker productivity. The reason these are taking place now is the maturing of Ethernet transmission and switching, and the increased investment in metropolitan optical networking." Many industry analysts believe that all communications eventually will use fiber optic technology in one form or another.

FURTHER READING:

"About Fiber Optics." Port Huron, MI: AboutFiberOptics.com, 2001. Available from www.aboutfiberoptics.com.

"Fiber Optics." In Webopedia. Darien, CT: Internet.com, 2001. Available from e-comm.webopedia.com.

"Fiber Optics to the Fore." Washington, DC: National Academy of Sciences, 2001. Available from www4.nas.edu.

Rybczynski, Tony. "Optical EthernetPreparing for the Transition." Business Communications Review. October 2001.

SEE ALSO: AT&T Corp.; Bandwidth; Connectivity, Internet; Internet Infrastructure; Photonics

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"Fiber Optics." Gale Encyclopedia of E-Commerce. . Encyclopedia.com. 22 Oct. 2017 <http://www.encyclopedia.com>.

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Fiber Optics

FIBER OPTICS

FIBER OPTICS. Narinder Kapany did not believe a high school teacher who told him that light could only travel in a straight line. His fascination with the idea set off a lifetime of research into fiber optics, which involves the use of reflection to transmit light through fibers of glass or plastic. In 1954, Kapany reported in the British journal Nature that he had successfully transmitted images through fiber optic bundles of transparent glass or plastic rods. Kapany's research built on more than 200 years of research and investigation into sending communications over translucent devices.

The American inventor Alexander Graham Bell dreamed of sending communications signals through the air via light impulses. He patented an optical telephone system in 1880, called the Photophone, but his invention of the landline telephone was more practical, thus receiving the lion's share of his time and effort. Further innovation in fiber optics was uneven until the 1920s when Clarence W. Hansell of the United States and John Logie Baird in England patented the idea of using hollow rods to transmit images for television systems. Despite the patent, the first person that established image transmission through a bundle of optical fibers was Heinrich Lamm, a medical student in Germany, who later moved to the United States to avoid persecution by the Nazis.

In 1955, after receiving a doctorate, Kapany journeyed to the United States to teach at the University of Rochester, in New York. In 1960, he moved to California's Silicon Valley and founded Optics Technology, taking it public in 1967. Another Northern California team, this one based at Stanford University, also worked on fiber optic research. Antoni E. Karbowiak and Charles K. Kao led a team examining the properties of fiber and concluded that impurities led to loss of transmission. The team attempted to figure out why light dimmed only a few yards down fiber optic strands, called "fiber attenuation." In 1966, after Karbowiak left Stanford, Kao developed a proposal for long-distance fiber optic communications over single-mode fibers. Although skeptics doubted Kao's research, he proved that fiber could be used for communications systems.

In the 1960s, Kao continued his theoretical and practical research, receiving twenty-nine patents for ideas on manufacturing pure glass fibers to splicing fibers to form communications lines. For their important early work, many observers have dubbed either Kapany or Kao as "the father of fiber optics."

Corning Glass Works produced the first commercial fiber optic cable in 1970. Company scientists used fused silica, an extremely pure material with a high melting point, to perfect fiber optic cable. Less than a decade later, in 1978, communications giant AT&T demonstrated the first fiber communications system. From this humble beginning, several million miles of fiber have been installed around the world, both on land and undersea.

In the early 1980s, when deregulation opened the telecommunications industry, telephony carriers built the national backbone of the industry on fiber optics. Soon, the technology spread from long-distance to other applications, ultimately setting the stage for nationwide fiber systems and the Internet.

In the mid-to late-1990s, the growth of the Internet and a "New Economy" based online solidified the idea that future communications networks would be built on fiber optics, or "broadband" technology. At the height of dot-com mania, companies rushed to connect Internet users to vast broadband networks, which offered the kind of high-speed access needed to fuel the growth of the wired economy.

After the dot-com economic bubble burst, however, the fiber optics industry virtually collapsed. Many formerly solid companies, such as Lucent and Nortel, foundered and startup money for new companies vanished. The fiber optic industry successfully increased bandwidth around the world, but was spread too thin in an effort to build new systems. When an economic recession hit the United States in the early 2000s, many companies were extended beyond their means.

Fiber optic data transmissions carried over silica fiber is at the heart of worldwide communications. The high bandwidth, light-carrying medium transports voice, video, and data and is the keystone of the Internet. Since the 1980s, communications companies have placed more than 300 million miles of fiber optic cable in the ground. However, less than 10 percent of this wiring is being used, eliminating any hope for profitability among many companies. These companies overextended their credit limits to install the fiber optic lines, but could not get enough users "lit" to justify the expense.

BIBLIOGRAPHY

Hecht, Jeff. City of Light: The Story of Fiber Optics. New York: Oxford University Press, 1999.

Hitz, Breck, James J. Ewing, and Jeff Hecht. Introduction to Laser Technology. 3d ed. New York: Wiley-IEEE Press, 2001.

Palais, Joseph C. Fiber Optic Communications. 4th ed. Garden City, N.J.: Prentice-Hall, 1998.

BobBatchelor

See alsoComputers and Computer Industry ; Telecommunications .

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Fiber Optics

Fiber optics

Optical fiber is a very thin strand of glass or plastic capable of transmitting light from one point to another. Since the late 1950s, optical fibers have emerged as revolutionary tools in the fields of medicine and telecommunications. These fibers can transmit light pulses containing data up to 13,000 miles (20,900 kilometers), and do so without significant distortion. The fibers also permit the "piping" of light into the body, allowing doctors to see and diagnose conditions without the use of surgery. Optical fibers operate by continuously reflecting light (and images) down the length of the glass core.

Production of optical fibers

Optical fibers are manufactured in a multistep process: the inner wall of a silica glass tube is coated with 100 or more successive thin layers of purer glass. The tube is then heated to 3,632°F (2,000°C) and stretched into a strand of thin, flexible fiber. The result is a clad fiber, approximately 0.0005 inch (0.0013 centimeter) in diameter. By comparison, a human hair measures 0.002 inch (0.005 centimeter).

The use of fiber optics

Optical fibers were first used in medicine in the late 1950s when fiber optic bundles were added to endoscopes (optical instruments used to examine the inside of hollow organs or tubes in the body). The new endoscope, called a fiberscope, consisted of two bundles of fibers. One bundle carried light down to the area to be studied, while the other carried a color image of the area back to the physician. Because of its small size and flexibility, the fiberscope can view many areas inside the body, such as veins, arteries, the digestive system, and the heart.

The field of telecommunications first used optical fibers in 1966. Today a telephone conversation can be carried over optical fibers by a method called digital transmission. In this method, sound waves are converted into electrical signals, each of which is then assigned a digital code of 1 or 0. The light carries the digitally encoded information by emitting a series of pulses: a 1 would be represented by a light pulse, while a 0 would be represented by the absence of a pulse. At the receiving end, the process is reversed: light pulses are converted back into electronic data, which are then converted back into sound waves.

By using digital transmission, telecommunications systems carry more information farther over a smaller cable system than its copper wire predecessor. A typical copper bundle measuring 3 inches (7.6 centimeters) in diameter can be replaced by a 0.25-inch (0.64-centimeter) wide optical fiber carrying the same amount of data. This improvement becomes

important where telephone cables must be placed underground in limited space.

The tiny size of optical fibers also brings about a significant reduction in the weight of a particular system. Replacing copper aircraft instrument wiring can save up to 1,000 pounds (454 kilograms), allowing for more economical fuel consumption. Optical fibers are also immune to electromagnetic interference, making them roughly 100 times more accurate than copper. They typically allow only 1 error in 100 million bits of data transmitted.

Optical fibers and television

Optical fibers have proven to be an ideal method of transmitting high-definition television (HDTV) signals. Because its transmission contains twice as much information as those of conventional television, HDTV features much greater clarity and definition in its picture. However, standard television technology cannot transmit so much information at once. Using optical fibers, the HDTV signal can be transmitted as a digital light-pulse, providing a near-flawless image. HDTV reproduction is far superior to broadcast transmission, just as music from a digital compact disc is superior to that broadcast over FM radio.

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fiber optics

fiber optics A means of transmitting analog or digital information using light signals over an optical fiber. An optical fiber is a thin transparent filament made either of glass or, for short distances, special plastics; the diameter of the fiber ranges downward from 125 micrometers, with a number of preferred sizes now being adopted as standard. The information is carried as a light signal, typically in the infrared with a wavelength of about 1200 to 1550 nanometers, and generated by an electrical-to-optical transducer, usually a switchable semiconductor laser. Light of wavelength 1200 nm has a frequency of 250 000 gigahertz (GHz), and is in principle capable of transmitting at bit rates of the order of 100 000 Gbps. The highest bit rates achieved in the laboratory are of the order of 1000 Gbps, and the highest rates in normal use are of the order of a few hundred Mbps, the limits being set by the speeds at which the semiconductor lasers and the optical-to-electrical transducers can operate.

A variety of methods are used to reduce the loss of the optical signal and hence increase signaling distance. The material of which the fiber is made is very pure, and by varying the refractive index of the material across the fiber it is possible to cause light rays at less than a certain angle to the axis of the fiber to be totally internally reflected back into the fiber. This reflection may take place at a discrete boundary between glasses of different refractive index (stepped index fiber), or may take place in a region of gradually varying refractive index (graded index fiber). If the fiber is made very thin, with a diameter of the order of the wavelength of the light, the light rays can only propagate along the fiber (monomode fiber). On a very long path, it is necessary to install amplifiers to regenerate the signal – by converting it from an optical to an electrical form, amplifying the electrical signal, and then reconverting it to an optical signal. Some amplifier designs exploit the nonlinear optical properties of certain glasses to allow direct amplification of the optical signal using a locally powered second laser as the power source.

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fiber optics

fiber optics, transmission of digitized messages or information by light pulses along hair-thin glass or plastic fibers. Each fiber is surrounded by a cladding having a high index of refractance so that the light is internally reflected and travels the length of the fiber without escaping. Cables of optical fibers can be made smaller and lighter than cables using copper wires or coaxial tubes, yet they can carry much more information, making them useful for transmitting large amounts of data between computers and for carrying data-intensive television pictures or many simultaneous phone conversations. Optical fibers are immune to electromagnetic interference (from lightning, nearby electric motors, and similar sources) and to crosstalk from adjoining wires, and tapping into them is more easily detected. To keep a signal from deteriorating, optical fibers require fewer repeaters over a given distance than does copper wire. In addition to communications, optical fibers are used in medical procedures, automobiles, aircraft and many other applications. In 2009 Charles K. Kao was awarded the Nobel Prize in physics for determining that purer glass was what was needed to create optical fibers that could transmit light over longer distances than the 20 meters that was possible in 1966. His insight led to the Corning Glass Works' development in 1970 of long, ultrapure glass fibers.

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fiber optics

fi·ber op·tics • pl. n. [treated as sing.] the use of thin flexible fibers of glass or other transparent solids to transmit light signals, chiefly for telecommunications or for internal examination of the body. ∎  [treated as pl.] the fibers and associated devices so used. DERIVATIVES: fi·ber-op·tic adj.

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