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LBNL researchers have demonstrated that semiconductor “nanoribbons”
can be used as "waveguides" for channeling and directing the
movement of light through circuitry. This research, which was performed
with single crystals of tin oxide measuring up to 1.5 mm in length, but
only a few hundred or fewer nanometers in width and thickness, is an important
step towards realizing the promise of extremely high speed photonic technology.
In photonic technology, the use of electrons moving through semiconductors
as information carriers is replaced with the movement of light waves or
photons. Whereas electrons must carry information sequentially, one electron
at a time, in photonics there is no limit to the number of information packets
that can be transmitted simultaneously. Hints of the potential of photonics
can be glimpsed in today's fiber-optic communications, in which a single
optical fiber can carry the equivalent of 300,000 telephone calls at the
same time. However, the power of fully realized photonics goes far beyond
this. For example, it has been estimated that a photonic internet could
transmit data at 160 gigabits per second, thousands of times faster than
today's typical high-speed connection. Another possibility is the optical
computer, which could solve problems in seconds that would take today's
electronic computers months or even years to solve.
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For the promise of photonics to be delivered, however, scientists must
first find a way to manipulate and route photons with the same dexterity
now available for manipulating and routing electrons. Complicating the
problem is the fact that electrons tend to stay in the wires used to route
them, but photons require specially designed “waveguides”
to keep them on course. Developing these on the scale of modern IC circuitry
has been challenging.
The LBNL team investigated the use of chemically synthesized nanowires
and nanoribbons as optical waveguides. The single crystalline tin oxide
(SnO2) nanoribbons they produced were rectangular in cross section and
measured about 1.5 mm in length and between 100 to 400 nanometers in width
and thickness. They then performed a series of experiments that demonstrated
the usefulness of these nanoribbons in controlling visible light. In a
first test, nanowire lasers and optical detectors were attached to opposite
ends of their tin oxide nanoribbons to demonstrate that light could be
propagated and modulated through optical cavities in the nanoribbon, which
have dimensions smaller then the wavelength of the light. The nanoribbons
were long and strong enough to be formed into tight S-turns and twisted
into a variety of shapes without compromising their transmission characteristics.
The team also found that nanoribbon waveguides could be coupled together
to create optical networks that could serve as the basis of miniaturized
photonic circuitry. The most efficient light transfer between ribbons
was achieved in a staggered side-by-side arrangement, in which two ribbons
interact over a distance of several micrometers.
Nanoribbon waveguides are the newest addition to the growing photonics
"toolbox" which also includes nanoscale lasers and photodetectors.
The ultimate goal is to integrate these individual components together
into a photonic system-on-a-chip, so that photonic operations, including
light emission, routing, and detection, can be done on a much smaller
scale.
P. Yang,
(510) 643-1545, Materials Sciences Division (510 486-4755), Berkeley Lab.
Matt Law, Donald J. Sirbuly, Justin C. Johnson, Josh Goldberger, Richard
J. Saykall, and Peidong Yang “Nanoribbon waveguides for subwavelength
photonics integration," Science, 27 August 2004.
Additional support from the Camille and Henry Dreyfus Foundation, the
Alfred P. Sloan Foundation, the Beckman Foundation, and a National Science
Foundation Graduate Research fellowship to J.E. Goldberger.
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