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90GHz nanopatch plasmonic antennas surpass lasers

Posted: 29 Jul 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Duke University? antenna? laser? plasmon?

Much research has been done to integrate lasers on silicon chips for optical computing. This time, nanopatch plasmonic antennas (NPAs) are used for emission of telecommunications infrared signals at speeds up to 90GHz and could terahertz speeds in the future.

"We want to speed-up in emission rate to build an ultrafast and super-bright light emitting diode," said Duke University assistant professor Maiken Mikkelsen. "This will involve using conducting materials to bring electrical current to the quantum dots to create enhanced emission from same plasmonic structure. Such a device has the potential to operate at very low power levels, at a few attojoules, which is critical to transform future information processing and communications, currently limited by heat dissipation," said Mikkelsen.

The whole semiconductor industry has been trying to convert from electrons to photons as the signal medium for computing on silicon chips. Every kind of silicon photonic devices have been demonstrated, except the emitters. Unfortunately, lasers, the standard communications emitter, are incompatible with silicon, though a thousand methods are being researched to solve that problem. Now Duke University electrical engineers say forget lasers, but instead use their NPAs coupled to quantum dots to communicate 90GHz and up on-chip or between them at a radiative quantum efficiency of over 50 per cent.

Nanopatch plasmonic antenna

Artists rendering of a nanopatch plasmonic antenna (NPA, silver cube) sitting atop a gold substrate (gold) separated from it by a polymer (not shown) containing colloidal quantum dots (QD, red). (Source: Duke University)

"Typical emitters such as molecules, quantum dots and semiconductor quantum wells have slow spontaneous emission with lifetimes of 1ns to 10ns, creating a mismatch with high-speed nanoscale optoelectronic devices such as LEDs, single-photon sources and lasers. Here we experimentally demonstrate an ultrafast (To achieve their high-speed switching rate, the researchers use plasmons (free electrons on a surface that oscillate together in a wave) as nano-antennas consisting of silver nanocubes coupled to a thin gold film (20 atoms thin) separated from the substrate by a thin polymer spacer layer with a colloidal core of shell quantum dots. This structure increases the spontaneous emission rate by 880-times while simultaneously enhancing the fluorescence intensity by 2300-times while maintaining a high efficiency.

NPAs coupled to quantum dots

Postdoctoral researches Gleb Akselrod (left) and Thang Hoang (right) inspect their nanopatch plasmonic antennas (NPAs) coupled to quantum dots in Maiken Mikkelsen's (centre) laboratory. (Source: Duke University)

"We have demonstrated an ultrafast spontaneous emission source with an emission speed exceeding 11ps from a hybrid system consisting of plasmonic nano-antennas coupled to ensembles of colloidal quantum dots," stated Mikkelsen and colleagues.

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