 - A photonic (or optical) network is a communications network in which information is transmitted entirely in the form of optical or infrared transmission(IR) signals. In atrue photonic network, every switch and every repeater works with IR or visible-lightenergy. A recent development in this field is the erbium amplifier. Conversion toand from electrical impulses is not done except at the source and destination (origin andend point).Optical or IR data transmission has several advantagesover electrical transmission. Perhaps most important is the greatly increased bandwidth provided by photon signals. Because the frequency of visible or IR energyis so high (on the order of millions of megahertz), thousands or millions of signals canbe impressed onto a single beam by means of frequency division multiplexing (FDM). In addition, a single strand of fiber can carryIR and/or visible light at several different wavelengths, each beam having its own set of modulating signals. This is known as wave-division multiplexing (WDM). A subtle, but potentially far-reaching, advantage ofphotonic systems over electronic media results from the fact that visible and IR energy actually moves several times faster than electricity. Electric current propagates at about 10 percent of thespeed of light (18,000 to 19,000 miles or 30,000 kilometers per second), but the energy infiber optic systems travels at the speed of light in the glass or plastic medium, which isa sizable fraction of the speed of light in free space (186,000 miles or 300,000kilometers per second). This results in shorter data-transmission delay timesbetween the end points of a network. This advantage is especially significant in systems where the individual computers or terminals continuously share data. It affects performance at all physical scales, whether components are separated by miles or by microns. It is even significant within microchips, a phenomenon of interest to research-and-development engineers in optical computer technology.
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09 Apr 2007
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