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Indian physicist leads findings on fibre optics

Ela Dutt
India Abroad Correspondent in Washington

Scientists from Lucent Technologies' Bell Labs, led by physicist Partha Mitra, have calculated the maximum amount of information that can be transmitted through optical fibre, demonstrating that fibre optics technology will result in robust, long-term and scalable communications networks.

The Bell Labs team, whose scientific results appear in the latest issue of the British journal Nature, determined that it is theoretically possible to send approximately 100 terabits of information, or roughly 20 billion one-page e-mails, simultaneously per strand of fibre.

As demand for services like high-speed Internet access continues to grow and bandwidth-hungry applications like video-on-demand become increasingly popular, optical fibre will be able to keep up with the demand for these services and those yet to be imagined, Lucent said in a release.

The company noted that as networks continue to make communication faster, smaller, cheaper and smarter in the next decade, there will be an even greater emphasis on fibre optics technology.

Mitra, who is a BSc in Physics from Presidency College, Calcutta (1986-89), and a PhD in Physics from Harvard University (1989-93), has published numerous articles in noted scientific journals.

Involved with the 'theoretical physics' research group at Bell Labs, Mitra says that his research interests include the understanding of complex biological and man-made systems.

"My scientific agenda is strongly data driven, and a large part of the research deals with analysing large data sets with modern statistical and machine learning techniques."

Mitra says he believes that many of the fundamental things to be understood in biological systems are of the nature of 'engineering' or 'design' principles, and his current research spans the understanding of such principles in neural systems and animal behavior as well as in man-made engineered systems like fibre optic communications and multi-antenna wireless.

Mitra has strong research collaborations with colleagues at Caltech, NYU, Princeton, Rockefeller University and the University of Minnesota.

While current commercial optical systems can transmit just under two terabits of information per second and laboratory experiments have demonstrated transmission rates of 10 terabits per second, it has been difficult to theoretically calculate how much information can be transmitted over a glass fibre because the physical properties of glass make light transmitted over fibre susceptible to scrambling in a very complicated fashion.

For example, the speed of a light signal travelling through fibre 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 'non-linear' response.

These non-linear effects cause part of a signal travelling through the fibre to turn into noise. As a result, calculating the exact amount of information that can be sent over a fibre becomes a challenge.

The Bell Labs scientists, led by Mitra, used 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 light waves of different colours are simultaneously transmitted over the same fibre, allowing more information to be sent -- and estimated how much information can be conveyed from a transmitter to a receiver.

They found that if a signal is sent with too little power, the signal will be overcome by the noise in the system.

On the other hand, sending a signal that is too powerful will interfere with other signals. With wavelengths and values typically used in communication networks, the scientists determined that it is theoretically possible to send 100 terabits of data per second without excessive noise or interference.

In an accompanying commentary in the same issue of Nature, Joseph Kahn of the University of California at Berkeley and Keang-Po Ho of the Chinese University of Hong Kong describe the Bell Labs research as 'a useful step towards working out the limits to the spectral efficiency of optical fibres'.

"This paper highlights the fundamental understanding of the ultimate capacity of fibre," said Alistair 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."

With 30,000 employees in 30 countries, Bell Labs is considered the world's largest R&D organisation dedicated to communications and the leading source of new communications technologies.

It has generated more than 28,000 patents since 1925 and has been involved in inventing or perfecting key communications technologies, including transistors, digital networking and signal processing, lasers and fibre optic communications systems, communications satellites, cellular telephony, electronic switching of calls, touch-tone dialing, and modems.

Bell Labs scientists have received six Nobel Prizes in Physics, nine US Medals of Science and six US Medals of Technology.

Lucent Technologies, headquartered in Murray Hill, NJ, designs and delivers the systems, software and services for next-generation communications networks for service providers and enterprises.

Backed by the research and development of Bell Labs, Lucent focuses on high-growth areas such as broadband and mobile Internet infrastructure; communications software; Web-based enterprise solutions that link private and public networks; and professional network design and consulting services.

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