[Editors] MIT 'optics on a chip' may revolutionize telecom, computing,

[Elizabeth Thomson]

MIT News Office
Massachusetts Institute of Technology
Room 11-400
77 Massachusetts Avenue
Cambridge, MA  02139-4307
Phone: 617-253-2700
http://web.mit.edu/newsoffice/www

======================================
MIT 'optics on a chip' may revolutionize telecom, computing

--Research integrates photonic circuitry on a silicon chip

======================================

For Immediate Release
MONDAY, FEB. 5, 2007
Contact: Elizabeth A. Thomson, MIT News Office
Phone: 617-258-5402
Email: thomson at mit.edu

PHOTOS, GRAPHIC AVAILABLE

CAMBRIDGE, Mass.--In work that could lead to completely new devices, 
systems and applications in computing and telecommunications, MIT 
researchers are bringing the long-sought goal of "optics on a chip" 
one step closer to market.

In the January 2007 inaugural issue of the journal Nature Photonics, 
the team reports a novel way to integrate photonic circuitry on a 
silicon chip. Adding the power and speed of light waves to 
traditional electronics could achieve system performance 
inconceivable by electronic means alone.

The MIT invention will enable such integrated devices to be 
mass-manufactured for the first time. And, depending on the growth of 
the telecom industry, the new devices could be in demand within five 
years, said co-author Erich P. Ippen, the Elihu Thomson Professor of 
Electrical Engineering and Physics.

The new technology will also enable supercomputers on a chip with 
unique high-speed capabilities for signal processing, spectroscopy 
and remote testing, among other fields.

"This breakthrough allows inter- and intra-chip communications 
networks that solve the wiring problems of today's computer chips and 
computer architectures," said Franz X. Kaertner, a professor of 
electrical engineering and computer science.

In addition to Ippen and Kaertner, other members of the MIT team are 
Tymon Barwicz (PhD 2005), Michael Watts (PhD 2005), graduate students 
Milos Popovic and Peter Rakich, and Henry I. Smith, professor of 
electrical engineering and co-director of MIT's Nanostructures 
Laboratory.

Molding light waves

Microphotonics technology aims to "mold" the flow of light. By using 
two different materials that refract light differently, such as 
silicon and its oxides, photons can be trapped within a miniscule 
hall of mirrors, giving them unique properties.

The stumbling block has been that microphotonics devices are 
sensitive to the polarization of light.

Light waves moving through optical fibers can be arbitrarily 
vertically or horizontally polarized, and microphotonic circuits 
don't work well with that kind of random input. This has meant that 
devices used in photonic subsystems and optical communication 
networks, for instance, couldn't connect to the outside world without 
often having to be assembled piecemeal and painstakingly by hand.

Like polarizing sunglasses, which use vertical polarizers to block 
the horizontally oriented light reflected from flat surfaces such as 
roads or water, the MIT method of integrating optics on a chip 
involves separating the two orientations of polarized light waves.

Splitting the difference

The MIT researchers' innovative solution involves splitting the light 
emanating from an optic fiber into two arms-one with horizontally 
polarized beams and one with vertical beams-in an integrated, on-chip 
fashion.

Setting these two at right angles to one another, the researchers 
rotated the polarization of one of the arms, also in an integrated 
way. The beams from the two arms, now oriented the same way, then 
pass through identical sets of polarization-sensitive photonic 
structures and out the other side of the chip, where the two split 
beams are rejoined.

"These results represent a breakthrough in permitting the processing 
and switching of arbitrarily polarized input light signals in tightly 
confined and densely integrated photonic circuitry," said Ippen. The 
innovation means that optical components can be integrated onto a 
single silicon chip and mass-produced, cutting costs and boosting 
performance and complexity.

The advantage in integrating optics with silicon technology is that 
silicon fabrication technology "is already highly developed and 
promises precise and reproducible processing of densely integrated 
circuits," Kaertner said.  "The prospect of integrating the photonic 
circuitry directly on silicon electronic chips is ultimately also an 
important driver."

In addition to offering a breakthrough in polarization, the MIT chip 
also contains first-of-their-kind components in materials meeting 
telecommunications specifications.

"Our results illustrate the importance of academic research in 
nanofabrication and academia's role in breaking new pathways for the 
industry to follow," Smith said. "Creating these devices was only 
possible due to the unique nanofabrication facilities at MIT, 
enabling fabrication with extraordinary precision."

This work was supported by Pirelli Labs in Milan, Italy, and made use 
of MIT's Nanostructures Laboratory and MIT's Scanning Electron Beam 
Lithography Facility, both within the Research Laboratory of 
Electronics.

						###