technology VCSELs Abolishing copper interconnects
Rocketing demands for data transfer are signaling a switch from copper interconnects to those based on optical fiber. But these new links will only receive widespread adoption when they are paired with ultra-high-speed sources, such as our VCSELs that combine record-breaking modulation speeds with high temperature operation, say Werner Hofmann and Dieter Bimberg from TU-Berlin.
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oday’s interconnects, like those of yesteryear, are predominantly made from copper. This material is readily available and easy to process, but it is far from ideal for making data transmission links. Speeds are limited due to high levels of damping that suppress signal-to-noise ratios, and crosstalk plagues interconnects at higher frequencies.
One can get around these weaknesses by moving to higher signal levels and multiple parallel links. This has happened with CPUs, which incorporate more and more pins and use bigger and bigger heat-sinks for cooling. But this approach has its limits, and the days of copper- based technology are vanishing fast for the supercomputer.
In this arena, every new generation of machine must deliver a tremendous hike in computational speed, while costing little more than its predecessor and consuming hardly any more energy. To meet these requirements, the PetaFlop Supercomputer that IBM unveiled in 2008 incorporated 48,000 optical links. And according to this industry’s roadmap, the ExaFlop mainframes of the next
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www.compoundsemiconductor.net June 2012
decade will feature a staggering 320 million optical interconnects, each performing at far greater levels than those in the 2008 machine: Data transmission through each link will have to be five times higher, energy consumption 50 times less, and the price lower by a factor of 400. Improvements in energy consumption must be this great, because the vast majority of energy consumed by these computers takes place in interconnects.
The delay in the uptake optical interconnects is partly due to strong competition from copper links, which are cheap to produce. Cash has been tight in the optical interconnect industry, hampering investment in new technologies, and big players in the optics industry have focused on markets offering a better short-term return on investment. But that tide is now turning. There is growing realization that optical interconnect technologies are needed, and companies are injecting large sums of cash into their R&D departments to make this happen.
Although funding is flowing, success is never instantaneous. This explains the dilemma that is
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