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Nanowire waveguides come of age

31 Aug 2004

US researchers unveil nanowire waveguides in the current issue of Science.

While nanowire devices that can emit light and detect photons are already available, nanowire waveguides have so far proved elusive. Now, scientists at the University of California, Berkeley, and Lawrence Berkeley National Laboratory, both in the US, have used nanoribbons of crystalline oxide to channel light between devices.

"In the past couple of years we have demonstrated nanoscale lasers and detectors: what is missing is an element that could link these individual components together," Peidong Yang of the University of California, Berkeley, and Lawrence Berkeley National Laboratory told nanotechweb.org. "A sub-wavelength optical waveguide is exactly [what's] needed for this purpose. So we tested these ultralong nanowires as a possible candidate - it turns out that they can serve as a very good optical waveguide with low optical loss."

Yang and colleagues used nanoribbons of crystalline SnO2 as waveguides. The nanoribbons were up to 1500 µm long and rectangular in cross-section, ranging in size from 15 x 5 nm to 2 x 1 µm. According to the scientists, many of the ribbons were 100-400 nm wide and thick, which is an optimal size range for efficient steering of visible and ultraviolet light within a subwavelength cavity.

As well as proving capable of channeling visible and ultraviolet light with little optical loss, the nanoribbons were also highly flexible, despite the brittleness of bulk SnO2. That enabled relatively easy manipulation, optical linking and assembly.

The researchers injected light into a nanoribbon cavity from an optically pumped zinc oxide nanowire, and also used a zinc oxide nanowire to electrically detect photoluminescence from a nanoribbon.

"We are mostly interested in integrating these waveguide components into a fully functional photonic circuit to carry out on-chip optical computing or in applications such as chip-based chemical/biological detection," said Yang.

Next the team plans to work on integrating such nanowire components. "We are now pretty good at making such nanostructures to perform individual optical or electrical functionality," explained Yang. "But we are at an early stage in terms of a fully functional system using nanowire building blocks. This is the direction that requires much more effort."

Liz Kalaugher is editor of nanotechweb.org.

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