Another important innovation in
the manipulation of light at the nanometer scale level and adds another
tool. The ability to work with light and
metamaterials is continuing to evolve and reminds me of the swift advance in
silica and is as important.
Step by step we are on the road
to packing everything inside a crystal manufactured to do it all. Remember the
gem in Star Wars? It is well on the way.
It also continues to tell us that
capturing an alien artifact is at best a hint to technological development
although reverse engineering the UFO is easy in itself with the difficulty in
the details which we are now sorting out.
Do you realize that a gem able to
project a holograph no longer looks too impossible?
'Nanoantennas' show promise in optical innovations
December 22, 2011
The image in the upper left shows a schematic for an array of gold
"plasmonic nanoantennas" able to precisely manipulate light in new
ways, a technology that could make possible a range of optical innovations
such as more powerful microscopes, telecommunications and computers. At
upper right is a scanning electron microscope image of the structures. The
figure below shows the experimentally measured refraction angle versus
incidence angle for light, demonstrating how the nanoantennas alter the
refraction. (Purdue
University Birck
Nanotechnology Center
WEST LAFAYETTE, Ind. – Researchers have shown how arrays of tiny
"plasmonic nanoantennas" are able to precisely manipulate light in
new ways that could make possible a range of optical innovations such as more
powerful microscopes, telecommunications and computers.
The researchers at Purdue
University
"By abruptly changing the phase we can dramatically modify how
light propagates, and that opens up the possibility of many potential
applications," said Vladimir Shalaev, scientific director of
nanophotonics at Purdue's Birck Nanotechnology Center and a distinguished professor of
electrical and computer engineering.
Findings are described in a paper to be published online Thursday (Dec.
22) in the journal Science.
The new work at Purdue extends findings by researchers led by Federico
Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes
Senior Research Fellow in Electrical Engineering at the Harvard School of
Engineering and Applied Sciences. In that work, described in an October Science paper,
Harvard researchers modified Snell's law, a long-held formula used to describe
how light reflects and refracts, or bends, while passing from one material into
another.
"What they pointed out was revolutionary," Shalaev said.
Until now, Snell's law has implied that when light passes from one
material to another there are no abrupt phase changes along the interface
between the materials. Harvard researchers, however, conducted experiments
showing that the phase of light and the propagation direction can be changed
dramatically by using new types of structures called metamaterials, which in
this case were based on an array of antennas.
The Purdue researchers took the work a step further, creating arrays of
nanoantennas and changing the phase and propagation direction of light over a
broad range of near-infrared light. The paper was written by doctoral students
Xingjie Ni and Naresh K. Emani, principal research scientist Alexander V.
Kildishev, assistant professor Alexandra Boltasseva, and Shalaev.
The wavelength size manipulated by the antennas in the Purdue experiment
ranges from 1 to 1.9 microns.
"The near infrared, specifically a wavelength of 1.5 microns, is
essential for telecommunications," Shalaev said. "Information is
transmitted across optical fibers using this wavelength, which makes this
innovation potentially practical for advances in telecommunications."
The Harvard researchers predicted how to modify Snell's law and
demonstrated the principle at one wavelength.
"We have extended the Harvard team's applications to the near
infrared, which is important, and we also showed that it's not a single
frequency effect, it's a very broadband effect," Shalaev said.
"Having a broadband effect potentially offers a range of technological
applications."
The innovation could bring technologies for steering and shaping
laser beams for military and communications applications, nanocircuits for
computers that use light to process information, and new types of powerful
lenses for microscopes.
Critical to the advance is the ability to alter light so that it
exhibits "anomalous" behavior: notably, it bends in ways not possible
using conventional materials by radically altering its refraction, a process
that occurs as electromagnetic waves, including light, bend when passing from
one material into another.
Scientists measure this bending of radiation by its "index of
refraction." Refraction causes the bent-stick-in-water effect, which
occurs when a stick placed in a glass of water appears bent when viewed from
the outside. Each material has its own refraction index, which describes how
much light will bend in that particular material. All natural materials, such
as glass, air and water, have positive refractive indices.
However, the nanoantenna arrays can cause light to bend in a wide
range of angles including negative angles of refraction.
"Importantly, such dramatic deviation from the conventional
Snell's law governing reflection and refraction occurs when light passes
through structures that are actually much thinner than the width of the light's
wavelengths, which is not possible using natural materials," Shalaev said.
"Also, not only the bending effect, refraction, but also the reflection of
light can be dramatically modified by the antenna arrays on the interface, as
the experiments showed."
The nanoantennas are V-shaped structures made of gold and formed on top
of a silicon layer. They are an example of metamaterials, which typically
include so-called plasmonic structures that conduct clouds of electrons called
plasmons. The antennas themselves have a width of 40 nanometers, or billionths
of a meter, and researchers have demonstrated they are able to transmit light
through an ultrathin "plasmonic nanoantenna layer" about 50 times
smaller than the wavelength of light it is transmitting.
"This ultrathin layer of plasmonic nanoantennas makes the phase of
light change strongly and abruptly, causing light to change its propagation
direction, as required by the momentum conservation for light passing through
the interface between materials," Shalaev said.
The work has been funded by the U.S.
Writer: Emil Venere, 765-494-4709, venere@purdue.edu
Source: Vladimir Shalaev, 765-494-9855, shalaev@ecn.purdue.edu
Note to Journalists: A copy of the research paper is available by
contacting the Science Press Package team at 202-326-6440, scipak@aaas.org
ABSTRACT
Broadband Light Bending with
Plasmonic Nanoantennas
Xingjie Ni, Naresh K. Emani,
Alexander V. Kildishev, Alexandra Boltasseva, and Vladimir M. Shalaev*†
School of Electrical and Computer
Engineering and Birck Nanotechnology Center ,
Purdue University
The precise manipulation of a
propagating wave using phase control is a fundamental building block of optical
systems. The wave front of a light beam propagating across an interface can be
modified arbitrarily by introducing abrupt phase changes. We experimentally
demonstrate unparalleled wave-front control in a broadband, optical wavelength
range from 1.0 �m to 1.9 �m. This is accomplished by using
an extremely thin plasmonic layer (~λ/50) consisting of an optical nanoantenna
array that provides subwavelength phase manipulation on light propagating
across the interface. Anomalous light-bending phenomena, including negative
angles of refraction and reflection, are observed in the operational wavelength
range.
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