Researchers at UCLA Engineering
Announce Breakthrough in Silicon Photonics Devices
Turning the tables
on chip power consumption: new silicon optical amplifiers generate
electrical power by harvesting energy
Building on a series of recent
breakthroughs in silicon photonics, researchers at the UCLA
Henry Samueli School of Engineering and Applied Science have
developed a novel approach to silicon devices that combines
light amplification with a photovoltaic — or solar panel
— effect.
In a study to be presented today
at the 2006 International Optical Amplifiers and Applications
Conference in Vancouver, Canada, UCLA Engineering researchers
report that not only can optical amplification in silicon be
achieved with zero power consumption, but power can now be generated
in the process.
The team’s research shows
that silicon Raman amplifiers possess nonlinear photovoltaic
properties, a phenomenon related to power generation in solar
cells. In 2004, the same group at UCLA Engineering demonstrated
the first silicon laser, a device that took advantage of Raman
amplification.
“After dominating the electronics
industry for decades, silicon is now on the verge of becoming
the material of choice for the photonics industry, the traditional
stronghold of today’s semiconductors,” said Bahram
Jalali, the UCLA Engineering professor who led researcher Sasan
Fathpour and graduate student Kevin Tsia in making the recent
discovery.
The amount of information that
can be sent through an optical wire is related directly to the
intensity of the light. In order to perform some of the key
functions in optical networking — such as amplification,
wavelength conversion and optical switching — silicon
must be illuminated with high-intensity light to take advantage
of its nonlinear properties. One example is the Raman effect,
a phenomenon that occurs at high optical intensities and is
behind many recent breakthroughs in silicon photonics, including
the first optical amplifiers and lasers made in silicon.
The fundamental challenge in silicon
photonics is the material stops being transparent at high optical
intensities, making light unable to pass through.
“As light intensifies in
silicon, it generates electrons through a process called ‘two
photon absorption.’ Excess electrons absorb the light
and turn it into heat. Not only is the light and the data-carrying
capacity lost, the phenomenon exacerbates one of the main obstacles
in the semiconductor industry, which is excessive heating of
chips. The optical loss also makes it all but impossible to
create optical amplifiers and lasers that operate continuously,”
Jalali said.
In previous attempts to deal with
this challenge, a diode attached to the chip has been used to
“vacuum” out the electrons that block light. This
approach presents further problems, however, because the vacuum
adds an additional watt of heat onto the chip — nearly
a million times the power that a single transistor consumes
in a digital circuit.
“In the past, two-photon
absorption in silicon has resulted in significant loss for high
power Raman amplifiers and lasers, reducing efficiency and necessitating
complex mitigation schemes. UCLA Engineering’s new development
will enable recycling power that would otherwise be lost. In
space and military laser systems, the impact of device efficiency
on electrical power and thermal management is a prime consideration,”
said Dr. Robert R. Rice, senior scientist at Northrop Grumman
Space Technology’s Laser and Sensor Product Center.
The challenge of power dissipation
in traditional silicon semiconductors already is so severe that
it threatens to halt the continued advance of the technology
described by Moore’s law.
(Gordon Moore, one of Intel’s
founders, predicted in 1965 that innovative research would allow
for a doubling of the number of transistors in a given space
every year. In 1975, he adjusted this prediction to a doubling
every two years.)
Because the UCLA Engineering team’s
discovery creates an advantage in heat dissipation, it represents
a new perspective.
“The progress in silicon
Raman lasers at UCLA Engineering by professor Bahram Jalali
and his group has been very impressive, not only offering obvious
benefits in photonic systems, but also opening up an entirely
new approach,” Rice added.
“This discovery is a step
forward and makes it much more likely that the photonics and
electronics will converge. If they do, many applications that
silicon photonics has promised will come to fruition,”
Jalali said.
Silicon photonics technology has
the potential to use the power of optical networking inside
computers and to create new generation of miniaturized and low-cost
photonic components, among other applications.
Jalali’s research at UCLA
Engineering has been funded by the U.S. Department of Defense
through the Defense Advanced Research Project Agency. The research
also was co sponsored by the Northrop Grumman Corp.
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