An example of a metamaterial. |
Electrical
engineers at Duke University have developed a material that allows them
to manipulate light in much the same way that electronics manipulate
flowing electrons.
The
researchers say the results of their latest proof-of-concept
experiments could lead to the replacement of electrical components with
those based on optical technologies. Light-based devices would enable
faster and more efficient transmission of information, much in the same
way that replacing wires with optical fibers revolutionized the
telecommunications industry.
The
breakthrough revolves around a novel man-made structure known as a
metamaterial. These exotic composite materials are not so much a single
substance, but an entire structure that can be engineered to exhibit
properties not readily found in nature. The structure used in these
experiments resembles a miniature set of tan Venetian blinds.
When
light passes through a material, even though it may be reflected,
refracted or weakened along the way, it is still the same light coming
out. This is known as linearity.
“For
highly intense light, however, certain ‘nonlinear’ materials violate
this rule of thumb, converting the incoming energy into a brand new beam
of light at twice the original frequency, called the second-harmonic,”
said Alec Rose, graduate student in the laboratory of David R. Smith,
William Bevan Professor of electrical and computer engineering at Duke’s
Pratt School of Engineering.
As
an example, he cited the crystal in some laser pointers, which
transforms the normal laser light into another beam of a different
color, which would be the second-harmonic. Though they contain nonlinear
properties, designing such devices requires a great deal of time and
effort to be able to control the direction of the second harmonic, and
natural nonlinear materials are quite weak, Rose said.
“Normally,
this frequency-doubling process occurs over a distance of many
wavelengths, and the direction in which the second-harmonic travels is
strictly determined by whatever nonlinear material is used,” Rose said.
“Using the novel metamaterials at microwave frequencies, we were able to
fabricate a nonlinear device capable of ‘steering’ this
second-harmonic. The device simultaneously doubled and reflected
incoming waves in the direction we wanted.”
The
research results were published online in the journal Physical Review
Letters. It was supported by the Air Force Office of Scientific
Research. Smith’s team was the first to demonstrate that similar
metamaterials could act as a cloaking device in 2006 and a next
generation lens in 2009.
“This
magnitude of control over light is unique to nonlinear metamaterials,
and can have important consequences in all-optical communications, where
the ability to manipulate light is crucial,” Rose said.
The
device, which measures six inches by eight inches and about an inch
high, is made of individual pieces of the same fiberglass material used
in circuit boards arranged in parallel rows. Each piece is etched with
copper circles. Each copper circle has a tiny gap that is spanned by a
diode, which when excited by light passing through it, breaks its
natural symmetry, creating non-linearity.
“The
trend in telecommunications is definitely optical,” Rose said. “To be
able to control light in the same manner that electronics control
currents will be an important step in transforming telecommunications
technologies.”
Duke graduate student Da Huang was also a member of the team.
