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| Optical Networks |
Optical Networks
An optical network is an network in which the physical layer technology is fiber-optic cable. Cable trunks are interconnected with optical cross-connects (OXCs), and signals are added and dropped at optical add/drop multiplexers (OADMs). The holy grail is an all-optical network. In this scheme, an optical wavelength (which acts like a data circuit) stays in the optical realm from end to end. In contrast, most optical networks have implemented OEO (Optical Electrical Optical) switches, which convert optical signals to electrical signals for processing, and then back again to optical signals for the next leg of the trip. The optical-to-electrical conversion adds delay and introduces possible errors as the signal are converted, moved up the protocols stack, and processed by software or firmware. The all-optical network avoids this process. At this writing, components that make the all-optical network a reality are emerging.
Early optical networks transmitted one signal over a fiber strand. With WDM (Wavelength Division Multiplexing), multiple infrared wavelength signals (Called Lambdas) may be transmitted over a single fiber strand. Today, precision lasers and optical amplifiers allow hundreds and potentially thousands of signals to be transmitted across a single fiber over distances that span continents. These stems are called DWDM (dense wavelength division multiplexing) systems.
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