Plasmonics is a promising emerging technology that attempts to put together the best of two worlds — optics and electronics — to achieve faster computation and communication by making optical devices significantly smaller. In recent research, a team of European scientists has solved a long-standing problem in this field by sending signals over a long distance in a breakthrough that brings this technology much closer to mass production.

When compared to other technologies, electronics is relatively slow — because of physical limits in the cables, it can't be pushed over a few tens of GHz — but allows us to manipulate signals with very small devices for a cheap price; optics, on the other hand, can reach incredibly high speeds, making it a great choice for fast communications, but is relatively bulky and expensive.

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Researchers have long realized that using light for manipulating information rather than just communication could be the key to achieving much faster data processing. Unfortunately, the size and performance of photonic devices is limited by the width of optical fibers, which must be at least half of the light's wavelength in order to propagate correctly, making miniaturization efforts extremely challenging.

Often referred to as "light on a wire," plasmonics is an alternative approach to faster data processing that uses the density waves of electrons to send both optical and electronic signals on the same metal circuitry. These waves, or "plasmons", are created when light hits a metal surface under precise circumstances and have frequencies in the optical range, meaning they can encode roughly the same amount of information as fiber optics.

What's even more interesting, plasmons are not subject to the same physical constraints of light, meaning they can travel on tiny metal wires allowing the same kind of miniaturization that the electronics industry has been experiencing for decades.

A serious obstacle to the widespread use of this technology so far has been that plasmons tend to dissipate after only a few millimeters of propagation, making them unusable on most computer chips. Under the EU-funded Plasmacon project, a team of European researchers has reported they have now overcome this obstacle, demonstrating the first commercially-viable plasmonics devices.

The researchers' approach was to develop a so-called "dielectric-loaded surface plasmon polariton waveguide" (DLSPPW), a layer of dielectric that was patterned onto a gold film with a glass substrate. Using this structure, they were able to achieve waveguides only 500 nanometers in size and extend the signal propagation, opening the way to further advances.

Unlike previous results obtained by other research groups, the technology developed by the team can create plasmonic devices using existing and low-cost commercial lithography techniques, and while some issues still need to be tackled, it would seem that one of the main obstacles has just been overcome.

Using the special waveguide they developed, the researchers built several plasmonic devices including a waveguide ring resonator — a crucial component of the multiplexers in optical networks that combine and separate several streams of data into a single signal and vice versa — at much smaller sizes than usual. For instance, while current optical ring resonators have a radius of up to 300 micrometers, the one built by the team measured just five micrometers.

"I think that we will start to see this technology make its way into commercial applications over the next five to ten years," Prof Zayats, optics professor at Queen's University, Belfast, explained. "The ultimate goal is an integrated photonic circuit based on plasmonic excitations capable of performing all operations completely optically."

Research in plasmonics has quickly picked up pace and the interest of the electronics industry, including NEC and Panasonic, and the French chipmaker Silios Technology is already working on a commercialization plan that might involve either producing plasmonic components or licensing the Plasmocom technique to third parties.

The project is a collaboration between Queen's University, Aalborg University in Denmark, the University of Southern Denmark in Odense and the University of Burgundy in France.

Via ICT Results

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