IBM silicon nanophotonics speeds servers with 25Gbps light

Dec 10, 2012

IBM has developed a light-based data transfer system delivering more than 25Gbps per channel, opening the door to chip-dense slabs of processing power that could speed up server performance, the internet, and more. The company's research into silicon integrated nanophotonics addresses concerns that interconnects between increasingly powerful computers, such as mainframe servers, are unable to keep up with the speeds of the computers themselves. Instead of copper or even optical cables, IBM envisages on-chip optical routing, where light blasts data between dense, multi-layer computing hubs.

"This future 3D-integated chip consists of several layers connected with each other with very dense and small pitch interlayer vias. The lower layer is a processor itself with many hundreds of individual cores. Memory layer (or layers) are bonded on top to provide fast access to local caches. On top of the stack is the Photonic layer with many thousands of individual optical devices (modulators, detectors, switches) as well as analogue electrical circuits (amplifiers, drivers, latches, etc.). The key role of a photonic layer is not only to provide point-to-point broad bandwidth optical link between different cores and/or the off-chip traffic, but also to route this traffic with an array of nanophotonic switches. Hence it is named Intra-chip optical network (ICON)" IBM

Optical interconnects are increasingly being used to link different server nodes, but by bringing the individual nodes into a single stack the delays involved in communication could be pared back even further. Off-chip optical communications would also be supported, to link the data-rich hubs together.

Although the photonics system would be considerably faster than existing links - it supports multiplexing, joining multiple 25Gbps+ connections into one cable thanks to light wavelength splitting - IBM says it would also be cheaper thanks to straightforward manufacturing integration:

"By adding a few processing modules into a high-performance 90nm CMOS fabrication line, a variety of silicon nanophotonics components such as wavelength division multiplexers (WDM), modulators, and detectors are integrated side-by-side with a CMOS electrical circuitry. As a result, single-chip optical communications transceivers can be manufactured in a conventional semiconductor foundry, providing significant cost reduction over traditional approaches" IBM

Technologies like the co-developed Thunderbolt from Intel and Apple have promised affordable light-based computing connections, but so far rely on more traditional copper-based links with optical versions further down the line. IBM says its system is "primed for commercial development" though warns it may take a few years before products could actually go on sale.

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