Tunable Lasers: (Must Read for laymen)
Optical Tune: Adjustable Lasers
By Joe McGarvey, Inter@ctive Week
February 7, 2000 7:02 AM ET
It's only a slight exaggeration to suggest that optical
networking technology is developing at the speed of
light. Almost as soon as one innovation can be
introduced, another breakthrough is poised to push the
already white-hot sector of the networking industry to a
new plateau.
The current innovation-in-waiting is the concept of a
tunable laser, which holds the promise of providing
carriers with another steppingstone toward the
construction of an all-optical network.
"Once this technology is credible and available from
commercial vendors," says Tom Koch, director of the
photonic circuits division at Lucent Technol-ogies' Bell
Labs, "network architects will be able to let their
imaginations run wild."
Lasers are optical networking components used by
bandwidth-multiplying devices known as Dense
Wavelength Division Multiplexing gear. DWDM devices
use lasers to carve out separate beams of light, or
wavelengths, across a single strand of fiber-optic
cabling. Each laser in a DWDM system creates a
separate wavelength.
Currently, lasers operate at a fixed frequency. In other
words, a laser designed to create a wavelength at 1,520
nanometers cannot be reprogrammed to create a light
channel at 1,565 nm of the frequency spectrum. A
tunable laser, as the name suggests, can be adjusted to
operate at a variety of frequencies.
The most immediate benefit of a tunable laser, experts
say, is the ability to enable service providers to reduce
inventory levels.
"With a tunable laser, one size fits all," says Connie
Chang-Hasnain, chairwoman and chief technical officer
at Bandwidth9, which makes tunable lasers. "One
component could be used across any number of
channels."
Because lasers are tuned for a single frequency, service
providers must keep excessive amounts of inventory to
make sure each laser in a DWDM device has a backup
that works at the same frequency. As the channel
capacity of DWDM gear increases, the problem
magnifies.
"As you hit 160 channels, you don't want to have to keep
160 separate lasers in inventory," says Basil Garabet,
senior vice president of marketing and sales at Altitun.
Altitun, which is based in Sweden, recently announced a
trial of its tunable laser technology with Telenor, a
Norwegian service provider.
While the ability to reduce inventory and operational
costs is the most immediate benefit of tunable lasers,
the technology also offers the potential to provide a
hyperfast method for service providers to move data
across their networks.
In the metropolitan environment, lasers that can be
remotely programmed to change wavelengths could be
deployed to add flexible bandwidth in the access portion
of the network. "If you want to drop off a wavelength in
one area," says Lynn Hutcheson, an analyst at the Ryan
Hankin Kent research firm, "you can simply remotely
tune the laser to a new wavelength."
Tunable lasers would also be beneficial to the makers of
optical switches, which are able to divert wavelength
across the network by switching a wavelength from an
incoming port to an outgoing port in the switch. While
this type of wavelength manipulation currently re-quires
the optical signal to be converted to an electronic signal
- a time-consuming and expensive process - tunable
lasers would make it possible to do the wavelength
switch without converting the signal.
The major potential of tunable lasers, however, is the
ability to route information on a more granular level than
wavelengths, Koch says. Lucent, as well as scientists
as the Sprint Advanced Technology Laboratories, is
experimenting with using tunable lasers to route
information on a packet-by-packet basis, which is the
method used by routers and switches.
Commercial products that route packets in the optical
domain are still several years off, according to Koch.
Although Lucent has already produced a four-channel
tunable laser, equipment capable of routing packets by
changing lasers to a new wavelength would have to
change frequencies much faster than today's tunable
lasers, he adds.
"If the idea is to send one packet to a new destination by
changing the wavelength," Koch says, "you'd have to
change wavelengths in time to process the next packet."
As far as the availability of tunable lasers capable of
switching information at the wavelength level, Hutcheson
estimates that the first wave of commercially available
systems based on tunable lasers will hit in roughly 18
months. Although Hutcheson estimates that Altitun is
probably the company furthest along in production, he
says that virtually every optical component maker is
working on a tunable laser.
While Altitun must compete with Bandwidth9, Lucent
and optical start-up Agility Communications in the
na-scent market, it will also face competition from
Alcatel, JDS Uniphase, Nortel Networks and others.
"Tunable lasers hold the potential of being a significant
technology," Hutcheson says. "Developers, however, still
have to prove they can deliver reliability and
performance."
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