Scientists have broken new ground in the quest to construct the first light based computer. A group of researchers from the Washington University of St. Louis (WUSTL) have managed to create the first optical diode.

In theory, an optical diode performs a very simple task. Photons coming into the input of the diode will enter the device and is transmitted to the output section of the diode. However, any photons coming in from the opposite direction will be blocked. This means that optical diodes allow a one-way transmission of light. However, making it work in the real world is not as simple as it seems.

To create their optical diode, the WUSTL team led by associate professor and systems engineering Lan Yang used a principle similar to what can be observed in the Whispering Gallery in the St. Paul's Cathedral in London. In this part of the cathedral's dome, sound emitted from one part of the dome is transmitted to the opposite side due to the sound waves traveling across the dome's curved surface. The team published its findings in the online journal Nature Physics.

"This diode is capable of completely eliminating light transmission in one direction and greatly enhancing light transmission in the other nonreciprocal light transmission," said WUSTL graduate student Bo Peng. Peng is also the lead author of the paper.

The researchers designed the optical diode with two minute doughnut shaped optical resonators coupled together and mounted on a silicon chip. One of the resonators has a gain while the other has a loss, which allows for non-linear transmission of light. This non-linear transmission is similar to the effect seen in the Whispering Gallery in London.

"We believe that our discovery will benefit many other fields involving electronics, acoustics, plasmonics and meta-materials," said Yang. "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."

In a normal electric diode, electricity is transmitted only in one direction and any backflow is blocked by the diode. This protects sensitive electronic circuitry from damage. In terms of principle alone, the optical diode plays a similar role. However, light is used in lieu of electricity.

"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." said Peng.

The new diode has potential applications in optical computing. There are a number of key advantages to using light as a medium for computing over electricity. First of all, the use of photons offers higher bandwidth compared to electrons. Moreover, optical computers are also theorized to allow for higher performance ratings compared to conventional computers.

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