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This illustration shows a new "all-silicon passive optical diode," a device small enough to fit millions on a computer chip that could lead to faster, more powerful information processing and supercomputers. The device has been developed by Purdue University researchers. Image: Birck Nanotechnology Center, Purdue University
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Researchers have created a new type of optical device
small enough to fit millions on a computer chip that could lead to faster, more
powerful information processing and supercomputers.
The "passive optical diode" is made from two
tiny silicon rings measuring 10 um in diameter. Unlike other optical diodes, it
does not require external assistance to transmit signals and can be readily
integrated into computer chips.
The diode is capable of "nonreciprocal transmission,"
meaning it transmits signals in only one direction, making it capable of
information processing, says Minghao Qi, an associate professor of electrical
and computer engineering at Purdue University.
"This one-way transmission is the most fundamental
part of a logic circuit, so our diodes open the door to optical information
processing," says Qi, working with a team also led by Andrew Weiner,
Purdue's Scifres Family Distinguished Professor of Electrical and Computer
Engineering.
The diodes are described in a paper in Science. The paper was written by
graduate students Li Fan, Jian Wang, Leo Varghese, Hao Shen, and Ben Niu;
research associate Yi Xuan; and Weiner and Qi.
Although fiber optic cables are instrumental in
transmitting large quantities of data across oceans and continents, information
processing is slowed and the data are susceptible to cyber attack when optical
signals must be translated into electronic signals for use in computers, and
vice versa.
"This translation requires expensive equipment,"
Wang says. "What you'd rather be able to do is plug the fiber directly
into computers with no translation needed, and then you get a lot of bandwidth
and security."
Electronic diodes constitute critical junctions in
transistors and help enable integrated circuits to switch on and off and to
process information. The new optical diodes are compatible with industry
manufacturing processes for complementary metal-oxide-semiconductors, or CMOS,
used to produce computer chips, Fan says.
"These diodes are very compact, and they have other
attributes that make them attractive as a potential component for future
photonic information processing chips," she says.
The new optical diodes could make for faster and more
secure information processing by eliminating the need for this translation. The
devices, which are nearly ready for commercialization, also could lead to
faster, more powerful supercomputers by using them to connect numerous
processors together.
"The major factor limiting supercomputers today is
the speed and bandwidth of communication between the individual superchips in
the system," Varghese says. "Our optical diode may be a component in
optical interconnect systems that could eliminate such a bottleneck."
Infrared light from a laser at telecommunication wavelength
goes through an optical fiber and is guided by a microstructure called a
waveguide. It then passes sequentially through two silicon rings and undergoes
"nonlinear interaction" while inside the tiny rings. Depending on
which ring the light enters first, it will either pass in the forward direction
or be dissipated in the backward direction, making for one-way transmission.
The rings can be tuned by heating them using a "microheater," which
changes the wavelengths at which they transmit, making it possible to handle a
broad frequency range.
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