TECHNOLOGY FOR CHANGE

IBM Preps Optics to Replace Copper Interconnects

R. Colin Johnson | Date: 03-11-10 | Comments

Recently perfected optical interconnection technologies will obsolete copper traces for routing electronic signals around on printed circuit boards (PCBs) and even between cores inside microchips, according to IBM, which plans to commercialize on-chip optics over the next few years.

Optical fibers already carry the fastest communications signals over the Internet and between servers and supercomputers at high-performance data centers. By encoding electronic communications in the language of light, the higher frequencies and wider bandwidth of optical signals not only increases performance, but obsoletes heavy, bulky copper-based interconnects in favor of small, lightweight optical fibers.

Future silicon CMOS multicore microprocessor chips will use optical nanophotonics on its top layer to interconnect memory and processor cores.

Unfortunately, all the optical interconnection technologies today rely on expensive, discrete indium- and gallium arsenide-based transceivers that cannot be integrated onto the same silicon-based chips as processor cores. Consequently, optical fiber interconnects are only used between computer systems today. In the future, however, IBM Research (Yorktown Heights, N.Y.) and many other semiconductor development organizations worldwide are pursuing silicon-based optical communications technologies that can be integrated directly onto modern multicore processors.

Over the last decade, IBM in particular has begun announcing breakthrough optical devices that can be integrated on standard silicon multicore processor chips using complementary metal oxide semiconductors (CMOS). But to enable optical communications between and among multicore processors required developing a whole ecosystem of silicon-based optical devices that IBM dubs its nanophotonic toolkit.

Each year, IBM announces a few more elements in its nanophotonic toolkit, including on-chip silicon-laser resonators, modulators, waveguides and switches. Plus, it has demonstrated a complete chip-to-chip optical bus.

Now IBM claims it has crafted the final tool in its nanophotonics kit -- a tiny germanium optical receiver called an avalanche photodetector -- that will enable it to realize the dream of integrated CMOS optical interconnects. The new 40G bps photodetector can be integrated on the edge of processors to receive optical signals sent between chips instead of using copper traces on printed circuit boards. And eventually, it will be integrated on the top layer of the microprocessor itself to facilitate lightning-fast communications between cores on the same chip, thus eliminating the need for copper wires inside and outside future electronic devices.

Optical signals are not only faster, but can be encoded onto different colors of light for multiplexed communications that are light-years ahead of even the highest speeds attainable with copper wires. And for portable devices, on-chip and between-chip optical interconnects promise to cut both the power consumed -- thereby increasing battery life -- as well as the weight of electronics. By eliminating the copper traces on printed circuit boards and the copper wires inside the chips themselves, a major reduction can be made in the weight of mobile devices today.