Home' Technology Review : November December 2007 Contents From the Labs
TECHNOLOGY REVIEW /
FROM THE LABS 91
form for testing heart dr ugs. (The
devices provide an easy way to moni-
tor the e ect of dr ugs on heart tissue.)
Eventually, they could be used in new
types of robots that can change shape,
grip objects, and propel themselves.
METHODS: The researchers used a
fabrication method called spin coating
to make ultrathin elastic lms; then
they applied patterns of proteins to the
lms. Finally, they added heart-muscle
cells; guided by the protein patterns, the
cells organized themselves into work-
ing muscle tissue. To make the various
devices, the researchers cut the muscu-
lar thin lms into speci c shapes (such
as a triangle that resembled a sh s tail)
and changed the alignment of the cells.
The devices, which must remain in a
solution that keeps the muscles alive,
can be controlled by electronic signals
sent through the solution.
NEXT STEPS: The researchers are
working to create devices that use
human muscle tissue, perhaps grown
from stem cells; such devices could be
used in drug testing or to patch dam-
aged heart muscle. So far, the muscle
tissue sur vives for only a few weeks.
For robotics applications, the scientists
may combine heart muscle with other
types of cells to increase longevity.
Faster Silicon Laser
A new design could yield a more
practical light source for
S OU RCE: "Mode-Locked Silicon
Brian R. Koch et al.
Optics Express 15: 11225--11233
RESULTS: Researchers have designed
a stable, electrically pumped silicon-
based laser that emits ultrashort pulses
of light at a frequency of 40 gigahertz.
WHY IT MATTERS: In modern tele-
communications networks, bits of
information are carried by laser light.
Currently, the lasers that generate the
light are made in dedicated indium
phosphorous clean rooms. Silicon-
based lasers that could be made on
existing high-volume semiconductor
manufacturing lines would be much
cheaper. Until now, silicon lasers have
been incapable of emitting pulses of
light that are short enough and have
high enough frequencies for use in
telecommunications networks. The
researchers hope that the new silicon-
based device could replace the costlier
lasers now used in optical networks.
METHODS: The construction of the
device begins with a wafer in which a
layer of silicon dioxide is sandwiched
between two layers of silicon. In the
top layer of silicon, the researchers
etch a channel called a waveguide. To
the top of the wafer they bond strips
of indium phosphide; when current
is applied to electrical contacts, the
strips emit light that bounces back
and forth inside the waveguide. A
small amount of the light sneaks back
into the indium phosphide, where it is
ampli ed and emerges as laser light.
In order to control the pulses of light
emitted by the laser, the researchers
had to make sure that the waveguides
were of a precise length, and that
light-amplifying and light-absorbing
regions of the device were electrically
isolated from each other.
NEXT STEPS: Currently, the laser s
perfor mance drops at the high tem-
peratures that can be characteristic of
network hardware. The researchers
need to modify the device so it can
withstand these temperatures, and it
will have to pass other tests of robust-
ness. In addition, the researchers are
exploring the best way to combine the
laser with other components, such as
modulators, to make silicon-based
Why Wi-Fi Fails
A diagnostic system determines
where and why buildingwide
SO U RCE: "Automating Cross-Layer
Diagnosis of Enterprise Wireless
Yu-Chung Cheng et al.
Proceedings of the ACM Sigcomm Conference,
Kyoto, Japan, August 2007
RESULTS: Researchers at the Univer-
sity of Califor nia, San Diego, have
developed a system that tracks wire-
less tra c in a building and deter-
mines precisely what causes signals to
dip, tra c to slow, and laptops to get
kicked o the network.
PETER ALLEN, UNIVERSITY OF CALIFORNIA, SANTA BARBARA
This image depicts a new design for hybrid
silicon lasers. Prototypes of the lasers are
fast enough for use in telecom networks.
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