PORTLAND, Ore. IBM Corp. described what it claims is the world's first optically-connected circuit board on Thursday (Feb. 28) at the Optical Fiber Communication Conference in San Diego.
Researchers at IBM's Thomas J. Watson Research Center (Yorktown Heights, N.Y.) said the 160-Gbits/sec optical interconnect was lithographically patterned atop an otherwise conventional pc-board. Dense low-power CMOS transceivers were used to convert normal electrical signals into light.
"This is the first real demonstration of an optical printed circuit board interconnect operating at very high data rates and in a very compact format," said IBM researcher Clint Schow. "In the future, optical busses like ours could interconnect two processors or a processor to its memory."
|IBM demonstrated 32-channel optical interconnects for printed circuit boards.|
IBM also claims its technology is "green," noting that it would require only about 100 watts to transmit 5,000 high definition video streams at eight terabits/sec--sufficient bandwidth for even the largest data centers. IBM also claims its optical interconnects consume 100 times less power than electrical interconnects used in current data centers, and 10 times less than conventional optical fiber interconnects. The researchers estimate that commercial versions of its optical interconnects will be available within two years.
IBM described two optical interconnects at the conference: one used transceivers to achieve 24 bidirectional channels; the other running at 12.5 Gbits/sec. The second version used a compact, custom IBM transceiver that packed 16 bidirectional channels each running at 10 Gbits/sec.
Last year, IBM demonstrated an optical transceiver chip which was capable of transmitting five high-definition video feeds down each channel. This week, IBM demonstrated a complete implementation utilizing its transceiver design integrated with an optical bus on a pc-board.
IBM first fabricated a complete conventional board, then added polymer waveguides to its top surface using the same type of lithography used to deposit metal traces on chips. To demonstrate its own custom transceivers, IBM spaced two modules 15 centimeters apart and connected them through 32 waveguides, yielding the transceivers' 16 bidirectional channels. Finally, they were connected at 10-Gbits/sec.
"Our polymer waveguides are 35-microns-wide and tall, with 27 microns between them," said IBM researcher Fuad Doany. "That's about twice the density of conventional optical fibers."
For its demonstration board, the polymer waveguides were laid out in straight lines between the two modules. But IBM researchers also demonstrated that the waveguides can be smoothly curved for easier routing of optical signals around a board.
"When connecting chips on a board with our waveguides, they can tolerate bends with a radius of about 15 millimeters," said Doany.
IBM's transceivers utilized low-cost arrays of 850-nm wavelength vertical-cavity surface-emitting lasers, which were directly modulated by the electrical signals from the interconnected chips.
In a separate project, IBM has also demonstrated silicon waveguides modulated by a Mach-Zehnder interferometer--a CMOS process that is also used by Lightwire Inc. (Allentown, Pa.) and Luxtera Inc. (Carlsbad, Calif.)
Funding for the IBM project was provided by the Defense Advanced Research Projects Agency.