Bandwidth in communications is like closet space in your home-you can never have enough. And Internet traffic is making the demand for communication capacity grow faster than the wardrobe of a teenager with a no-limit credit card. Bandwidth-hogging megabytes of animated graphics are replacing compact e-mail messages. Data, video and voice signals crowd transmission systems that had ample space just a few years ago. The communications industry needs room to breathe.
That’s exactly what a new generation of fiber-optic technology is bringing to networks such as the aptly named Project Oxygen. Neil Tagare, founder of the CTR Group in Woodcliff Lake, N.J., picked that name for the global network because he considered the tremendous bandwidth offered by the new technology to be as vital for telecommunications as oxygen is to life itself. By sending signals at 16 different wavelengths through each of four pairs of optical fibers, Project Oxygen will carry 640 gigabits per second (Gbit/s) across whole oceans. That’s the equivalent of 10 million simultaneous telephone conversations-enough for every person in Hungary or Belgium to call the United States at the same time.
The technology that makes this new bandwidth possible is called wavelength division multiplexing, or WDM, and it represents the second major fiber-optic revolution in telecommunications. The first came during the 1980s, when telephone companies laced the United States and other countries with fibers to create a global backbone of information pipelines that could carry vastly more data than the copper wires and microwave links they replaced. WDM takes this advantage a giant step further-multiplying the potential capacity of each fiber by filling it with not just one but many wavelengths of light, each capable of carrying a separate signal.
Wavelength division multiplexing has emerged “quite conveniently, as older fiber cables were getting filled,” says Richard Mack, vice president at KMI Corp., a Newport, R.I.-based market analyst firm specializing in fiber optics. Taking advantage of WDM, long-distance carriers such as AT&T and MCI have been able to avoid laying expensive new cables; instead, they simply pump additional wavelengths through existing fibers.
The WDM revolution has arrived with unanticipated swiftness. A decade ago, Mack points out, “people said there was a glut of fiber capacity.” To allow room for expansion, phone companies had laid cables containing 24 to 36 fibers, many held in reserve as “dark fibers.” Each fiber carried hundreds of megabits per second at a single wavelength. Since then, carriers have raised data rates to 2.5 Gbit/s and lit most of the dark fibers. But the tremendous increase of traffic has crowded these cables that once seemed so voluminous. The closets, it seems, are rapidly being packed to the rafters-and stuff is spilling out onto the floor. Telephone usage accounts for some increase, including the spread of fax machines and mobile phones. But the most dramatic growth has been from Internet traffic, which roughly doubles each year.
What’s also clear is that there’s no end in sight to the soaring demand, especially if, as many experts believe, two-way video communication becomes more common. “The communications industry is undergoing a transition that in a few years shall bring us digital video for our everyday use at home and at work,” says Shahab Etemad, who heads WDM transmission development at Morristown, N.J.-based Bell Communications Research, or Bellcore. (Initially the research arm of the local and regional phone companies, Bellcore now operates as a network management consultancy with a variety of corporate clients.) Etemad expects the change from voice telephony to digital data heavy with video to require multiplying backbone transmission capacity by about a factor of 200-and, he insists, WDM “has to play the leading role” in meeting that expanded demand.
Thanks to advances in WDM methods, fiber has done a good job in keeping up with this explosion in demand. According to David Clark, senior research scientist at MIT’s Laboratory for Computer Science, “The ability to get bits down a fiber is growing faster than Moore’s Law,” which predicts the doubling of computing power every 18 months. At the moment, Clark notes, the carrying capacity of fiber is doubling every 12 months.