Optical fibers in communications

High-pnrity silica glass is nsed as the fiber material fiber diameters normally range between abont 5 and 100 p,m. The fibers are relatively flaw-free and, thns, remarkably 

Schematic diagram showing the components of an optical-fiber commnnications system. 

FigMie 21.19 Digital encoding scheme for optical communications. (a) A high-power pulse of photons corresponds to a 1 in the binary format, (b) A low-power photon pulse represents a 0. 

FigMre 21. 22 Graded-index optical-fiber design, (a) Fiber cross section, (b) Fiber radial index of refraction profile, (c) Input Ught pulse, (d) Internal reflection of a light ray. (e) Output light pulse. 

The optical behavior of a solid material is a function of its interactions with electromagnetic radiation having wavelengths within the visible region of the spectrum 

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Optical property refers to a material s response to exposure to electromagnetic radiation and, in particular, to visible light. This chapter first discusses some of the basic principles and concepts relating to the nature of electromagnetic radiation and its possible interactions with solid materials. Then it explores the optical behaviors of metallic and nonmetal-lic materials in terms of their absorption, reflection, and transmission characteristics. The final sections outline luminescence, photoconductivity, and light amplification by stimulated emission of radiation (laser), the practical use of these phenomena, and the use of optical fibers in communications. 

Le Kien, F. Liang, J. Q. Hakuta, K. Balykin, V. I., Field intensity distributions and polariza tion orientations in a vacuum clad subwavelength diameter optical fiber, Opt. Commun. 2004, 242,445 456... 

UL 1975 Standard for Fire Tests for Foamed Plastics Used for Decorative Purposes UL 2024 Standard for Optical-Fiber and Communications Cable Raceway UL 2043 Standard for Safety Fire Test for Heat and Visible Smoke Release for Discrete Products and Their Accessories Installed in Air-Handling Spaces... 

Problem International computer communications are often carried by optical fibers in cables laid along the ocean floor. If one strand of optical fiber weighs 1.19x10 Ib/m, what is the mass (in kg) of a cable made of six strands of optical fiber, each long enough to link New York and Paris (8.84X10 km) ... 

In most optical communication systems, the information is encoded onto a beam of light and transmitted through an optical fiber. In an ideal system, the information is undistorted by the transmission path. However, in a real optical fiber, the power level of the signal is decreased as it is transmitted, due to absorption and scattering losses in the fiber. As a result, the signal needs to be amplified or regenerated along the transmission path in order to be detected at the receiver side. Another detrimental effect... 

For some particular applications, glasses are also made by other technologies, for example by chemical vapor deposition to achieve extreme purity, as required in optical fibers for communication, or by roller chilling in the case of amorphous metals, which need extremely high quenching rates. The term amorphous is a more... 

Glogc D, Gardner WB (1979) in Chynoweth AG, Miller SE (eds) Optical Fiber Tde-communications. Chap. 6. Academic Press, New York... 

Bandwidth is one of the most important parameters of optical fibers, in addition to attenuation. Bandwidth determines the maximum transmission data rate or the maximum transmission distance. Most optical fiber communication systems adopt pulse modulation. If an input pulse waveform can be detected without distortion at the other end of the fiber, except for a decrease in the optical power, the maximum link length is limited by the fiber attenuation. However, in addition to the optical power attenuation, the output pulse will ako be generally broader in time than the input pulse. This pulse broadening restricts the transmission capacity, namely, the bandwidth of the fiber. The bandwidth is determined by the impulse response as follows [17] Optical fibers are usually considered quasi-linear systems, and therefore the output pulse is described by... 

In 1966 Kao and Hockham [1] described a new concept for a transmission medium. They suggested the possibility of information transmission by optical fiber. In 1970 scientists at Croning Inc. [2], fabricated silica optical fiber with a loss of 20 dB/km. This relatively low attenuation (at the time) suggested that optical communication could become a reality. A concentrated effort followed, and by the mid 1980s there were reports of low-loss silica fibers that were close to the theoretical limit. 

Fibers are very important objects in our life. Examples include natural silk spim by silkworms and spiders, synthetic fabrics such as nylon, polyesfer, or optical fibers for communication networks. Fibers can be drawn only from viscous fluids that harden during the pulling process. The hardening can be achieved either by cooling, such as in glass fibers or by loosing wafer, e.g.. 

Thesis, J., Brockmeyer, A., Groh, W., and Stehlin, T. E, Polymer optical fibers in data communications and sensor applications, in Polymers for Lightwave and Integrated Optics, Hornak, L. A., Ed., Marcel Dekker, New York, 1992, Chap. 2. 

Si02 is probably the most widely used ceramic material. Silica is an essential ingredient in glasses and many glass ceramics. Silica-based materials are used in thermal insulation, refractories, abrasives, fiber-reinforced composites, laboratory glassware, and so on. In the form of long continuous fibers, silica is used to make optical fibers for communication. Powders made using fine particles of silica are used in tires, paints, and many other applications. 

S. Shibata, T. Kitagawa, and M. Horiguchi, "WhoUy Synthesized Fluorine-Doped SUica Optical Fiber by the Sol-Gel Method," in Technica/Digest of the 13th European Conference on Optica/ Communication, He/sinki, Fin/and, Association of Electrical Engineers of Finland, Helsinki, 1987, pp. 147—150. 

The most important appHcation of fiber-optic laser-based communication is in long-distance telecommunications (92,93). Fiber-optic systems offer very high capacity, low cost-per-channel, light weight, small size, and immunity to crosstalk and electrical interference. 

In the early 1990s, there were more than 9 x 10 km of fiber-optical telecommunication links in practical use in the United States. In addition, many other countries, notably Canada, Japan, and western Europe, have installed extensive fiber-optic communication systems. There are several transoceanic fiber-based telephone cables. Fibers are in use for intracity telephone links, where bulky copper [7440-50-8] wine is replaced by thin optical fibers. This allows crowded conduits in large cities to carry more messages than if copper wine were used. Fiber optics are used for intercity long-haul telephone links, for interoffice tmnk lines, and have replaced many microwave communication links. 

However, optical fiber communications are not useful only for long-distance communication links. Fiber-optic data links are also used in a variety of short-distance systems, for example in computer—computer links and for internal communications on ships and aircraft. Figure 16 shows some possible appHcations for fiber-optic communications, with respect to length and bit rate. The common carrier appHcations, like telephone links. He to the upper right of the dashed line labeled 100 MHzkm. However, a wide variety of other lower performance appHcations, illustrated to the lower left of the dashed line, are in use or under development. 

Pigure 10 shows the typical commercial performance of LEDs used for optical data communication. Both free-space emission and fiber-coupled devices are shown, the latter exhibiting speeds of <10 ns. Typically there exists a tradeoff between speed and power in these devices, however performance has been plotted as a function of wavelength for purposes of clarity. In communication systems, photodetectors (qv) are employed as receivers rather than the human eye, making radiometric power emitted by the devices, or coupled into an optical fiber, an important figure of merit. 

Lithium Niobate. Lithium niobate [12031 -64-9], LiNbO, is normally formed by reaction of lithium hydroxide and niobium oxide. The salt has important uses in switches for optical fiber communication systems and is the material of choice in many electrooptic appHcations including waveguide modulators and sound acoustic wave devices. Crystals of lithium niobate ate usually grown by the Czochralski method foUowed by infiltration of wafers by metal vapor to adjust the index of refraction. 

Within your lifetime, extraordinary changes will sweep through modern technology. Classes and ceramics are two of the advanced materials that will make these changes possible. Optical fibers—which are already playing a major role in communication—will control our computers, and our automobiles will be much lighter and more economical. 

Light wave technologies provide a number of special challenges for polymeric materials. Polymer fibers offer the best potential for optical communications in local area network (LAN) applications, because their large core size makes it relatively cheap to attach connectors to them. There is a need for polymer fibers that have low losses and that can transmit the bandwidths needed for LAN applications the aciylate and methacrylate polymers now under study have poor loss and bandwidth performance. Research on monomer purification, polymerization to precise molecular-size distributions, and weU-controlled drawing processes is relevant here. There is also a need for precision plastic molding processes for mass prodnction of optical fiber connectors and splice hardware. A tenfold reduction in the cost of fiber and related devices is necessaiy to make the utilization of optical fiber and related devices economical for local area networks and tlie telecommunications loop. 

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