Practical Industrial Data Networks:Design, Installation and ...

Fiber optics overview 75N 1N 2N 1N 1 < N 2θ iθ i = θ rθ rθ i θ rCladdingCoreCladdingFigure 6.1Light ray traveling through an optical fiberLittle of the light signal is absorbed in the glass core. Therefore fiber optic cables canbe used for longer distances before the signal must be amplified or repeated. Somefiberoptic segments can be many kilometers long before a repeater is needed. Datatransmission using a fiber optic cable is many times faster than with electrical methodsand speeds of over 10 Gbps are possible. Fiber optic cables deliver more reliabletransmissions over greater distances, although at a somewhat greater cost. Cables of thistype differ in their physical dimensions and composition and in the wavelength(s) of lightwith which the cable transmits.6.1.1 Applications for fiber optic cablesFiber optic cables offer the following advantages over other types of transmission media:• Light signals are impervious to interference from EMI or electricalcrosstalk.• Light signals do not interfere with other signals. As a result, fiber opticconnections can be used in extremely adverse environments, such as in liftshafts or assembly plants, where powerful motors produce lots of electricalnoise.• Optical fibers have a much wider, flat bandwidth than coaxial cables andequalization of the signals is not required.• The fiber has a much lower attenuation, so signals can be transmitted muchfurther than with coaxial or twisted pair cable before amplification isnecessary.• Optical fiber cables do not conduct electricity and so eliminate problems ofground loops, lightning damage and electrical shock when cabling in highvoltageareas.• Fiber optic cables are generally much thinner and lighter than copper cable.• Fiber optic cables have greater data security than copper cables.• Licensing is not required, although a right-of way for laying the cable isneeded.6.2 Fiber optic cable componentsThe major components of a fiber optic cable are the core, cladding, buffer, strengthmembers and jacket, as shown below. Some types of fiber optic cable even include aconductive copper wire that can be used to provide power to a repeater.