Home' Technology Review : May June 2007 Contents From the Labs
102 FROM THE LABS
TECHNOLOGY REVIEW /
particles of di erent materials. The
measurements were made by attaching
particles to the tip of an atomic force
microscope. The interplay of forces
caused the researchers chosen mate-
rials to sort themselves into a work-
NEXT STEPS: To make the bat-
tery more rugged, the researchers
want to replace the liquid electrolyte
used in the prototype with a polymer.
Also, future prototypes could use self-
assembling particles for both elec-
trodes, not just one.
A new type of mirror could make
lasers smaller and more efficient
SOU RCE: "A Surface-Emitting Laser
Incorporating a High-Index-Contrast
Connie J. Chang-Hasnain et al.
Nature Photonics 1, no. 2 (February 2007):
RESULTS: Researchers at the Univer-
sity of California, Berkeley, have over-
hauled one of the main elements of a
laser: the mirror. The new mirror is
thinner than its predecessors and can
be made in fewer steps, simplifying
the laser fabrication process and low-
ering costs. It is also more re ective
than previous mirrors, so it could lead
to more energy-e cient lasers.
WHY IT MATTERS: Many consumer
electronic products use optoelectronic
devices such as lasers that could bene-
t from an e cient, thinner, cheaper
mirror. The mirrors currently used in
many lasers comprise more than 80
layers of alternating thin lms consist-
ing of di erent materials; each layer
adds to the laser s fabrication cost.
The new mirror, by contrast, has only
METHODS: The researchers built
their mirror into a common type of
laser, called a vertical-cavity surface-
emitting laser, that typically consists
of two mirrors sandwiching an "active
region"---the area in which photons are
produced when a current is applied.
Photons within the active region re ect
o the mirrors, and as they bounce
back and forth, their intensity increases.
When it gets high enough, they pass
through the mirrors, producing a beam
of coherent, single-color light.
The new mirror, designed by
Connie Chang-Hasnain, professor
of electrical engineering and com-
puter science at Berkeley, is a grating
composed of thin parallel bars of alu-
minum gallium arsenide, separated
from the rest of the laser by air. The
photons from the active region enter
the aluminum gallium arsenide bars;
then, because of the optical proper-
ties of the junction between the mate-
rial and the air, they take a 90º turn,
re ect o the other bars, come back,
and make another 90º turn into the
active region. There they bounce back
and forth until they are su ciently
ampli ed, pass through the mirrors,
and exit the device.
NEXT STEP: The researchers are
working to integrate the mirror into a
"tunable" laser, which can emit beams
of varying wavelengths of light; such
devices would be useful for telecom-
munications, and for biological and
chemical sensors. In addition, they
are incorporating the mirror into solar
cells, in an e ort to improve e ciency.
Chang-Hasnain is looking for commer-
without a Mouse
Eye-tracking user interface could
provide an alternative
SOU RCE: "EyePoint: Practical Pointing
and Selection Using Gaze and Keyboard"
Manu Kumar et al.
CHI 2007, April 28--May 3, 2007, San Jose, CA
RESULTS: Stanford University PhD
student Manu Kumar has developed
an easy-to-use alternative to the com-
puter mouse: a system that allows a
person to point, click, and perform
everyday mouse actions by looking at
a computer s monitor and tapping a
key on its keyboard.
WHY IT MATTERS: User interfaces
that use eye-tracking technology have
been around for many years and are
sometimes used by disabled people.
But so far, they haven t been easy
enough to use to displace existing
METHODS: The technology uses
standard eye-tracking hardware:
embedded in the bezel of a computer
monitor are infrared light sources and
a camera that captures both the move-
ment of the user s pupil and the re ec-
tion of the infrared light o his or her
cornea. The user looks at, say, a Web
link and then depresses a "hot key" on
the keyboard. The area of the screen
that s being looked at becomes magni-
ed. Then the user narrows his or her
focus within the magni ed region and
releases the hot key, e ectively clicking
through to the link.
NEXT STEP: In studies in which par-
ticipants were asked to type using the
keyboard but move the cursor using the
eye-tracking system, Kumar recorded
an er ror rate close to 20 percent. He
says many errors occur when users
think they are focusing on a target that s
actually in their peripheral vision, and
the eye-tracking technology instead
picks up the area they re really looking
at. Kumar has developed algorithms to
compensate for these errors.
CONNIE J. CHANG-HASNAIN
A new type of mirror (square in center) is
a fraction of the thickness of conventional
mirrors used in semiconductor lasers.
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