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The Raelian Movement
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Nano Antenna Steers Photons
A nanoscale version of a TV antenna directs light.
http://www.technologyreview.com/computing/26106/?nlid=3427&a=f
By Duncan Graham-Rowe
Tuesday, August 24, 2010
A new optical antenna could improve the efficiency of devices that
handle just a few photons at a time, such as quantum computers and
quantum cryptography circuits. The antenna, which receives and
transmits light in one direction, is a few hundred nanometers in size.
With five nanoscopic gold bars of diminishing length sitting across
one larger bar, it resembles a directional TV antenna.
Niek van Hulst, a professor at the Institute of Photonic Sciences in
Barcelona, Spain, led the development of the nano-antenna. He says it
could prove useful for quantum computing and quantum cryptography
because it can transmit light in a single direction. Currently, the
components used to emit and detect photons for these purposes do so in
all directions. "It's very difficult to control where the photons go,"
he says.
Van Hulst and colleagues took inspiration for the new device from a
type of radio antenna called a Yagi-Uda antenna. "We use exactly the
same one used to detect TV signals," he says. The length of a Yagi-Uda
antenna needs to be roughly the same as the wavelength of
electromagnetic radiation it's tuned to. For light, this is the
nanometer range.
A Yagi-Uda antenna has five parallel bars, known as elements. Only one
of these elements--the second longest, or the feed element--is
connected to a circuit. The rest are passive, constructively and
destructively interfering with the signal to make it directional.
Van Hulst and colleagues used electron beam lithography to create the
elements, depositing very small strips of gold on a glass substrate,
each with a specific length and separation. Causing the antenna to
resonate at a very high frequency--in the terahertz range--makes it
emit light at a wavelength of around 800 nanometers (infrared light).
To test the device, the team used it as a transmitter rather than a
receiver. The signal was fed to the antenna in the form of a light
signal that caused electrons in the feed element to resonate.
One major challenge was to find a way to stimulate only the feed
element. Since these gold elements are smaller than the wavelength of
light, it is not possible to focus light precisely enough to do this.
The solution was to pepper one end of the feed element with quantum
dots--nanoscopic chunks of a semiconductor material (in this case, a
colloidal cadmium selenide-based semiconductor). The size of the
quantum dots determines the wavelength of light they emit when they
are optically stimulated. When the entire structure is illuminated
with infrared light, the quantum dots are stimulated, while the
element remains unaffected. "The quantum dots lose all their energy to
the element," Van Hulst says, causing electrons within the gold to
resonate at a similar frequency and emit infrared. The rest of the
Yagi-Uda structure then comes into play, with the remaining gold
elements interfering with the emitted light, canceling it out in all
directions but one. The work was published last week in the journal
Science.
"It's the best optical antenna I have seen," says Markus Lippitz, at
the Max Planck Institute for Solid State Research, in Stuttgart,
Germany. Not only does it have the most complex structure of any
optical antenna developed so far, Lippitz says, but it is also the
first to be used to send photons.
There are other ways to redirect the light from single-photon devices,
notes Harald Giessen, a professor at the University of Stuttgart. One
way is to put quantum dots in cavities so that light can only escape
in one direction. But using nano-antennas should be more efficient
because they ensure that more photons are detected.
Lippitz says further improvements in optical antenna design research
can be expected. "Currently people are just copying from
radio-frequency schemes," he says. "The next step would be to make
them more optimized for photonics."
"Ethics" is simply a last-gasp attempt by deist conservatives and
orthodox dogmatics to keep humanity in ignorance and obscurantism,
through the well tried fermentation of fear, the fear of science and
new technologies.
There is nothing glorious about what our ancestors call history,
it is simply a succession of mistakes, intolerances and violations.
On the contrary, let us embrace Science and the new technologies
unfettered, for it is these which will liberate mankind from the
myth of god, and free us from our age old fears, from disease,
death and the sweat of labour.
Rael
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