Light for Faster Computer Chips

Carbon nanotube above a photonic crystal waveguide with electrodes. The structure converts electric signals into light. (Photo: WWU)

Carbon nanotube above a photonic crystal waveguide with electrodes. The structure converts electric signals into light. (Photo: WWU)

Worldwide growing data volumes make conven­tional elec­tronic processing reach its limits. Future information technology is therefore expected to use light as a medium for quick data trans­mission also within computer chips. Researchers under the direction of KIT have now demonstrated that carbon nanotubes are suited for use as on-chip light source for tomorrow’s information technology, when nano­structured waveguides are applied to obtain the desired light properties.

On the large scale, data trans­mission by light has long become a matter of routine: Glass fiber cables as light waveguides transmit telephone and internet signals, for instance. For using the advantages of light, i.e. speed and energy efficiency, also on the small scale of computer chips, researchers of KIT have made an important step from fundamental research towards application. By the inte­gration of smallest carbon nanotubes into a nano­structured waveguide, they have developed a compact minia­turized switching element that converts electric signals into clearly defined optical signals.

“The nanostructures act like a photonic crystal and allow for customizing the properties of light from the carbon nanotube,” Felix Pyatkov and Valentin Fütterling explain. “In this way, we can generate narrow-band light in the desired color on the chip.” Processing of the waveguide precisely defines the wavelength at which the light is transmitted. By engravings using electron beam litho­graphy, the waveguides of several micrometers in length are provided with finest cavities of a few nanometers in size. They determine the waveguide’s optical properties. The resulting photonic crystals reflect the light in certain colors, a phenomenon observed in nature on apparently colorful butterfly wings.

As novel light sources, carbon nanotubes of about 1 micrometer in length and 1 nanometer in diameter are positioned on metal contacts in transverse direction to the waveguide. At KIT, a process was developed, by means of which the nanotubes can be integrated speci­fically into highly complex structures. The researchers applied the method of dielectro­phoresis for deposition of carbon nanotubes from the solution and their arrangement vertically to the waveguide. This way of separating particles using inhomo­geneous electric fields was originally used in biology and is highly suited to deposit nanoscaled objects on carrier materials. The carbon nanotubes integrated into the waveguide act as a small light source. When electric voltage is applied, they produce photons.

The compact electricity/light signal converter presented now meets the requirements of the next generation of computers that combine electronic components with nano­photonic waveguides. The signal converter bundles the light about as strongly as a laser and responds to variable signals with high speed. Already now, the opto­electronic components developed by the researchers can be used to produce light signals in the gigahertz frequency range from electric signals. (Source: KIT)

Reference: F. Pyatkov et al.: Cavity-enhanced light emission from electrically driven carbon nanotubes, Nat. Phot. online 

Link: Charge transport and light-matter interaction in carbon nano systems (R. Krupke), Institute of Nanotechnology, Karlsruhe Institute of Technology, Germany

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