Getting Tuned Up
I like the "$1.5 billing in the next couple of years" comment!
:-))
Steve
Getting Tuned Up
By Bill Scanlon, Interactive Week
February 14, 2001 7:43 AM PT
URL: zdnet.com
This quarter, most large carriers are testing tunable lasers. These devices speed ones and zeroes
down optical networks and jump from wavelength to wavelength faster than an eyeblink.
The market for tunable lasers is expected to grow from $100 million last year to about $1.5 billion
in the next couple of years, according to the research firm ElectroniCast.
"Everyone is saying that tunable is going to be a winner," says Stephen Montgomery, market
research consultant for optical communications at ElectroniCast. "There's going to be a huge
demand for this stuff over time as copper is replaced by fiber."
Nortel Networks and Lucent Technologies are market leaders, each offering lasers that can tune
to 20 different wavelengths.
But Santa Barbara, Calif., start-up Agility Communications claims the lead in breadth of tunability,
with a laser in trials that can switch between 100 wavelengths. And Altitun, a Swedish start-up
acquired in May by ADC Telecommunications, claims to be the first to market with a tunable laser
that can switch wavelengths in nanoseconds, so fast that it can shuffle packet by packet,
simplifying the switches on optical networks.
Tunable lasers are key to a faster, fatter Internet. They let networks operate at maximum capacity,
switch bottlenecked traffic to uncrowded wavelengths, and potentially can make many costly
optical switches unnecessary.
A fiber-optic strand is just skinny glass until it is "lit" when a laser is turned on and, teamed with a
modulator, starts blinking signals down the thread of fiber.
A fiber strand is thinner than a human hair. Anything that thin seemingly would be doing well
enough to carry just one lane of voice, video and data traffic.
But as demand for bandwidth mushroomed, physicists came up with a lower-cost alternative to
digging trenches and laying more conduits in the ground. They developed Dense Wavelength
Division Multiplexers (DWDM), which use mirrors or bubbles to divide fiber into several
differently colored wavelengths of light.
Each color can carry its own traffic because each has a very precise and never-varying wavelength
— and thus never, or very rarely, bumps into another color's traffic. Carriers are beginning to
deploy DWDM gear that can divide light into as many as 64 wavelengths. In laboratories,
scientists have divided light into more than 1,000 wavelengths.
Each wavelength that carries traffic needs a laser to blink on and off billions of times per second
and bring to life the ones and zeroes that make up the bits and bytes, the e-mails, songs, movies
and charts traveling across a network.
Most lasers on fiber-optic networks today are fixed — that is, once they're assigned to a color,
they stay with it forever. They can't help ease the overflow of traffic if, say, the new Victoria's
Secret online fashion show is planned for the same day as the corporation's big videoconference,
and they're sharing the same overcrowded path through several switching stations.
Tunable lasers, however, switch traffic to wavelengths that aren't overloaded, easing the
bumper-to-bumper conditions.
The goal is a laser that can be tuned across all channels of a DWDM system, but which also can
switch channels in a flash and has the oomph to carry the signal a long distance over the network's
core. So far, most tunable lasers can only perform one or two of these functions.
100 Points of Light
Agility's 100-channel laser is the size of a grain of salt and runs on five volts of power. It can tune
to 100 different channels of light, taking about 10 milliseconds to switch from one channel to
another.
Agility has tested the 100-channel laser with eight companies, including Lucent, Nortel, PhotonEx
and Zaffire, and plans to have it in the hands of a couple of dozen more by the end of the year.
"We're in the lead, but it's a very big market and there are a whole lot of companies that are going
to be chasing it,'' says Arlon Martin, vice president of marketing at Agility.
Altitun says its 80-channel lasers can switch channels in under 10 nanoseconds – and a
nanosecond is 1 million times faster than a millisecond, which is the speed at which most of today's
gear operates.
Altitun makes lasers in four parts, separating the laser's active function of generating the light from
its passive function of defining the wavelength. A grating is etched into the laser to allow for tuning
to different wavelengths. A phase module fine-tunes the wavelength and a coupler transfers some
wavelengths from the bottom to the top of the wave guide. When pumped with electricity, most of
the light spews from the front of the laser and is funneled into the fiber, but some is reflected back
into the laser to be recycled. By changing the current that goes through the etched grating, the laser
can be tuned to any of dozens of wavelengths.
"It has several advantages," says Robert Plastow, chief technology officer at Altitun. "It's a single
chip with no moving parts. Everything is controlled by the current. And it's extremely fast."
Millisecond speed is fine for today's applications, says ElectroniCast's Montgomery, noting that a
millisecond is a lot faster than the time it takes to manually lay another conduit or insert another
card into a 7-foot rack. "The competition is a truck roll."
"Millisecond is not an issue yet. If and when it becomes one, Agility will probably have a solution,"
says Tom Hausken, a senior analyst at Strategies Unlimited.
But Plastow says nanosecond speed, by allowing a network to switch on a packet-by-packet
basis, "will let you utilize the network capacity much more efficiently. It's a year or two out." When
chips can shift wavelengths that fast, the true advantage of a mesh network, combining the
strengths of tunable lasers and optical switches, will emerge.
Carriers are looking for tunable lasers that can handle the shakes, rattles, rolls and temperature
changes in an optical network. However, price is important, too. "They don't want to pay more
than 1.5 or two times the premium of a fixed laser," Montgomery says. "The tunable lasers are
more expensive than that now. They're hard-pressed to get their prices down, but they can do it
with more customers and volume."
Altitun has completed 150,000 hours of tests and has supplied samples of its 80-channel chips to
most of the major carriers in the world, Plastow said.
Changing Their Tune
NTT electronics of Japan also makes tunable lasers that can change from one wavelength to
another in about 10 nanoseconds. Wavelengths in the middle of the spectrum tend to have
stronger signals. NTT uses Super-Structure Grating Distributed Bragg Reflector technology to
correct for that by changing the current and thus changing the amount of light being generated. The
Distributed Bragg Reflector technology uses a device in which light is bounced back and forth
along a horizontal cavity running the length of the laser, ensuring that it resonates at the required
frequency. Grooves etched into the surface of the laser keep the laser beam finely focused.
Lucent's Microelectronics Group touts the fiber-optic industry's first 20-channel continuous wave
tunable laser module for both short- and long-haul high-speed optical networking systems. Lucent
has patented its "wavelength locker'' that locks the laser emission to any of 20 adjacent
50-gigahertz channels. The 1.5-micron Distributed Bragg Reflector laser, called a tunable
electroabsorptive modulated laser, has a booster amplifier and a photo detector.
Marconi makes a Sample Grating Distributed Bragg Reflector, a technology that offers wide
tuning range, but limited power output.
Coretek, which was acquired by Nortel Networks, uses Vertical Cavity Surface Emitting Laser
technology in its tunable laser, bouncing light between two mirrors at either end of a vertical hole
to keep it resonating at the required wavelength. The top mirror has a hole in it to let light escape
into a fiber strand. It operates at millisecond speed.
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