HP to utilise silicon photonics on chip
By harnessing its expertise in nanoimprint lithography to fashion low-cost, high-speed silicon photonic devices, HP said it hopes to seed the fledgling community of optical interconnect component makers. Rather than doing it all, HP is seeking partners with other silicon photonic pioneers in hopes of developing its first optical interconnect technology in products by 2009.
"I hope that by next year's Photonic Interconnect Forum, we will be able to give product demos instead of just research results," said HP fellow and CTO Terry Morris. "Our business strategy is to pull partners along and build a community that benefits from the intellectual property at HP Labs—a community that provides the ecosystem to enable the delivery of photonic interconnects in volume."
HP described its laboratory demonstrations of the components needed for creating optical interconnects that handle communication among systems and boards, including two versions of an optical interconnect—a free-space bus (that beams light through air) and a photonic-fibre bus.
Its free-space optical connection provided a 240Gbps optical connection that beamed information through the air between boards. Researcher also described a MEMS micro-lens scanner fabricated from silicon-on-insulator that focuses between-board lasers.
"We have characterised just what we need to make photonic connections work, making very detailed measurements of vibration and board offset and all the other parameters that needed to be characterised in order to quantify the operating environment for photonic interconnects," said Morris.
HP Labs also showed how its optical bus could harness nanoimprint lithography to fashion cheap plastic waveguides, micro-lenses and beamsplitters. Its first demonstration was of a 10bit-wide optical data bus that used just 1mW of laser power to interconnect eight different modules at 10Gbps/channel for an aggregate bandwidth of over 250Gbps.
"What we are working towards now are novel optical connections, such as board-to-board connections using a photonic bus that enables us to replace an 80W chip that performs the electronic switching function today with a moulded piece of plastic," said Morris.
Most photonic interconnects use vertical cavity surface-emitting lasers, but HP Labs also showed inexpensive methods of eliminating the need for expensive gallium arsenide chips, using plasmonic LEDs that could cut costs, and a silicon ring resonator that it hopes to fashion with imprint lithography.
"HP Labs has already demonstrated one of the world's smallest and lowest power silicon ring resonators. Now we want to show how to do it with nanoimprint lithography because a dense pattern that takes 60 hours to create with e-beam lithography could take only 30 minutes for nanoimprint lithography," Morris claimed.
Ready for mass market
HP contends that its photonic interconnects are poised for commercialisation, which will begin immediately along with business partners. In addition to HP's university partners, over a dozen companies attended the HP forum, including Avago, Corning, Intel and Lightwire.
HP's motivation for hosting the Photonic Interconnect Forum was to start a full-fledged commercialisation effort designed to bring optical interconnects to market sooner rather than later.
"We don't want to start with supercomputers and hope that it trickles down," said Morris. "With photonic interconnects, we want to start with volumes from the outset."
Instead of using telecommunications-type photonics—which is designed for 300m ranges—HP said it wants to craft a family of low-power signalling technologies that use silicon nanoimprint lithography to fashion low-cost alternatives for optical communications.
The goal is to develop "the infrastructure to get photonic interconnects to market," said Morris. "We already have photonic waveguides that can operate at up to terahertz ranges. Now we want to make sure that our solutions work in real computing environments," said Morris.
"We want to expand our photonics business to include all communications in the range of 100 nanometres on a chip all the way up to 100m between systems," the HP executive added. "In the near term we want to connect boards and blades with photonic interconnects. In the long-term we want to build on-chip photonic connections which we think will break the core-to-memory bottleneck."
Photonic interconnects have been touted as not only improving performance and solving bandwidth problems, but also operating at much lower power than conventional electrical switches, according to HP.
Cheap photonic interconnects will also usher in new computing architectures that utilised dedicated optical connections rather than sharing all the interconnections through a bus or network.
"Instead of going through a switch and out onto a congested bus then back through the switch, we plan on adding inexpensive direct connections that add a dimension of connectivity not possible today," said Morris. "For instance, we could add photonic connections between blades for true 3D meshes and toroids, while remaining within the confines of existing board infrastructures."
HP claims to be working on configuration and packaging problems in hopes of getting photonic interconnect products ready by next year. Its chief competitor in the field is IBM Corp.
"We are currently solving some fundamental electrical problems, like physical adjacency problems, interconnect power in switch hierarchies and pin-count versus core-count on our packages," said Morris.
- R. Colin Johnson
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