Nanowire networks route light
Technology Research News
chips that use light rather than electricity to dramatically speed computing
are probably a long way off, but research efforts aimed at producing nanoscale
optics could make chip-scale communications devices and scientific equipment
practical within a decade.
An increasing amount of this research effort is focused on using
photonic crystal chips to channel light, but photonic crystal channels are
generally larger than a thousandth of a millimeter, or 1,000 nanometers.
Another approach is to use nanowires to guide lightwaves.
Researchers from the University of California at Berkeley, the Lawrence
Berkeley National Laboratory and the National Aeronautics and Space Administration
(NASA) have devised nanoscale optical networks made from nanoscale wires
and ribbons and have routed light signals through the networks. They have
also used nanoribbons to guide light into microscopic droplets as a way
of identifying molecules.
The proof-of-concept work could lead to electronic computer chips
that sport high-speed optical links, miniaturized communications devices,
and chip-scale scientific and medical spectroscopy. Practical applications
include on-chip information processing that uses photons to represent information,
and chemical and biological sensing devices that could be integrated into
biochips, said Peidong Yang, an associate professor of chemistry at the
University of California at Berkeley and faculty scientist at the Lawrence
Berkeley National Laboratory.
The researchers showed previously that nanowires and ribbons are
efficient lightwave guides. The nanowires and ribbons are narrower than
the wavelengths of light they transmit, and unlike traditional optical fiber,
some light is transmitted along the outside of the nanowires and ribbons.
The researchers expanded the work by showing that it is possible
to transmit nanosecond light pulses from gallium nitride and zinc oxide
nanowire lasers through connected tin oxide nanoribbon waveguides.
They connected a 130- by 65,000-nanometer gallium nitride nanowire
to a 240- by 260- by 460,000-nanometer tin oxide nanoribbon and used a laser
to stimulate the nanowire into lasing, which sent 8-nanosecond light pulses
into the nanoribbon. About 50 percent of the light made it across the connection.
The wire and ribbon overlapped by two microns and were held together by
natural electrostatic forces. By comparison, human hair is about 75,000
The researchers also built simple nanoribbon networks that filter
white light into different colors and route the separate colors. Different
wavelengths of light can be used to send information along the same channel
at the same time, increasing the bandwidth of the channel. This is a widely-used
technique in today's communations networks.
The researchers attached three successively smaller nanoribbons
to a larger nanoribbon and transmitted white light through the larger nanoribbon.
The structure caused green light to flow into the first branch nanoribbon,
aqua light into the second, and blue into the third. When they transmitted
red light the light remained within the larger nanoribbon, while green light
flowed into the first branch nanoribbon and blue light flowed through all
The researchers also demonstrated that the nano networks are capable
of relatively complicated optical routing. They configured four nanoribbons
into a grid and routed light signals around 90 degree bends in the grid.
Though only about 5 percent of the light was transmitted at the nanoribbon
junctions, the researchers found that light pumped into the end of one nanoribbon
was transmitted to the seven other nanoribbon ends, showing that some of
the light made it through a pair of 90 degree turns.
The researchers also showed that the nanowires and ribbons are capable
of sensing molecules.
They inserted a nanoribbon into a 3-picoliter dye-containing droplet
and sent blue light through the nanoribbon. This caused the dye to fluoresce,
and some of the fluorescent light traveled back through the nanoribbon.
They were able to determine the substance that emitted the light by spectroscopy
-- analyzing the mix of lightwaves in the fluorescent light. A picoliter
is one trillionth of a liter, or about one 20,000th of a drop of water.
They also placed a 1-picoliter dye-containing droplet on the middle
of a nanoribbon and transmitted white light through the ribbon. The dye
absorbed a color of light that indicated the substance that makes that makes
up the dye. Measuring the spectrum of the light at the end of the nanoribbon
shows the missing color.
These spectroscopy techniques demonstrate that nanoribbons could
be used in biochips for sensing chemicals and biological molecules, according
Making nanowire and ribbon waveguides practical requires methods
of manufacturing the devices in parallel, said Yang. The significant bottleneck
to making the devices practical is developing parallel processes for integrating,
or constructing them, he said. Although the integration process used in
the current work is serial, hence slow and inefficient, it "represents the
first step towards integrating nanowire-based photonic elements [into chips],"
Networks of nanowires and ribbons that carry out optical routing
and nanowire and ribbon spectroscopy devices could be used practically in
five to ten years, said Yang.
Yang's research colleagues were Donald J. Sirbuly and Matt Law of
the University of California at Berkeley and Lawrence Berkeley National
Laboratory, Peter Pauzauskie, Haoquan Yan, Kelly Knutsen and Richard J.
Saykally of the University of California at Berkeley, and Alex V. Maslov
and Cun-Zheng Ning of NASA. They published the research in the May 20, 2005
issue of the Proceedings of the National Academy Of Sciences. The
research was funded by the Department of Energy, the Camille and Henry Dreyfus
Foundation and the Beckman Foundation.
Timeline: 5-10 years
Funding: Government, Private
TRN Categories: Optical Computing, Optoelectronics and Photonics;
Nanotechnology; Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Optical Routing and Sensing
with Nanowire Assemblies," Proceedings of the National Academy of Sciences,
May 20, 2005
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