Our taste for the Internet is insatiable – traffic is growing so fast that its transmission systems soon might be filled to capacity. But scientists are coping, finding ingenious ways to satisfy our deep bandwidth hunger.
Of course, they can’t accelerate the speed of light as it flies down the glass fibers of central networks carrying our Internet messages worldwide. The laws of nature limit that. Yet they can tap other characteristics of light to pack layers of information into each optical fiber in the network, so that far more data can flow simultaneously down those glass backbones.
Old systems used light that was either on or off – like flashlight signals – to send information along the fibers in the binary language of zeros and ones. But light is an electromagnetic wave, so it has a whole electrical field that scientists now are putting to work to add to the information on each wavelength.Alcatel-Lucent recently announced a system for telecommunications-service providers that takes advantage of both the polarization and phases of light to encode data. The system can more than double the capacity of a single fiber, said James Watt, head of the company’s optics division. Such a system, for example, can transmit more than twice the number of high-definition TV channels than now can be streamed concurrently.
The new equipment is part of a continued research drive to increase the capacity of each strand of optical fiber, said Keren Bergman, a professor of electrical engineering at Columbia University and head of its Lightwave Research Laboratory. “We are stuffing more information in the same space,” she said.
A fiber is no thicker than human hair, but can carry many wavelengths of laser light, with each wavelength adding to the bits transmitted per second. The bit rates now attainable are in the billions (gigabits) per second or even trillions (terabits) per second.
The need for core network improvement is pressing, said Stojan Radic, a professor of electrical engineering at the UC San Diego. “We are looking at a point soon where we cannot satisfy demand,” he said. “And if we don’t, it will be like going over a cliff.”
Demand is continually growing, somewhere below street level, as details of our e-mail, bank balances and national security zip along on light waves. And consumers can’t get enough video clips on YouTube, television shows on Hulu, and movies streamed to them by Netflix that they watch on their computers and TVs.
That’s just a fraction of the traffic. Add to it the many demands of cloud computing and countless mobile devices and information data bases, for example, and the totals become even harder to imagine.
Next-generation systems that can handle this future traffic jam are being developed by many companies, including Ciena in Linthicum, Md., and Infinera in Sunnyvale. Alcatel-Lucent says it has begun to sell equipment that transmits up to 88 channels of information, each operating at 100 gigabits a second, but it has not disclosed customer names.
The new equipment from Alcatel-Lucent is expected to reduce the cost per transmitted bit of information, compared with existing equipment, said Paul Louis Ross, a company spokesman. The systems are based in part on the work of the researcher Gabriel Charlet, a scientist at an Alcatel-Lucent Bell research facility in France, who last year sent data at a rate of 7.2 terabits a second over a single fiber more than 7,000 kilometers long.
All of those added gigabits take advantage of the complex way that light can be used to encode data. In the past, when only the intensity of light was used, the signals could transmit only one bit per time slot, said Govind Agrawal, a professor of optics at the University of Rochester.
By contrast, in the new system from Alcatel-Lucent, two binary digits or bits can be encoded by using four phases of light. And the polarized light can vibrate up and down or sideways. In this way, four bits of data can be transmitted per time slot instead of one, said Andrew Chraplyvy, a scientist and executive at the Bell Labs of Alcatel-Lucent in Crawford Hill, N.J., where fiber-optic research originated in the 1960s.
Scientists have long known how to use polarization and phases of light to encode information, said Chraplyvy, a winner of the Marconi Prize for his work in communications and information technology. “Although we could do it, we never needed to before, because the capacities we had were enough,” he said. “Now that capacity is running out.”
Adel Saleh, a program manager at the Defense Advanced Research Projects Agency, or Darpa, in Arlington, Va., agreed. “The traffic requirements on the Internet double every two years,” he said. “This is why we are struggling to keep up.”
