chips linked by light
Technology Research News
One of the challenges of making computer
chips is efficiently ferrying information into and out of them. This is
usually done via metal wires. Researchers from Johns Hopkins University
have worked out a way to speed information to and from chips using light
rather than wire.
The method is a way of using the fiber optics technology that make high-speed
networks fast to bring information directly onto a chip. The ones and
zeros of digital information are transmitted through wires using the absence
or presence of electrical current. The same type of information is transmitted
through fiber optics using the absence or presence of a pulse of light.
Fiber optics is much faster than electronics, because pulses of light
can be sent through fiber much faster than an electrical switch can flip
on and off.
To transmit information to a chip using light, the researchers had to
change the structure of the chip. The new design could speed information
transfer on and off chips by five times.
Computer chips are usually made up of thin slices of the semiconductor
silicon. The researchers added layers of synthetic sapphire, an insulator
that does not conduct electricity, but allows light to pass through.
They used microlasers to beam light perpendicular to the plane of the
wafer, and bonded microdetectors onto the sapphire layer of the chip to
pick up the light transmissions. "The light is transmitted through the
plane of the electronics," said Alyssa Apsel, a graduate student at Johns
Once the signal reaches its destination, it goes through an optical receiver
that transforms the light signal back to an electrical signal that can
be handled by the chip's electrical wiring.
The researchers' prototype is capable of shunting information on and off
the chip at the rate of one gigabit per second, according to Apsel. Four
minutes of full-motion video contain about one gigabit of information.
As the parts of the chip get smaller, chip communications get faster because
information does not have as far to travel. The components of the researchers
prototype are half a micron wide. The next generation of the researchers
chip will have features as small as 0.1 microns, a size equivalent to
today's production electronics, said Apsel. A micron is one thousandth
of a millimeter.
At 0.1 microns, the researchers' design has the potential to run at 5
gigabits per second, said Apsel. Today's production computer chips have
bus speeds that are generally below one gigabit per second. The design
is also fairly power efficient, according to Apsel. The 0.5 micron prototype
uses about 10 microwatts, and the next generation may use less, she said.
The new chip design could be used to improve the internal rates of data
transfer among chips in a computer. It could also be used to improve the
speed of information transfer in future Local Area Networks, said Apsel.
There is also a biological application, she added. "There are uses in
biological sensory systems... which require a higher level of circuit-to-circuit
connectivity than current systems are capable of," she said.
The researchers are working on improving the efficiency of their design,
and producing larger arrays of opto-electronic links. "We would like to
ultimately build very high-performance systems using optical interconnects,"
It will be a few years before the technology can be made practical, Apsel
Apsel's research colleague is Andreas Andreou. They published the research
in the third quarter, 2001 issue of the IEEE Circuits and Systems magazine.
The research was funded by the Army Research Laboratory (ARL) and the
Defense Advanced Research Projects Agency (DARPA).
Timeline: 3-5 years
TRN Categories: Optical Computing, Optoelectronics and Photonics;
Story Type: News
Related Elements: Technical paper, "Silicon on Sapphire
CMOS for Optoelectronic Microsystems," IEEE Circuits and Systems magazine,
third quarter, 2001.
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