Squeezing Light for Nanophotonic Circuits

The multiplexer device with one input and two outputs. (Source: IBS)

The multiplexer device with one input and two outputs. (Source: IBS)

The computers of the future could work almost at the speed of light. Nano­photonics could indeed bring the speed of our tech­nology to a completely different level. The Center for Inte­grated Nano­structure Physics CINAP within theInstitute for Basic Science have developed three key components of a circuit that works with light. These devices combine the advan­tages of photonics and elec­tronics on the same platform.

While we are slowing approaching the end point of Moore’s Law, the future of big data proces­sing requires high per­formance computers with higher speed opera­tions. Researchers reckon that if we build computers that process infor­mation through light, instead of electrons, computers will be able to work faster. However, at nano­meter dimensions, the wave­length of light is larger than the diameter of the silicon fiber and for this reason some light can be lost. A solution to control the propa­gation of light in matter can come from surface plasmons. These electro­magnetic waves propa­gate along the surface of some conductive materials like silver, gold, aluminum and copper. Using surface plasmons, optical infor­mation can be transmitted nearly at the speed of light and in extremely miniature volumes.

Using surface plasmons in silver nano­wires and 2D semi­conductors like molyb­denum disul­phide (MoS2), IBS scientists built three key components for optical communi­cation: optical tran­sistors, optical multi­plexers and optical signal detectors. These devices work thanks to plasmon-exciton-plasmon inter­conversion. 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 realized 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) 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 approach arises from the exciton-plasmon inter­conversion. We reported before about 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 Hyun Seok Lee. (Source: IBS)

Reference: H. S. Lee et al.: Reconfigurable exciton-plasmon interconversion for nanophotonic circuits, Nat. Comms. 7, 13663 (2016); DOI: 10.1038/ncomms13663

Link: Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science (IBS), Suwon, Korea

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