Light flashing through optical fibers forms the backbone of today’s high-speed telecommunications networks. It’s the technology that makes possible the Internet as we know it, and, in the not-too-distant future, it could make possible an “all-optical Internet”(see “The Microphotonics Revolution,” TR July/August 2000). Relying totally on fiber optics to transmit data, an optical Internet will offer enough bandwidth to deliver far more compelling online entertainment, education and e-commerce; there will even be sufficient bandwidth to hold video conferences in which the slightest changes in facial expression-and perhaps even smell and touch-are immediately apparent.
One hang-up in transmitting light signals through fiber optics, however, is that the light tends to peter out over distance. Every 70 kilometers or so in an optical fiber, amplifiers are needed to boost the signals. These devices are expensive and can break down; if that happens, say, in the middle of an optical cable buried in the Pacific Ocean, it’s a costly headache. What’s more, as telecommunications companies look to push more and more data through fiber optics, by squeezing multiple wavelengths of light within a single fiber (see “Wavelength Division Multiplexing,” TR March/April 1999), amplifiers are having a tough time keeping up with the complexity of the signals.
With that in mind, researchers at Lucent Technologies’ Bell Labs have developed a new generation of optical amplifiers that take advantage of a well-known effect in laser physics called Raman scattering. Raman amplifiers are based on a rather improbable premise: to amplify a light beam, blast the medium through which it is traveling, using another beam coming from the opposite direction. (C. V. Raman won the 1930 Nobel Prize in physics for observing the general effect.) In the latest version of Raman amplification, Lucent has developed a device that uses multiple lasers to boost light signals in an optical fiber, allowing the signals to travel much farther before they need to be boosted again. In addition, this newest design should make it possible for amplifiers to keep up with the all-optical Internet that’s on the horizon.
A 1999 patent issued to Lucent describes a new type of Raman amplifier that is “used in almost all the new ultralong-distance systems being developed,” says coinventor Kenneth Walker. In last year’s patent, Bell Labs researchers led by Walker and Andrew Stentz followed up with the invention of a “multiple-order” Raman amplifier that adds a second laser pump; the lasers work in tandem to extend the duration of light signals traveling through an optical fiber. The design is also capable of working with future optical transmission equipment that will transmit data over a greater portion of the optical spectrum to boost bandwidth even further. Both versions exploit an inherent advantage of Raman amplifiers: they disrupt the data carried by light much less than other methods of amplification do, thus eliminating costly equipment used to correct the signals.
The recent design improvements from Bell Labs and others are now catapulting the technology into the mainstream of telecommunications. According to Strategies Unlimited, an analyst firm in Mountain View, CA, Raman amplifiers could grow from a fraction of the $3.3 billion optical amplifier market at year’s end 2000 to about half the total $7.3 billion market in 2004.
The all-optical Internet is still a few years away. But when it arrives, Lucent’s latest version of Raman amplification may be one of its building blocks, bringing more bandwidth directly to your desktop and your handheld wireless device.