Opto-Electronics


Plasmonic device holds promise for super-fast computing

14 October 2015 Opto-Electronics Electronics Technology

In a promising discovery towards the realisation of high-speed optical computing, researchers from Duke University’s Pratt School of Engineering have developed an ultrafast light-emitting device that can flip on and off 90 billion times a second.

A nanoscale view of the new superfast fluorescent system using a transmission electron microscope. The silver cube is just 75 nm wide. The quantum dots (red) are sandwiched between the silver cube and a thin gold foil.
A nanoscale view of the new superfast fluorescent system using a transmission electron microscope. The silver cube is just 75 nm wide. The quantum dots (red) are sandwiched between the silver cube and a thin gold foil.

Although lasers can switch this fast, they are too energy-hungry and unwieldy to integrate into computer chips. This new research has taken a different approach, by pushing semiconductor quantum dots to emit light at more than 90 GHz. This so-called plasmonic device could one day be used in optical computing chips or for optical communication between traditional electronic microchips.

The new speed record was set using plasmonics. When a laser shines on the surface of a silver cube just 75 nanometres wide, the free electrons on its surface begin to oscillate together in a wave. These oscillations create their own light, which reacts again with the free electrons. Energy trapped on the surface of the nanocube in this fashion is called a plasmon.

An illustration showing the silver nanocube sitting on top of a thin gold foil, with red quantum dots sandwiched between.
An illustration showing the silver nanocube sitting on top of a thin gold foil, with red quantum dots sandwiched between.

The plasmon creates an intense electromagnetic field between the silver nanocube and a thin sheet of gold placed a mere 20 atoms away. This field interacts with quantum dots – spheres of semiconducting material just 6 nm wide – that are sandwiched in between the nanocube and the gold. The quantum dots, in turn, produce a directional, efficient emission of photons that can be turned on and off at more than 90 GHz.

The group is now working to use the plasmonic structure to create a single photon source – a necessity for extremely secure quantum communications – by sandwiching a single quantum dot in the gap between the silver nanocube and gold foil. They are also trying to precisely place and orient the quantum dots to create the fastest fluorescence rates possible.

Aside from its potential technological impacts, the research demonstrates that well-known materials need not be limited by their intrinsic properties.





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