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Si Nanophotonics Advanced

Photonics.com
Dec 2007
YORKTOWN HEIGHTS, N.Y., Dec. 6, 2007 -- Silicon research announced today uses light instead of copper wires to transmit information through the "brains" on a chip. The development could potentially lead to supercomputers -- which today are power-hungry, huge, and run hot -- that fit into a laptop PC and operate faster, cooler, and more energy efficient.

In a paper published in the journal Optics Express, IBM researchers detailed what they said is a significant milestone in the quest to send information between multiple cores -- or "brains" -- on a chip using pulses of light through silicon, instead of electrical signals on wires, and ultimately build supercomputers-on-a-chip.
OpticalModulator1.jpg
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 (red) 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, in 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 (1s and 0s) from electrical input pulses into pulses of light. (Images courtesy IBM)
The researchers used a silicon Mach-Zehnder electro-optic modulator to convert electrical signals into pulses of light. The IBM modulator is 100 to 1000 times smaller in size compared to previously demonstrated modulators of its kind, paving the way for many such devices and eventually complete optical routing networks to be integrated onto a single chip, the researchers said. This could significantly reduce cost, energy and heat while increasing communications bandwidth between the cores more than a hundred times over wired chips.
OpticalModulator2.jpg
IBM’s optical modulator uses silicon nanophotonic waveguides to control the flow of light on a silicon chip. Digital electrical signals are applied to the p+-i-n+ doped silicon nanophotonic waveguide through the electrodes (gold). Electrical charges (holes – green particles; electrons – red particles) are injected into the waveguide and change the optical properties of silicon, which is used to perform the modulation function.
"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," said T.C. Chen, PhD, vice president, Science and Technology, IBM Research. "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."

One of today's most advanced chips, IBM's Cell processor which powers the Sony Playstation 3, contains nine cores on a single chip. The new technology aims to enable a power-efficient method to connect hundreds or thousands of cores together on a tiny chip by eliminating the wires required to connect them. Using light instead of wires to send information between the cores can be 100 times faster and use 10 times less power than wires.

"We believe this is a major advancement in the field of on-chip silicon nanophotonics," said Will Green, PhD, the lead IBM scientist on the project. "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."
OpticalModulator3.jpg
The waveguides are made of tiny silicon strips (purple) with dimensions 200 times smaller than the diameter of a human hair, in a silicon-on-insulator (SOI) wafer. Light is strongly confined within the silicon nanophotonic waveguide as shown by the colored concentric ellipses overlaid with the waveguide image. The strong confinement of light allows the modulator to be dramatically scaled down in size.
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 is delivered to the optical modulator, which acts as a very fast "shutter" which controls whether the input laser is blocked or transmitted to the output waveguide. 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. In this way, the device "modulates" the intensity of the input laser beam, and the modulator converts a stream of digital bits (1s and 0s) from electrical signals into light pulses.

This work was partially supported by DARPA through the Defense Sciences Office program Slowing, Storing and Processing Light.

For more information, visit: www.research.ibm.com/photonics


GLOSSARY
beam
1. A bundle of light rays that may be parallel, converging or diverging. 2. A concentrated, unidirectional stream of particles. 3. A concentrated, unidirectional flow of electromagnetic waves.
chip
1. A localized fracture at the end of a cleaved optical fiber or on a glass surface. 2. An integrated circuit.
light
Electromagnetic radiation detectable by the eye, ranging in wavelength from about 400 to 750 nm. In photonic applications light can be considered to cover the nonvisible portion of the spectrum which includes the ultraviolet and the infrared.
modulator
See acousto-optic modulator; electro-optic modulator.
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
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