Bell Labs' high-bandwidth wireless prototype could have military uses
- By William Jackson
- Mar 15, 1999
Improving on government satellite communications, scientists at Lucent
Technologies Inc.s Bell Labs have pushed wireless data at 10 Gbps more than two
miles through the Earths atmosphere.
Bell Labs of Murray Hill, N.J., used dense wavelength division multiplexing (DWDM) and
powerful optical amplifiers to achieve the 10-Gbps rate, outstripping current commercial
wireless optical systems by an order of magnitude.
The government is committed to the technology in space, said Jim Auborn,
director of photonics programs for Lucents government solutions group.
The high-bandwidth prototype could set up short hops and line-of-sight links where
fiber-optic cable would be impractical or too expensive. The primary market likely would
be in rapid military deployment, Auborn said.
Even high-powered wireless optical systems are impractical for long links now because
of their limited range. The Navy is testing a 155-Mbps Synchronous Optical Network OC-3
wireless system between an aircraft carrier and a shore facility in San Diego, Auborn
Weather interference also limits wireless opticals ability to substitute for
fiber cabling. But strong signals, range and bandwidth could make wireless optical viable
for more applications.
DWDM uses four different light wavelengths to set up four distinct channels. Auborn
said developers plan to boost the Lucent prototype from four 2.5-Gbps channels to eight
and then 16 10-Gbps channels.
Because it does not use radio waves, wireless optical needs no operating license and is
more secure than radio-frequency wireless, he said.
The tightly focused optical beam has a footprint of 2.2 meters over 4.4 kilometers,
making it hard to intercept.
Wireless optical technology is nothing new. Alexander Graham Bell invented it in 1880
by transmitting a telephone signal 600 feet over a focused light beam reflected off a
microphone diaphragm. The Lucent prototype uses custom telescopes, standard optical
transmitters and receivers, and rare-earth amplifiers.
Rare-earth metals, erbium and ytterbium, photochemically amplify the light signal up to
several watts; Auborn said conventional amplifiers produce only a few dozen milliwatts.
In the vacuum of space, such a system could transmit a single-mode signal about 84,000
kilometers between satellites. In Earths atmosphere, a multimode signal is necessary
to carry data error-free over a much shorter distance.
William Jackson is a Maryland-based freelance writer.