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Intel ventures into optical interconnects

Posted: 16 Feb 2009 ?? ?Print Version ?Bookmark and Share

Keywords:optical interconnect? microprocessor? computing tera-scale?

Intel Corp. is looking into optical interconnects with an eye toward replacing chip-to-chip electrical interconnects to overcome looming bandwidth issues as microprocessors with an increasing number of cores usher in the era of tera-scale computing.

Ian Young, an Intel Fellow and director of Intel's advanced circuits and technology integration project, presented a paper at the IEEE's International Solid State Circuits Conference (ISSCC) Feb. 11 describing progress in integrating the waveguides, detectors and modulators needed for integrating photonic interconnects directly onto CMOS chips.

Young described the performance of an 8-channel, 90nm device that has demonstrated transmission and reception speed of up to 10Gbit/s. The company's longer-term goal is to make optical components that can achieve higher bandwidth of between 100GBps to 1TBps, Young said.

Sending information via photons as opposed to electrons offers inherent advantages in terms of higher speed and lower power consumption. But monolithic integration of the required photonic and electro-optic components within CMOS chips presents a host of challenges.

In his presentation to the ISSCC Monday, Mark Bohr, Intel senior Fellow and director of process architecture and integration, described interconnect as one of the five major challenges facing IC scaling to the 32nm node and beyond. Bohr said optical interconnects could be the solution "if technologies can be developed that cost effectively integrate photonics with silicon logic."

A recent panel of experts at the Photonics West acknowledged that the computer industry wants optical interconnects in its future multicore processors, but agreed that there is no clear light source to drive on-chip optics and said the technology needs to get to significantly lower heat, power and cost to be viable.

Light has been used to transmit data for decades. In telecommunications, fiber optic systems have been in use since the 1970s. Photonic technology is also used in computer networks and is increasingly displacing electronic transmission for shorter and shorter distance communications.

Many-processor system
For Intel's prototype chip, a microprocessor, the photonics are placed on top of the CMOS die, which does not compromise the performance of the device's transistors, Young said. "Because we are on top of the die, it's easy to get light on and off the chip," Young said.

The transition to many-core microprocessor architectures is expected to drive increased chip-to-chip I/O bandwidth demands at processor/memory interfaces and in multi-processor systems, according to Young's paper. Future architectures will require bandwidths of 200GBps to 1TBps, the paper states. Electrical interconnects would require increases in circuit complexity and costlier materials in order to meet this requirement, according to the paper.

"Optical interconnect with its terahertz bandwidth, low loss, and low cross-talk has been proposed to replace electrical interconnect between chips," the paper states.

Wavelength-division multiplexing is used in the research for additional bandwidth enhancement, according to the paper.

The Intel paper describes a longer-term goal of creating a microprocessor with integrated on-die, single-mode silicon nitride optical waveguides, silicon nitride waveguide coupled metal-semiconductor-metal germanium detectors and electro-optical polymer based ring-resonator modulators. The company hopes to achieve optical components that can reach very high bandwidth and energy efficiency for an optical I/O link that is compatible with CMOS processing and can be fabricated in the same process flow without sacrificing transistor performance, according to the paper.

Eventually, Young said, Intel sees photonics technology for use in on-chip, core-to-core as well as off-chip, core-to-memory interconnects.

"Optical interconnect will enable CMOS transistor scaling to continue I/O bandwidth," Young said.

CPU optical interconnect will first be introduced for the package-to-package optical I/O, initially with a "hybrid" single package technology, according to Yong's paper. "If the challenges of fully integrated optical elements in the CMOS process can be overcome, then monolithically integrated optical components will provide the path to the TB/s I/O data rates with the required energy efficiency near 1pJ/b," the paper concludes.

The full paper, "Optical I/O Technology for Tera-Scale Computing," can be read on TechOnline.

- Dylan McGrath
EE Times

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