Getting In Tune
Optical vendors tout tunable laser advancements
By David Iler
from the May 21, 2001 issue of Broadband Week
The need for speedy, flexible optical network technology has not diminished with the recent economic blues, and the next generation of optical lasers is seen as a way to get more bang for the buck out of present and future network topologies.
Accordingly, several companies, both entrenched networking stalwarts and up-and-coming startups, have announced new tunable laser technologies and are preparing to ramp up their manufacturing capacities.
Nortel Networks and ADC Telecommunications have added tunable lasers to their portfolios via acquisitions, with Nortel buying Coretek and ADC snapping up Altitune in deals announced last year.
Startup Atoga Systems recently announced a router upgrade that integrates tunable laser functionality with legacy system interfaces, while Agility Communications in April invested $1 million in Brooks Automation to beef up its Santa Barbara, Calif., optical component manufacturing plant.
The new generation of lasers contrast with traditional fixed wavelength lasers because they can produce and transmit optical signals at more than one frequency. "The reason why tunables is such a hot space is there's been a fundamental change in the market over the last four or five years with Dense Wave Division Multiplexing," says Arlon Martin, Agility's vice president of marketing.
DWDM enables transmission of multiple optical channels down the same fiber at the same time. But in today's networks, an eight-channel DWDM system requires eight fixed lasers to produce signals for each channel or frequency, for example at 1531 nanometers. With DWDM gear now capable of delivering 100 or more channels, the corresponding number of fixed-bandwidth lasers required to take advantage of DWDM can be staggering.
Add to that spare lasers needed for each frequency to kick in when one fails, and the number of required fixed lasers grows even more. With fixed-wavelength lasers, changing frequencies of a particular DWDM channel means an operator must send out a technician to physically change transponder line cards at the central office, node or cross-connect. The promise of tunable lasers, says Martin, is to "move from a truck roll to a 'mouse roll,'" that is, to provision new channels and switching frequencies remotely through software.
Because tunable lasers are designed to switch individually from one color of light or frequency on the fly, network planning and frequency allocation in theory become easier and less costly. Tunable lasers, Martin says, "provide far more bandwidth at far less cost." Additionally, tunable lasers help to make so-called dynamic provisioning a reality by looking for free and open DWDM channels. As DWDM systems push the envelope to deliver more and more channels, tunable lasers are being viewed as an economical way to take advantage of the full power of DWDM with less hardware.
In the short term, says Marc Liggio, vice president of broadband research for Allied Business Intelligence, the market for tunable lasers will focus on using the devices for sparing, or backing up, frequencies in case of failure. To compensate for the average failure rate of lasers, one or two tunable lasers may be used to support a 40-channel DWDM systems, whereas today, 40 fixed-wavelength lasers, each tuned to a specific frequency, must serve as backups. "That's a substantial cost savings," Liggio says.
According to a November 2000 research report from telecommunications industry analyst firm RHK, the market for tunable lasers is one of the fastest-growing segments in optical components for terrestrial dense wavelength division multiplexed (DWDM) networks. RHK forecasts this market to grow from almost zero revenue in 2000 to $1 billion in sales by 2004.
The market for tunable lasers is expected to be robust, partly because they are a replacement technology for what's out there right now, instead of a brand-new technology, as Tom Dudley, vice president of sales and marketing for Nortel's optical components division, points out. He expects the growth in adoption of tunable lasers to exceed the growth of the total optical components market.
As tunable lasers mature, said Liggio, they will be used to support more sophisticated applications, such as packet switching and dynamic provisioning. Instead of dedicated point-to-point circuits based on specific DWDM frequencies, tunable lasers allow for a greater degree of flexibility. These lasers, says Rob Plastow, chief technology officer for ADC's fiber optic division, can "change where the capacity is allocated in the network." As individual wavelengths are dropped off at switch locations, those frequencies can be re-used further down the transmission path as tunable laser systems integrated into switches recognize the open channel.
"The use of tunable lasers greatly simplifies the size of the switch in an optical cross-connect," says Plastow. The benefit is the ability to switch any wavelength onto any fiber coming into and leaving the cross-connect. Meanwhile, the race is on to bring tunable lasers to market in volume.
Agility, according to Martin, expects to be able to produce 1,000 tunable lasers per week by the end of this year, depending on market demand.
"Our (tunable laser) design allows for a tremendous level of scalability in manufacturing," says Nortel's Dudley. Nortel's tunable lasers and filters use micro-electromechanical system-based technology, and Dudley says the testing time for the lasers, a key factor in the manufacturing process, can be completed in a few minutes per device. "The whole market is going to be capacity constrained," says Plastow. "Anybody who makes these things in volume will win (early market share)."
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