An electrical engineer at the University of Texas
at Austin has made a laser light blink while passing
through a miniaturized silicon chip, a major step
toward developing commercially viable optical interconnects
for high performance computers and other devices.
Researchers for decades have sought to harness light
as a messenger on silicon chips because light can
move thousands of times faster through solid materials
than electrons and can carry more information at
once, while requiring less energy.
Ray Chen, a professor of electrical engineering,
and graduate students Wei Jiang, YongQiang Jiang
and Lanlan Gu created a chip made of silicon “photonic
crystals” whose complex internal structure slowed
light traveling through the chip. The laser light
slowed down enough that a small electric current
could alter, or modulate, the pattern of light transmission.
“We were able to get our new silicon modulator to
control the transmission of laser light, while using
10 times less power than normally needed for silicon
modulators,” said Chen, who holds the Temple Foundation
Endowed Faculty Fellowship No. 4.
He will give an invited talk about the latest update
on the miniaturized device on Jan. 25, at the Optoelectronics
2006 Symposia of the SPIE Photonics West Conference
in San Jose, Calif.
For light to encode meaningful information, its
intensity or other characteristics need to be modulated,
just as air that passes through a person's vocal
cords is modulated to produce speech sounds by actions
that include moving the lips and tongue. Because
Chen was able to modify light using electric current,
which itself is modifiable, he expects to be able
to modulate the light to blink on and off at different
rates, or to change in intensity.
Once such silicon modulators are combined with lasers
on a silicon platform, these optical chips could
become a mainstay of consumer electronic devices,
telecommunication systems, biosensors and other devices.
In computers, the light-modulating chips would primarily
serve to send information between a computer's microprocessors
and its memory, a process called interconnection.
“In a Pentium 4, over 50 percent of the computer's
power is consumed by interconnection,” Chen said.
Other advantages of optical chips based on silicon
photonic crystals would include their reduced risk
of overheating due to lower power needs, the ability
to fabricate optical chips primarily with traditional
mass-production practices in a silicon foundry and
the expected smaller size of optical modulators and
other optical silicon elements of the future.
Chen initially published findings on the silicon
modulator in the Nov. 28, 2005, issue of the journal
Applied Physics Letters. That article described how
less than 3 milliwatts of power was needed for light
modulation. The length of the special silicon chip
the light needed to travel before being modifiable
was 80 micrometers (.08 millimeters). That is about
10 times shorter than the best conventional silicon
optical modulators. Smaller components help drive
manufacturing costs down,and also transmit signals
The shortened length was possible because Chen's
laboratory designed the silicon photonic crystals
that are the key component of the modulator to have
large regions of regularly spaced, nanosize holes
that light would have to traverse. Navigating the
Swiss cheese-like regions of the crystals, called
line defects, slowed the light's passage considerably.
Since the November publication, Chen's laboratory
has continued evaluating the specialized silicon
chips and learning how to change the blinking rate
of laser light traversing their silicon modulator.
This research is supported by the U.S. Air Force
Office of Scientific Research. Jiang is now a research
scientist at Omega Optics Inc. in Austin, Texas.
For photos of Dr. Chen, go to: www.engr.utexas.edu/news/action_shots/pages/chen.cfm .
About UT's College of Engineering:
The University of Texas College of Engineering is ranked 11th among almost
200 engineering colleges nationwide, according to U.S. News and World Report.
With the nation's third highest percentage of faculty elected members of the
National Academy of Engineering, the College's 6,500 students gain exposure
to the nation's finest engineering practitioners.
Appropriately, the College's logo, an embellished checkmark used by the first
UT engineering dean to denote high quality student work, is the nation's oldest
quality symbol. The College maintains a web site at http://www.engr.utexas.edu