optical network (photonic network)

An optical (photonic) network is a communications network in which information is transmitted as optical or infrared radiation transmission (IR) signals. Optical transmission has several other advantages over electrical transmission, including shorter data-transmission delay times.

An optical (photonic) network is a communications network in which information is transmitted as optical or infrared radiation transmission (IR) signals. 

In a true photonic network, every switch and every repeater works with IR or visible-light energy and conversion to and from electrical impulses is only done at the source and destination (origin and end point). Electric current propagates at about 10 percent of the speed of light (18,000 to 19,000 miles or 30,000 kilometers per second), while the energy in fiber optic systems travels at the speed of light. This results in shorter data-transmission delay times between the end points of a network.  The top speed for data running over a single optical channel is about 10 Gbps but greater speeds can be obtained by dividing up a single optical cable into a number of channels.

Optical or IR data transmission has several other advantages over electrical transmission. Perhaps most important is the greatly increased bandwidth provided by photon signals. Because the frequency of visible or IR energy is so high (on the order of millions of megahertz), thousands or millions of signals can be impressed onto a single beam by means of frequency division multiplexing (FDM). In addition, a single strand of fiber can carry IR and/or visible light at several different wavelengths, each beam having its own set of modulating signals. This is known as wavelength-division multiplexing (WDM).

Dynamic provisioning, whereby optical channels can be split into many high-speed wavelengths, allows network managers to increase the capacity of their optical network at very short notice. Instead of having to wait for service providers to dig up roads and lay cable, users can get more bandwidth in days - hours, even - rather than weeks or months. This is one of the reasons optical fibre is widely used in network backbones within buildings, where bandwidth demands are at their highest and where there is the greatest likelihood of electromagnetic interference from other building services, such as high-voltage power cables, which often run close by network cabling.

While it is relatively easy to tap into copper cables and read the data running over them, it is difficult to do this with optical signals running over fibre. Many organizations that need secure networks, such as government and defense installations, already make extensive use of optical networks, sometimes right to the desktop.

See also: erbium amplifier, photonics

This was first published in November 2013

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