IBM Scientists Harness ``Slow Light'' for Optical Communications

As described in today's issue of the journal Nature, IBMscientists were able to slow light down to less than 1/300th of itsusual speed by directing it down a carefully designed channel ofperforated silicon called a "photonic crystal waveguide." Further, theunique design of the device allows the light's speed to be varied overa wide range simply by applying an electrical voltage to thewaveguide.

Researchers have known for some years how to slow light to a crawlunder laboratory conditions, but actively controlling the light speedon a silicon chip, using standard silicon with standard micro- andnanoelectronic fabrication technology, is a first. The device's smallsize, use of standard semiconductor materials, and ability to moreclosely control this "slow light" could make the technology useful forbuilding ultra-compact optical communications circuits that arepractical for integration into computer systems.

"This work is an example of our continued commitment to push thelimits of exploratory science," said Dr. T.C. Chen, vice president ofScience and Technology for IBM Research. "We are constantly exploringnew technologies that might enhance our systems and storage products.We believe this brings real value to both our clients, who rely onthese products to enhance their business, and to their customers, whoultimately benefit from the new and improved services they makepossible."

While chip performance has continued to increase, electronicsystems don't always reap the full benefits. Just as trafficcongestion can hinder commerce by limiting the flow of products andmaterials within a busy city, the inability to more quickly moveinformation around within electronic systems is one of the biggestbottlenecks in electronic design today. The work announced by IBMcould help relieve such constraints.

Scientists have searched for practical ways to use light to speedcommunication between the components within a computer. But, to bepractical, the components to support such an optical network will needto provide excellent control over the light signal, while also beingvery small and inexpensive to manufacture. The IBM work addressesseveral pieces of this puzzle.

The IBM team succeeded using a photonic crystal waveguide - a thinslab of silicon punctuated by regular arrays of holes that scatterlight. The pattern and size of the holes gives the material a veryhigh refractive index -- the higher the refractive index, the slowerthe light. Heating the waveguide locally with a small electricalcurrent alters the refractive index, allowing the speed of light to bequickly tuned over a large range with very low applied electric power.

The active area of the IBM device is microscopically small,indicating the possibility of complex light-based circuits withfootprints not much larger than semiconductor circuits. Themanufacturing processes used to build the device are available innearly any semiconductor factory. The capabilities demonstrated intoday's Nature article could be applied to create a variety ofnanophotonic components such as optical delay lines, optical buffers,and even optical memory, all of which would be useful in buildingcomputer systems knitted together by powerful optical communicationsnetworks.

The report on this work, "Active control of slow light on a chipwith photonic crystal waveguides" by Yurii A. Vlasov, Martin O'Boyle,Hendrik F. Hamann, and Sharee J. McNab of IBM's T.J.Watson ResearchCenter in Yorktown Heights, N.Y. is published in the November 3 issueof Nature. This work was partially supported by the Defense advancedResearch Agency (DARPA) through the Defense Sciences Office program"Slowing, Storing and Processing Light".

About IBM Research Division

IBM Research is the world's largest information technologyresearch organization, with about 3,000 scientists and engineers ineight labs in six countries. IBM has produced more researchbreakthroughs than any other company in the IT industry. For moreinformation on IBM Research, visit http://www.research.ibm.com.

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Additional information on silicon nanophotonics available at:http://www.research.ibm.com/photonics/