Super Fast Optical Communications Link Sets Crucial Power Efficiency Record
There is a little known but absolutely crucial component for the largest supercomputers and datacenters: Vertical-Cavity Surface-Emitting Lasers, or short VCSEL (pronounced VykSEL). These microscopic small semiconductor lasers, comparable to LEDs, are at the core of the fastest fiber-optical cables that exist and that are necessary to connect the numerous components in a large server farm, and are also key components of many other high-tech applications like laser pico-projectors, touch screens, medical devices and 3D printers.
There is no end to the gradual acceleration of computer speeds, resulting in the exploding exponential curve that we have come to know and expect. But high-speed data transmission on the principle of fiber-optics was not accelerating as fast as the raw computing power of ever smaller chips during the past years. This is changing now as the VCSEL technology that enables several times faster data-rates is maturing. VCSELs are made with the same methods and material, silicon, as microprocessors and thus become ever smaller and more efficient, just like the chips. These VCSELs and the corresponding photodetectors can be further enhanced by nanotechnological tools and materials to further increase their sensitivity and specification, and at the same time shrink them to the size of atoms.
The rapid improvements in semiconductor laser technology are also expected to drive a surge in laser pico-projectors over the coming years. In addition, many other applications such as laser printers, industrial cutting, cosmetics and medical applications will drive rapid deployment of miniature semiconductor lasers.
Leading companies in this field are currently massproducing VCSEL chips with cutting-edge data rates of 14 Gbit/s, for example Finisar or U-L-M Photonics, based in Germany. The fastest supercomputers and datacenters, requiring high data transfer capacities over longer distances (up to 300 meter), can now use InfiniBand cables powered by VCSEL arrays of 12 with a maximum of 168 Gbit/s which don't increase overall heat or even melt thanks to much lower power requirements than thicker and shorter distance copper cables.
While this enables the present construction of efficient petaflop supercomputers, even higher data rates are needed to construct the internal networks required by a future generation of supercomputers with over one exaflop of computing power.
According to the relevant InfiniBand industry association, market available "bandwidths [should be] reaching 300Gb/s data rate EDR by 2013. The newly defined link speeds are designed to keep the rate of performance increase in line with systems-level performance increases."
This means that the next generation of fiber-optics needs VCESLs with a speed of 25 Gbit/s per link (a single fiber). Accelerating VCSEL faces the same challenge as microprocessors: Higher frequencies means more heat, which can fry the fragile components. A team of IBM researchers working on a U.S. Defense Advanced Research Projects Agency (DARPA)-funded program claim that they have now found a way to achieve the 25 Gbit/s with the lowest power consumption, and thus heat, to date. They cut the power in half, compared to the previous power efficiency record, using 24 milliwatts of total power, or 1 pJ/bit (one picoJoule per bit). A Joule is measure of the amount of energy required to produce one watt of power for one second. A picoJoule is 10-12 Joule.
The researchers combined innovative circuits in IBM's 32-nanometer silicon-on-insulator complementary metal-oxide-semiconductor (SOI CMOS) technology with VCSELs fabricated by Sumitomo Electric Device Innovations USA (formerly Emcore).
Scientists predict that the exascale supercomputers of the future will enable them to model the global climate, run molecular-level simulations of entire cells, design nanostructures, and more. Exascale refers to speeds in the range of 1018 computations per second (more precisely, 1018 floating point operations per second).
"We envision machines reaching the exascale mark around 2020, but a great deal of research must be done to make this possible," says Jonathan E. Proesel, a research staff member at the IBM T. J. Watson Research Center in Yorktown Heights, N.Y.
To reach that mark, researchers must develop a way to quickly move massive amounts of data within the supercomputer while keeping power consumption in check.
"We're continuing the push for lower power and higher speed in optical communications. There will always be demand to move more data with less energy, and that's what we're working toward," Proesel says.
The development will be presented at the Optical Fiber Communication Conference and Exposition/National Fiber Optic Engineers Conference (OFC/NFOEC) in Anaheim, Calif. March 17-21, where most of the global companies of the sector will exhibit, including the mentioned Finisar and U-L-M Photonics.
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