• Caroline Ross, the Toyota Professor of Materials Science and Engineering at MIT

    Photo: Allegra Boverman

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Important step toward computing with light

Research at MIT produces long-sought component to allow complete optical circuits on silicon chips.


There has been enormous progress in recent years toward the development of photonic chips — devices that use light beams instead of electrons to carry out their computational tasks. Now, researchers at MIT have filled in a crucial piece of the puzzle that could enable the creation of photonic chips on the standard silicon material that forms the basis for most of today’s electronics.

In many of today’s communication systems, data travels via light beams transmitted through optical fibers. Once the optical signal arrives at its destination, it is converted to electronic form, processed through electronic circuits and then converted back to light using a laser. The new device could eliminate those extra electronic-conversion steps, allowing the light signal to be processed directly.

The new component is a “diode for light,” says Caroline Ross, the Toyota Professor of Materials Science and Engineering at MIT, who is co-author of a paper reporting the new device that was published online Nov. 13 in the journal Nature Photonics. It is analogous to an electronic diode, a device that allows an electric current to flow in one direction but blocks it from going the other way; in this case, it creates a one-way street for light, rather than electricity.

This is essential, Ross explains, because without such a device stray reflections could destabilize the lasers used to produce the optical signals and reduce the efficiency of the transmission. Currently, a discrete device called an isolator is used to perform this function, but the new system would allow this function to be part of the same chip that carries out other signal-processing tasks.

To develop the device, the researchers had to find a material that is both transparent and magnetic — two characteristics that rarely occur together. They ended up using a form of a material called garnet, which is normally difficult to grow on the silicon wafers used for microchips. Garnet is desirable because it inherently transmits light differently in one direction than in another: It has a different index of refraction — the bending of light as it enters the material — depending on the direction of the beam.

The researchers were able to deposit a thin film of garnet to cover one half of a loop connected to a light-transmitting channel on the chip. The result was that light traveling through the chip in one direction passes freely, while a beam going the other way gets diverted into the loop.

The whole system could be made using standard microchip manufacturing machinery, Ross says. “It simplifies making an all-optical chip,” she says. The design of the circuit can be produced “just like an integrated-circuit person can design a whole microprocessor. Now, you can do an integrated optical circuit.”

That could make it much easier to commercialize than a system based on different materials, Ross says. “A silicon platform is what you want to use,” she says, because “there’s a huge infrastructure for silicon processing. Everyone knows how to process silicon. That means they can set about developing the chip without having to worry about new fabrication techniques.”

This technology could greatly boost the speed of data-transmission systems, for two reasons: First, light travels much faster than electrons. Second, while wires can only carry a single electronic data stream, optical computing enables multiple beams of light, carrying separate streams of data, to pass through a single optical fiber or circuit without interference. “This may be the next generation in terms of speed” for communications systems, Ross says.

Ross’ colleagues in the research included Lionel Kimerling, the Thomas Lord Professor of Materials Science and Engineering, and former students Lei Bi ’11 and Juejun Hu PhD ’09. The work was funded by the National Science Foundation and an Intel fellowship for Bi.

“This is a big advance in optical communications,” says Bethanie Stadler, a professor of electrical and computer engineering at the University of Minnesota, who was not involved in this research. The work is “significant,” she says, “as the first device with garnet integrated onto [silicon] devices.”


Topics: Computer chips, Computer science and technology, Computing, Electrical engineering and electronics, Innovation and Entrepreneurship (I&E), Materials science, Optical computing, Optical flow switching, Photonics

Comments

great, and, it mentions an all optic computer... When will be able to put our hands on a all optical PC, at current prices we have?
Great research. Dr.A.Jagadeesh Nellore(AP),India
This research would probably inspire to make a fully light i.e 'photonic power distribution and transmission system' instead of electrical power ,thereby reducing transmission losses and dangers involved with electricity
What will be interesting about all optical computing is that it will be immune to high voltage environments that will be used in levitating devices.
Didn't IBM make a similar announcement last year about this same time? I believe researchers Yurii Vlasov, William Green and Solomon Assefa announced last year that they had incorporated nano photonics and electrical circuitry all on the same silicon chip. Maybe this is better, or solves some of the problems that they were having, but it seems very similar.
"First, light travels much faster than electrons" Doesn't sound accurate to me. Electrons technically travel at the speed of light. I believe it is the digital encoding/decoding and lack of multiplexing over electric wire that makes it slower. Am I missing something?
The actual speed of electrons isn't really the issue slowing electric circuits even though the resistance of the media is a big limiter. Electrical signals can suffer interference from other electrical signals i.e. RFI and EFI. Light travels through what is basically a tunnel where other light (interference) cannot get to it. This almost removes the need to resend data and reduces the need for message reception verification, cutting down again on processing time. And yes being able to transmit multiple signals at the same time without interference is a huge advantage.
We seem to forget that light in any form is frequency. each componet in acircuit has a frequency going in and a seperate frequency comming out. optical plastic can be tuned to produice that frequency and replace each componet.
As far as I remember from physics classes: The electrons themselves (depending on the type of matter theyre in, its diameter and the voltage) travel in some wires with a speed comparable to us walking. What actually matters, and is experienced, is the speed at which the electric field is propagated through space along the wire. Thats probably close to the speed of light. Similarly as with water in a long, filled pipe, when you open the valve. The molecules being at the valve take a long time arriving, but water comes almost immidiately out of the other end, because the ones behind press them. Like a row of dominos. The above is more a question, than a statement. Could someone clarify please.
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