See the Light Bounce

Mirrors may hold the key to all-optical networks

Light bouncing off bubbles, tilting off tiny mirrors, refracting through crystals and shifting across holograms.

Cross a seventh-grade science fair with the inventions of Rube Goldberg, add a dash of Dr. Seuss and — behold! — the state of the art in all-optical switches.

Replacing the current generation of switches with true optical ones not only eliminates the bottleneck caused by converting the signal, but creates a network that is more manageable, has much higher capacity, is faster to provision and is capable of supporting all kinds of new services, boosters say. Its not a question of whether to move in the direction of purely optical fabric, but how — and how quickly.

In the rush for bandwidth, optical device purveyors must weigh reliability, speed and throughput against cost and yield. "All engineering choices are trade-offs," says Gary Austin, general manager of Lucent Technologies optical switching division. "The fundamental value proposition is not because its neat technology or optics for optics sake, but because its really the most economical way to build switches."

Lucent has placed its bet on micro-electromechanical systems (MEMS) — micro-electromechanical arrays of tiny mirrors made of silicon that power its WaveStar LambdaRouter. The silicon plates flex on springs, creating motion without friction, Austin says.

As the number of ports increases, the number of cross points in a wave-guide system quickly becomes difficult to manage. A 256-port switch requires more than 65,000 cross points, Austin notes, and a version of the WaveStar LambdaRouter with 1,024 ports is due to ship by midyear. Lucent began testing the WaveStar LambdaRouter last summer on GlobalCrossings next-generation network; tests with four other carriers are ongoing.

Corvis, in Columbia, Md., is one step closer than Lucent to full-fledged deployment of a photonic switch. So says Shyam Jha, Corvis vice president of marketing, who notes that Broadwing, Qwest Communications International and Williams Communications all have Corvis equipment on the job. Broadwing expects to have revenue-generating traffic by the end of March, he says.

Corvis declined to discuss the details of its optical switch, but analysts suspect its similar to Lucents MEMS technology.

Meanwhile, Agilent Technologies took the library of thermal ink-jet patents it inherited from its parent company, Hewlett-Packard, and, working with Alcatel, translated them into a photonic switching technology. The Agilent switch uses bubbles in the index-matching fluid to reflect light, a solution that Agilent says is simple, proven and inexpensive to manufacture.

Jennifer Pigg, executive vice president at The Yankee Group, says MEMS shows promise because the mirrors can adjust microscopically in three dimensions. "With any luck, you can go diagonally," Pigg says, increasing the number of possible gates and enabling faster provisioning and fault recovery by creating a fully redundant switch fabric with far fewer ports. "It really does look like the future," she says. "It saves a huge amount of money."

The Yankee Group predicts MEMS technology will account for 65 percent of the all-optical switch market. Bubble technology such as Agilents will capture 20 percent of the market, with the remaining 15 percent divided among other technologies. The firm predicts the all-optical switch market will grow from a standing start in 2000 to more than $2 billion by 2005.

"The name of the game is to help carriers reduce the cost of providing bandwidth," Lucents Austin says.

While The Yankee Group predicts the lions share of the all-optical market will go to MEMS and bubble technologies, theres still room for alternative approaches. Start-up companies with interesting angles on the all-optical switch problem have been popping up like mushrooms. Among them are:

  • Light Management Group, a Burlington, Ontario, company that in December demonstrated its fiber-optical line switch. The switch is small, does not have any mechanical parts and uses an "acousto-optical deflector set" to randomly connect the channels from the array to a single fiber line.
  • Chorum Technologies, a Richardson, Texas, maker of all-optical processors and subsystems, uses liquid crystals instead of hard contacts to manipulate optical signals in its PolarWave family of products. Chorum recently acquired liquid-crystal display specialist Polytronix to help build out its line of filters, switches and processors.
  • Trellis Photonics, in Columbia, Md., has developed a solid-state technology that relies on wavelength-specific holograms written in potassium lithium tantalate niobate crystals. By building crystals into a matrix of rows and columns, any wavelength can be routed to any fiber.

The Yankee Groups Pigg also sees telecommunications potential in research at Harvard University, where scientists used chilled gases to slow, then stop, the passage of light. Two independent research teams managed light by beaming it through a chamber of gas, first slowing the light, then holding it at a standstill. The researchers revived the beam with a second flash of light, duplicating the shape, intensity and other properties of the original beam.

"Weve been able to hold it there and just let it go, and what comes out is the same as what we sent in," Ronald Walsworth, one of the researchers at the Harvard-Smithsonian Center for Astrophysics, told The New York Times.