Some Glass!

Scientists at Lucent Technologies’ Bell Labs have calculated the maximum

amount of information that can be transmitted over optical fiber, demonstrating

that fiber optics technology will result in robust, long-term and scalable

communications networks.

The Bell Labs team determined that it was theoretically possible to send

approximately 100 terabits of information, or roughly 20 billion one-page

e-mails, simultaneously per strand of fiber.

As demand for services like high-speed Internet access continues to grow and

bandwidth-hungry applications like video-on-demand become increasingly popular,

optical fiber will be able to keep up with the demand for these services and

those yet to be imagined.

"As networks continue to make communication faster, smaller, cheaper and

smarter in the next decade, there will be an even greater emphasis on fiber

optics technology," said Rod Alferness, senior vice president of optical

networking research at Bell Labs. "As we light more optical fiber, and

couple this with all-optical switches, we will continue to improve the speed and

quality of metropolitan and backbone networks, helping to enrich the end-user

experience."

While current commercial optical systems can transmit just under two terabits

of information per second and laboratory experiments have demonstrated

transmission rates of 10 Tbps, it has been difficult to theoretically calculate

how much information can be transmitted over a glass fiber. This is because the

physical properties of glass make light transmitted over fiber susceptible to

scrambling in a very complicated fashion. For example, the speed of a light

signal traveling through fiber depends on the intensity of the light and is not

a constant as it would be in free space; physicists refer to this behavior as a

‘non-linear’ response. These non-linear effects cause part of a signal

traveling through the fiber to turn into noise. As a result, calculating the

exact amount of information that can be sent over a fiber becomes a thorny

challenge.

The Bell Labs scientists were able to simplify the challenge by using an

analogy from quantum physics, together with ideas from information theory. They

looked at telecommunication systems that use wavelength division multiplexing–a

technique by which lightwaves of different colors are simultaneously transmitted

over the same fiber, allowing more information to be sent–and estimated how

much information could be conveyed from a transmitter to a receiver. They found

that if a signal was sent with too little power, it would be overcome by the

noise in the system. On the other hand, too powerful a signal would interfere

with other signals.

With wavelengths and values typically used in communication networks, the

scientists determined that it was theoretically possible to send 100 terabits of

data per second without excessive noise or interference.

"This paper highlights the fundamental understanding of the ultimate

capacity of fiber," said Alastair Glass, chief technical officer of Lucent’s

optical networking group. "It says that we are still a long way from the

fundamental limits in current commercial systems, and it’s still uncertain

when optical systems will be able to approach the theoretical limits."

BUSINESS WIRE