MIT takes big step towards optical computing

MIT researchers say they’ve filled in the missing link required  for the creation of complete optical circuits on silicon chips.

They say their new ‘diode for light’ could enable the creation of photonic chips on the standard silicon used in most of today’s electronics.

Comparable to an electronic diode, it allows light to flow in one direction, but blocks it from going the other way. This means stray reflections can’t destabilize the lasers used to produce the optical signals and reduce the efficiency of the transmission.

While a separate device called an isolator is currently used to do this, the new system would allow this function to be part of the same chip that carries out other signal-processing tasks.

The material on which the device is based is a form of garnet, normally hard to grow on the silicon wafers used for microchips. Garnet inherently transmits light differently in one direction to another, with a different index of refraction 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, says professor Caroline Ross.

“It simplifies making an all-optical chip,” she says.

“A silicon platform is what you want to use, 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.”