New optical device for faster, cooler computers

Scientists have developed a new "groundbreaking" optical device that may lead to more powerful computers that run faster and are cooler.
The optical device could enhance optical information processing in computers.
In an optical diode, the light input in one direction is transmitted while the light input in the opposite direction is blocked.
The new optical diode, designed by Lan Yang and her collaborators from Washington University in St Louis, is made from parity-time (PT) symmetric micro-resonators in which loss of one of the resonators is balanced by the gain in the other.
Breaking the PT-symmetry, by tuning the coupling strength between the resonators, leads to strong field localisation and hence enables nonlinearity-based one-way transmission for light.

Yang's group created the optical diode by coupling tiny doughnut shaped optical resonators - one with gain and the other with loss - on a silicon chip.

"This diode is capable of completely eliminating light transmission in one direction and greatly enhancing light transmission in the other nonreciprocal light transmission," said Bo Peng, a graduate student in Yang's group and the paper's lead author.
An electrical diode prevents electricity from back-flow along a wire providing protection to crucial parts of an electronic circuit or processor; an optical diode does the same thing with light.
"We believe that our discovery will benefit many other fields involving electronics, acoustics, plasmonics and meta-materials," Yang said.

"Coupling of so-called loss and gain devices using PT (parity-time)-symmetry could enable such advances as cloaking devices, stronger lasers that need less input power, and perhaps detectors that could 'see' a single atom," said Yang.
Applying the principles of PT symmetry leads optics to a completely different set of behaviours not predicted by conventional physics with only loss or only gain.
To make their optical diode, Sahin Kaya Ozdemir, research scientist in Yang's group, and Peng used two micro-resonators positioned so that light can flow from one to the other.
"Our resonators are small enough to use in computers and future optical information processors. At present, we built our optical diodes from silica, which has very little material loss at the telecommunication wavelength. The concept can be extended to resonators made from other materials to enable easy CMOS compatibility," Peng said.

The research appears in the journal Nature Physics.