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IBM's new optical interconnect may shape the future of supercomputers -- and all the other ones, too

A growing issue involved with the new gamut of multi-core processors, from dual-core to quad-core and beyond, is shuttling data between the cores themselves. Problems arise as the bleeding edge of electrical and thermal physics are pushed by the vanishing space between transistors and now between cores. IBM may have something of a solution for this, they recently announced, in the form of an optical coupler.

Due to the wholly unfair restrictions of physics, there is only so much information that can be sent through copper interconnects. Heat and leakage both contribute to this, as smaller structures are much more prone to self-destruction caused by thermal disintegration and interference from their neighbors in the silicon sea.

Light, it turns out, doesn't have much of an issue with either. IBM thinks it will provide a means to safely connect the growing number of cores being packed onto a single chip.

The optical modulator, known as a Mach-Zehnder elctro-optic modulator, is actually much simpler than it sounds. If you're familiar with Digital Light Processing (DLP) television technology, you already understand the basics. In IBM's modulator, a laser is focused on the device, which is also connected to the copper side of the data bus. Rather than working on a reflection-based technology like DLP, the modulator simply uses the electrical binary to operate a shutter-type mechanism to turn the input laser into pulses. The pulses are then sent along a waveguide to a receiver, and translated back into electrical signal.

The modulator's waveguide structure, as well as the size of the device are both limited by the wavelength of light used. IBM's current generation coupler has a 500nm waveguide, and the device itself is a mere 200 micrometers long, half the wavelength of the laser's light. This makes it easily small enough to fit between current generation multi-core processor cores.

The device is many times more efficient than current bus technology. IBM bills speeds at 100 to 1,000 times faster than electrical, with energy consumption of 50 milliwatts or less. The theoretical speed of the interconnects could virtually eliminate anything similar to an information bottleneck as we know it now. And as any student of science can tell you, less power results in less heat, which means less power wasted as well.

The device, as IBM sees it, will in time allow the power of a supercomputer on a chip that feels at home in a laptop. Reduced heat production and electrical costs will not only benefit laptops and other micro-devices, but businesses with giant servers as well. Less space and less heat equates to less money spent on maintaining expensive climate controlled server environments.

The technology is nowhere near ready for integration, unfortunately. IBM projects a 10 to 15 year development for the system. Eventually, rather than the racks full of dual and multi-core processors sported by supercomputers like Blue Gene/L, we could see a computer many times more powerful housed in something the size of a current mid-tower ATX case.

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By nerdye on 12/10/2007 11:07:18 AM , Rating: 2
I have been waiting for this type of announcement involving optics used as interconnects to cpu's and all hardware for a long time. Thank you IBM!

RE: finally!
By initialised on 12/10/2007 11:45:53 AM , Rating: 2
This idea is not new, just on the threshold of being necessary. I looked into doing clocking with optics for my degree project in 2001. I think it's great for the system bus but not good enough for intra chip communications. The main limitation is the size of the laser and receiver.

Just think how the current PC layout limitations can be stripped away if they are all on a single optical bus.

"I'm an Internet expert too. It's all right to wire the industrial zone only, but there are many problems if other regions of the North are wired." -- North Korean Supreme Commander Kim Jong-il
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