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MIT makes all-optical silicon chips possible

Posted: 28 Nov 2011     Print Version  Bookmark and Share

Keywords:photonic chips  silicon  optical  garnet 

MIT researchers believe they 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 communication systems, data travels via light beams transmitted through optical fibres. 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', said 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 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 explained, because without such a device stray reflections could destabilise 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.

Photonic chips

MIT produces component to allow complete optical circuits on silicon chips.

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