A silver nanowire and a single atom-layer flake of�molybdenum�disulfide [Credit: Michael Osadciw]

Combining photonics and electronics in single circuit

A new combination of materials that efficiently guides electricity and light along the same wire could be a major step towards developing photonic integrated circuits.

Photonic devices – which use light in a similar way to electrical devices – can be much faster than electronic ones, but they are bulkier because standard components that focus light cannot be miniaturised nearly as well as electronic circuits.

Now, a team of researchers from the University of Rochester and the Swiss Federal Institute of Technology in Zurich have described a basic model circuit consisting of a silver nanowire and a single atom-layer flake of molybdenum disulfide (MoS2) that hold promise for guiding the transmission of light and maintaining the intensity of the signal in very small dimensions.

Using a laser to excite electromagnetic waves called plasmons at the surface of the wire, the researchers found that the MoS2 flake at the far end of the wire generated strong light emission and going in the other direction, as the excited electrons relaxed, they were collected by the wire and converted back into plasmons, which emitted light of the same wavelength.

“We have found that there is pronounced nanoscale light-matter interaction between plasmons and atomically thin material that can be exploited for nanophotonic integrated circuits,” said Nick Vamivakas, assistant professor of quantum optics and quantum physics at the University of Rochester and one of the authors of a paper in the journal Optica.

The key to the experiment’s success is the introduction of the MoS2 flake. In bulk MoS2, electrons and photons interact as they would in traditional semiconductors like silicon, but as MoS2 is reduced to thinner and thinner layers the transfer of energy between electrons and photons becomes more efficient.

The key to MoS2’s desirable photonic properties is in the structure of its energy band gap. MoS2 can be reduced to atomically thin layers – similar to graphene – and as the material’s layer count decreases, it transitions from an indirect to direct band gap, which allows electrons to easily move between energy bands by releasing photons.

Typically one would expect about a third of the remaining energy to be lost for every few microns the plasmons travelled along the wire, explained Kenneth Goodfellow, a graduate student at Rochester and lead author. “It was surprising to see that enough energy was left after the round-trip,” he added.

Combining electronics and photonics on the same integrated circuits could drastically improve the performance and efficiency of mobile technology and the researchers say the next step is to demonstrate their primitive circuit with light emitting diodes.

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