MIT Team Details Optics-On-A-Chip Device

The Associated Press
Sunday, February 11, 2007; 5:50 PM

SAN JOSE, Calif. -- Fiber-optic networks transmit massive amounts of information quickly, but the signals weaken as the data-carrying light travels long distances. Now, researchers at the Massachusetts Institute of Technology said they've overcome a major obstacle in harnessing the full power and speed of the light waves.

It promises to solve a problem that's long plagued fiber-optic networks: Light waves gradually weaken over distances as they become polarized, or randomly oriented horizontally and vertically. The tools available to fix it are expensive to deploy on a massive scale.

The MIT researchers reported in a recent edition of the journal Nature Photonics that they've devised a solution that utilizes the mass-production capabilities of standard silicon chips.

It's a promising development as bandwidth-hungry video puts a strain on networks and consumers demand seamless transmissions.

Like polarizing sunglasses that block light waves oriented in different directions, the MIT researchers created a clever device that splits the light beams as they pass through a circuit. The device then rotates one of the polarized beams, before both beams are rejoined on their way out of the circuit, retaining the signals' strength.

But it's not just that device that the researchers are touting.

They're also trumpeting the innovative method they devised to integrate the optical circuitry with electronic circuitry on the same silicon chip.

"It's a big step forward _ no one was able to do this before in a way that is manufacturable and takes advantage of the manufacturability of silicon technology," said Erich Ippen, an MIT electrical engineering and physics professor and one of the study's co-authors.

Scientists have been chasing ways to tap into the enormous power of light waves in networks while figuring out how to manufacture the circuitry cheaply, and on a massive scale, using the established processes of the semiconductor industry.

They have often been stymied by incompatibility issues between silicon and light sources, but in recent years have major strides in discovering ways for the materials to work together.

The MIT research team demonstrated a working circuit on a chip that they said could be easily reproduced using silicon fabrication technology that is already highly developed.

Independent technology experts said the invention could eventually make its way onto next-generation telecommunications chips, and devices like it could help redefine how optical networks are built.

Connie Chang-Hasnain, a professor of electrical engineering and computer science at the University of California, Berkeley, said overcoming the problem currently requires large components that takes an operator several hours with precision instruments to assemble.

"Here, you just print (a silicon chip) and nobody is needed to align it," she said. "Imagine the massive increase in efficiency and the reduction in the need for labor and precision instruments. That's tremendous."

The advance comes as companies are looking for ways to boost the performance of their optical devices while lowering costs, as the technology becomes increasingly attractive to service providers spending heavily to upgrade their networks.

Video, which consumes thousands of times the network space of e-mail messages, is a key driver of those upgrades as Internet users demand more bandwidth to download content from sites like YouTube, and service providers prepare for the transition to Internet Protocol Television, or IPTV _ TV delivered over a broadband connection.

Alex Schoenfelder, general manager of the integrated photonics business at JDS Uniphase Corp., said the MIT research could help drive down production costs of making optical devices while moving the technology away from the core of a network and toward the end consumer.

"It will push the boundary between optics and electronics very close to the end customer," he said. "And that will be the significance _ it will open the marketplace to significantly higher volumes than we're serving today."

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