QuickStudy: Optical networking

Computerworld - Remember those World War II Navy movies where a sailor on one ship signaled to another by flashing Morse code with a large, shutter-equipped spotlight? The receiving ship then flashed the same message to the next ship in the fleet. That's digital optical transmission, and it's essentially how an optical network works.

After decades of development, optical networks have emerged as feasible alternatives to traditional copper cabling or wireless networks, offering much greater capacity and higher transmission speeds along with the ability to handle multiple simultaneous transmissions. The first main market for optical networking will be traditional telecommunications networks.

Why Optical?

Two words explain the trend toward optical networking: capacity and speed. Today, a good Category 6 copper network cable can carry a single data transmission at a rate of 1G bit/sec. An optical fiber as thin as a human hair can handle multiple transmissions simultaneously at speeds of more than 10G bit/sec., and it's getting faster.

Several factors contribute to the differential. Light travels many times faster than electrons, and photons don't interfere with one another the way electrical signals do.

At the heart of optical networking is optical fiber, which consists of a narrow thread of glass—actually pure silicon dioxide—that's been clad with another glass that has a different index of refraction. A light signal introduced into the central fiber is reflected off the edges of the fiber as it travels along its length and thus doesn't disperse or scatter. Still, impurities in the fiber eventually absorb some fraction of the light, causing signal degradation. This requires the use of repeaters that receive a signal and amplify it before sending it over the next fiber segment.