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IBM uses light to build supercomputers-on-a-chip
By Ann Steffora Mutschler, Senior Editor -- Electronic News, 12/6/2007
Thanks in part to a breakthrough by IBM scientists, supercomputers that consist of thousands of individual processor “brains” connected by miles of copper wires could one day fit into a laptop PC; and while today’s supercomputers can use the equivalent energy required to power hundreds of homes, these future tiny supercomputers-on-a-chip would expend the energy of a light bulb.
In a paper published in the journal Optics Express, IBM researchers have detailed what they believe is a significant milestone in the quest to send information between multiple cores on a chip using pulses of light through silicon, instead of electrical signals on wires.
The breakthrough is known as a silicon Mach-Zehnder electro-optic modulator and converts electrical signals into pulses of light.
IBM said its modulator is 100 to 1,000 times smaller than previously-demonstrated modulators of its kind, and is expected to eventually allow for complete optical routing networks to be integrated onto a single chip, which could significantly reduce cost, energy and heat while increasing communications bandwidth between the cores more than a hundred times over wired chips.
Dr. T.C. Chen, VP of science and technology at IBM Research said in a statement, “Work is underway within IBM and in the industry to pack many more computing cores on a single chip, but today’s on-chip communications technology would overheat and be far too slow to handle that increase in workload. What we have done is a significant step toward building a vastly smaller and more power-efficient way to connect those cores, in a way that nobody has done before.”
For example, one of the most advanced chips in the world – IBM’s Cell processor which powers the Sony Playstation 3 -- contains nine cores on a single chip. IBM pointed out that its new technology aims to allow a power-efficient method to connect hundreds or thousands of cores together on a tiny chip by eliminating the wires required to connect them, since using light instead of wires to send information between the cores can be 100 times faster and use 10 times less power than wires.
The lead IBM scientist on the project, Dr. Will Green said “We believe this is a major advancement in the field of on-chip silicon nanophotonics. Just like fiber optic networks have enabled the rapid expansion of the Internet by enabling users to exchange huge amounts of data from anywhere in the world, IBM’s technology is bringing similar capabilities to the computer chip.”
IBM explained that its optical modulator (see photo below) performs the function of converting a digital electrical signal carried on a wire, into a series of light pulses, carried on a silicon nanophotonic waveguide.
First, an input laser beam is delivered to the optical modulator, which acts as a very fast "shutter" and controls whether the input laser is blocked or transmitted to the output waveguide. Then, when a digital electrical pulse arrives from a computer core to the modulator, a short pulse of light is allowed to pass through at the optical output and in this way, the device "modulates" the intensity of the input laser beam, and the modulator converts a stream of digital bits ("1"s and "0"s) from electrical signals into light pulses.
The report on this work is titled “Ultra-compact, low RF power, 10 Gb/s silicon Mach-Zehnder modulator” by William M. J. Green, Michael J. Rooks, Lidija Sekaric, and Yurii A. Vlasov of IBM's T.J.Watson Research Center in Yorktown Heights, N.Y.
The work was partially supported by the Defense Advanced Research Projects Agency (DARPA) through the Defense Sciences Office program, “Slowing, Storing and Processing Light.”
Big Blue reminded that it’s pioneering work to move the industry from aluminum to copper wiring, unveiled in 1997, gave the industry an immediate 35 percent reduction in electron flow resistance and a 15 percent boost in chip performance.
Since then, IBM scientists have continued to drive performance improvements to continue the path of Moore's Law.
Just this year, IBM announced its high-k metal gate technology in January, embedded DRAM technology in February, 3-D chip stacking in April, and “airgap” technology in May.
To watch a video on the optical modulator, click here.
Source: IBM
IBM's optical modulator performs the function of converting a digital electrical signal carried on a wire, into a series of light pulses, carried on a silicon nanophotonic waveguide. First, an input laser beam (marked by red color) is delivered to the optical modulator. The optical modulator (black box with IBM logo) is basically a very fast “shutter” which controls whether the input laser is blocked or transmitted to the output waveguide. When a digital electrical pulse (a “1” bit marked by yellow) arrives from the left at the modulator, a short pulse of light is allowed to pass through at the optical output on the right. When there is no electrical pulse at the modulator (a “0” bit), the modulator blocks light from passing through at the optical output. In this way, the device “modulates” the intensity of the input laser beam, and the modulator converts a stream of digital bits (“1”s and “0”s) from electrical input pulses into pulses of light.
