Holograms control data beams

By Chhavi Sachdev, Technology Research News

Infrared light does the work for you when you change a television channel using a remote control. It wasnít always that way; an ungainly cable connected the first clickers to the television set.

Researchers at Pennsylvania State University are looking to make infrared wireless computer networks better competition for cabled networks by harnessing the light channeling abilities of holograms.

Infrared light is very fast. It can transmit data at several times the rate of today's cable-bound networks, and far more than wireless radio networks. Infraredís main drawback, however, is that the light signals must have a clear path to travel.

While radio frequencies can go through walls, infrared signals are limited to line-of-sight contact. A person walking in front of a remote control, for instance, will block the signal. Both radio and infrared waves are also prone to data transmission delays and signal distortions.

The Penn State system addresses the line-of-sight and distortion problems by passing the infrared signals through a hologram, which scatters them towards the ceiling. "The [holographic element] at the transmitter splits a single laser beam into many beams aimed at different directions in such a way that a regular grid of small size light spots is created on the ceiling," said Mohsen Kavehrad, a professor of electrical engineering at Penn State.

The infrared signals then reflect back down to the receivers at different angles. A 10-by-10 grid will allow the signals to cover an average-sized square room, and more than one grid can be used to cover larger rooms, Kavhrad said.

In contrast, existing infrared networks use a single, wide-pattern laser beam that shines on the walls and ceilings. The light-signals reach the receiver at different times after bouncing off several surfaces and traveling different distances. This jumble of signals causes distortion.

The Penn State receiver is tuned to recognize each angled signal, but uses just one at a time to receive data. "The transmitting pattern and the receiving pattern are matched in such a way that the receiver receives signals from only one or two light spots," said Kavehrad. This eliminates the usual signal distortion at the receiver, he said.

The receiver hologram also acts like a curved mirror, concentrating the signal. Unlike a regular mirror, however, the hologram channels only a narrow range of light wavelengths, or colors. This filters out background light, which can also distort signals, said Kavehrad.

Radio-based devices like IBMís Bluetooth transmit data at less than 1 megabit per second, and common ethernet cable transmits data at 100 megabits per second. The infrared network's theoretical capacity is 2,000 megabits, which translates to several hundred megabits per second in practice, Kavehrad said.

The system also does not use much power; it requires less than a watt of power to operate, said Kavehrad.

This research is a nice advance, said Joseph M. Kahn, a professor in the department of electrical engineering and computer sciences at the University of California at Berkeley. "Itís an interesting application of technology to generate those narrow beams," he said.

There is also an issue of where infrared fits in competitively with radiowaves, he said. Although infraredís high transmission rate opens up possibilities, it is still a drawback that the signals cannot pass through walls and so require an access point in each room, he said. "Typically, people are looking to cover a building or a larger geographical area at the lowest cost rather than trying to bump the highest data rate. So at the current stage, people would prefer... radio solutions," he said.

If people wanted high data rates of 100 megabits per second in each room, infrared would play a role, he said. "But the demand isnít there yet."

The system could be commerically available in about a year, said Kavehrad. The researchersí immediate goal is to install a system in their own lab.

Kavehradís colleague was Svetla Jivkova, a research associate at Penn State. They published the paper in the proceedings of the 5th World Conference on Systemics, Cybernetics and Informatics (ISAS/SCI 2001) held in Orlando, Florida between July 22 - 25, 2001. The research was funded by the National Science Foundation (NSF), Pittsburgh Digital Greenhouse and IBMís Shared University Resources programs (SUR).

Timeline:  1 year
Funding:  Corporate; Government
TRN Categories:  Wireless Communication
Story Type:   News
Related Elements:  Technical paper, "Some Recent Advances in Indoor Broadband Infrared Wireless Communications," presented at the ISAS/SCI-2001, Orlando, Florida, July 2001.


October 17, 2001

Page One

Atom laser fits on a chip

Email takes brainpower

Teamed computers drive big display

Holograms control data beams

Pressure produces smaller circuits


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