[ExI] Repulsive' Side To Light Force Could Control Nanodevices

Emlyn emlynoregan at gmail.com
Wed Jul 15 05:51:30 UTC 2009

My physics knowledge gets me to "step in hole, fall down" level, so I
can't evaluate this. It looks exciting to this caveman.


'Repulsive' Side To Light Force Could Control Nanodevices

ScienceDaily (July 13, 2009) — A team of Yale University researchers
has discovered a "repulsive" light force that can be used to control
components on silicon microchips, meaning future nanodevices could be
controlled by light rather than electricity.

The team previously discovered an "attractive" force of light and
showed how it could be manipulated to move components in
semiconducting micro- and nano-electrical systems—tiny mechanical
switches on a chip. The scientists have now uncovered a complementary
repulsive force. Researchers had theorized the existence of both the
attractive and repulsive forces since 2005, but the latter had
remained unproven until now. The team, led by Hong Tang, assistant
professor at Yale's School of Engineering & Applied Science, reports
its findings in the July 13 edition of Nature Photonics's advanced
online publication.

"This completes the picture," Tang said. "We've shown that this is
indeed a bipolar light force with both an attractive and repulsive

The attractive and repulsive light forces Tang's team discovered are
separate from the force created by light's radiation pressure, which
pushes against an object as light shines on it. Instead, they push out
or pull in sideways from the direction the light travels.

Previously, the engineers used the attractive force they discovered to
move components on the silicon chip in one direction, such as pulling
on a nanoscale switch to open it, but were unable to push it in the
opposite direction.

Using both forces means they can now have complete control and can
manipulate components in both directions. "We've demonstrated that
these are tunable forces we can engineer," Tang said.

In order to create the repulsive force, or the "push," on a silicon
chip, the team split a beam of infrared light into two separate beams
and forced each one to travel a different length of silicon nanowire,
called a waveguide. As a result, the two light beams became out of
phase with one another, creating a repulsive force with an intensity
that can be controlled—the more out of phase the two light beams, the
stronger the force.

"We can control how the light beams interact," said Mo Li, a
postdoctoral associate in electrical engineering at Yale and lead
author of the paper. "This is not possible in free space—it is only
possible when light is confined in the nanoscale waveguides that are
placed so close to each other on the chip."

"The light force is intriguing because it works in the opposite way as
charged objects," said Wolfram Pernice, another postdoctoral fellow in
Tang's group. "Opposite charges attract each other, whereas
out-of-phase light beams repel each other in this case."

These light forces may one day control telecommunications devices that
would require far less power but would be much faster than today's
conventional counterparts, Tang said. An added benefit of using light
rather than electricity is that it can be routed through a circuit
with almost no interference in signal, and it eliminates the need to
lay down large numbers of electrical wires.

Funding for the project includes a seed grant from the U.S. Defense
Advanced Research Projects Agency and a Young Faculty Award from the
National Science Foundation.


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