So far, communications systems have managed to keep up because the volume of phone calls, Web pages and videostreams that optical fibers can carry is doubling every nine months, thanks in large part to the ability to squeeze more wavelengths of light into each fiber (See ” Wavelength Division Multiplexing “, TR March/April 1999). It is this remarkable growth in capacity that prevents your favorite MP3 recordings and webcasts from causing gridlock on the Internet.
The problem is that while optical fibers are carrying more and more information, when this speeding light reaches the networks’ central hubs, it must still be converted into electrons and switched by bulky and expensive electronic switches and then converted back to light signals. Converting pulses of information from light into electrons worked fine when fiber optics carried only one signal over limited distances. But electronics have difficulty keeping up as the optical signals become more complex. In the current data maelstrom, the capacity of electronic switches is quickly being outpaced by that of the fiber-optic cables connecting the hubs. In the parlance of optical networking, this data jam waiting to happen is called the electronic bottleneck. “It’s almost a law of nature that any kind of electronic box at the end of the fiber won’t be able to deal with the kind of bandwidth coming out of it,” says David Bishop, director of micromechanical research at Lucent Technologies’ Bell Laboratories.
Enter the new breed of photonic switches-of which at least a dozen are on the way to market. These switches skip the step of converting light into electrons to switch the beams, and, unlike electronics, all-optical devices can deftly redirect even the most complex light streams. All the approaches being tried rely on shrinking the switch components. But after that, it’s a technology free-for-all. Some, like Agilent, employ columns of glass called waveguides to shuttle the light to and from a switch. In the Agilent switch, bubbles deflect the light between crisscrossing waveguides; optical-fiber giant Corning is attempting to use liquid crystals-the same light-bending materials found in your cell phone and calculator readout-to redirect the beams. At Bell Labs, Bishop and his coworkers use arrays of tiny tilting micromirrors to manipulate hundreds of beams at the same time; some 256 of these micromirrors fit on a few square centimeters of silicon.
For those hoping to supply tomorrow’s optical communications equipment, offering some version of these switches is critical to staying competitive. “You either have a technology in this space or you plan to be marginalized,” says Bishop. “There’s a huge amount of money at stake.”
Indeed, network operators are already beginning to install the first generation of these photonic switches, using them much like the mechanical switches in a busy railroad terminal. One immediate advantage is that telecom providers will be able to reconfigure their networks on the fly rather than having to send out technicians to patch a maze of optical fibers. If a backhoe in Des Moines takes out MCI’s Denver-to-Chicago line, tiny tilting mirrors may be all it takes to divert billions of data packets around the break. Operators will also be able to offer dedicated circuits linking a client’s corporate headquarters to its manufacturing plants and customers. In the jargon of telecommunications it’s called provisioning. “Today, it is a manually intensive process that takes months. The ability to do that at the software level is incredibly attractive,” says Yankee Group optical networking analyst Alex Benik.
But that may only be the start. As photonic switches become even smaller, more functional and cheaper, many experts believe they could help bring the massive bandwidth of the network core closer to end users. “As this technology becomes more readily available, the high-speed pipes will extend further and further into the network,” says David Andersen, R&D director for Agilent’s optical networking division. “As that bandwidth becomes available the experience of the Internet will become richer and richer.”