UNDERSTANDING FIBER OPTICS
Bandwi d th Bandwidtihsameasuroefthedata-carryincgapacitoyfanopticalfibe.rItisexpresseadstheproducotffrequencaynddistanceF.or example, a fiber with a bandwidth of 500 MHz.km (Mega-hertz kilometer) can transmit data at a rate of 500 MHz along one kilometer. Bandwidth in singlemode fi bers is much higher than in multimode fi bers:
• multimode case
• singlemode case
A B C A B C
AABABCBCC AAABBBCCC
A B C A B C
A B C A B C
mode 1
mode 2
mode 3
Information (A, B or C) is propagated in fiber according to only one mode, therefore is not deformed. It is thus possible to closer the information, i.e. to obtain a much more important flow.
Information (A, B or C) is propagated in fiber according to N modes (paths), which deform it, as if it were “duplicated” N times (for example on the diagram above, the mode 3 path is longer than the mode 2 path, which is itself longer than the mode 1 path). If information is too close one to the other, there is a risk of mixing, and it will not be recoverable at the exit of fiber. That is why it is necessary to space it sufficiently, i.e. to limit the flow.
WHYTOCHOOSE FIBEROPTICS? The main benefits of fiber optics are:
•Lower loss: Optical fiber has lower attenuation than copper conductors, allowing longer cable runs and fewer repeaters. • Increased bandwidth: The high signal bandwidth of optical fiber provides a significantly greater information-carrying capacity. Typical bandwidths for multimode fibers are between 200 and 600 MHz.km, and > 10 GHz.km for singlemode fibers. Typical values for electrical conductors are 10 to 25 MHz.km. •Immunity to interference: Optical fibers are immune to electromagnetic and radio frequency interference and also emit no radiation themselves. •No detection: Standard fiber optic cables are dielectric, so they cannot be detected by any type of detector. •Electrical isolation: Fiberoptics enable stotransmint formatiobnetweetnwopointsattwo different electrical potentialsa,nd also next to high voltage equipments. •Decreased size and weight: Compared to copper conductors of equivalent signal-carrying capacity, fiber optic cables are easier to install, require less duct space, and weight about 10 to 15 times less.
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