MIT has made a silicon-compatible 'diode for light', for all-optical chips.
"To develop the device, the researchers had to find a material that is both transparent and magnetic, two characteristics that rarely occur together," said MIT. "They ended up using a form of a material called garnet, which is normally difficult to grow on silicon wafers."
According to the university, garnet inherently exhibits different refractive indices depending on the direction with which a beam passes through it.
The researchers deposited a thin film of garnet over one half of an optical waveguide on the chip.
"The result was that light travelling through the chip in one direction passes freely, while a beam going the other way gets diverted into the loop," said MIT.
Up to 19.5dB isolation ratio is claimed for the 290µm device "near the 1,550nm wavelength" said Nature about the paper: 'On-chip optical isolation in monolithically integrated non-reciprocal optical resonators'.
The whole system could be made using standard microchip manufacturing machinery, said Professor Caroline Ross: "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."