Korean team squeezes light into miniature devices

29th November 2016
Plasmon-exciton-plasmon interconversion used in optical circuits made of silver nanowires and 2D semiconductors

Scientists at the Institute for Basic Science (IBS) in Korea have developed optical transistors, optical multiplexers and optical signal detectors using silver nanowires and 2D semiconductors including MoS2.

Published in Nature Communications, the devices used a phenomenon called plasmon-exciton-plasmon interconversion to combine the advantages of photonics and electronics on the same platform.

Surface plasmons are electromagnetic waves that propagate along the surface of s conductive materials like silver, gold, aluminum and copper. They are of growing interest as they allow optical information to be transmitted nearly at the speed of light and in extremely small spaces.

IBS scientists constructed the optical transistor by interconnecting the silver nanowire to a flake of MoS2. Light shone on the device is converted to surface plasmon, than to exciton, back to surface plasmon and eventually emitted as light with a shorter wavelength compared to the initial input. For example, if the input light is green, the output light can be red.

Wavelength multiplexing devices were realised in a similar way, but instead of having only a flake of MoS2, the researchers used an array of three different 2D semiconductor materials emitting light at different wavelengths. In this structure, for example, a single input light (violet color) generates three output lights (blue, green and red).

The propagating optical signals along the silver nanowire can be also transformed and detected as electrical signals by an optical signal detector.

"The originality of this paper arises from the exciton-plasmon interconversion. We published before the conversion of exciton to plasmon, and from plasmon to exciton using silver nanowire/2D semiconductor hybrids, but this is the first time that we can complete the circle going from plasmons to excitons and back to plasmons. Using this concept, we created optical transistors and multiplexers," explains professor Hyun Seok Lee, first author of this study.

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