Portland, Ore. -- With optical processing migrating from exotic gallium arsenide devices to inexpensive silicon, Intel Corp. showed a research chip earlier this year that could do the world's first Raman lasing in a silicon waveguide. An all-silicon device, it had dynamically tunable wavelengths but was not very scalable, requiring an off-chip laser as an optical pump. Now, Intel is describing a scalable on-chip indium phosphide laser bonded to an all-silicon waveguide. Such an on-chip laser could supply the missing link between optics and electronics by performing both functions on the same photonic chips.
Intel discussed the latest milestone on the long and crooked road to silicon photonic chips at last week's International Semiconductor Laser Conference in Hawaii. There, Mario Paniccia, director of Intel's Photonics Technology Lab, was scheduled to announce a collaboration with the University of California at Santa Barbara (UCSB) in which "we have uniquely combined the best of both [optical and electronic] worlds. Our solution, I believe, is manufacturable, but it is still a research breakthrough," he said.
Paniccia estimated that five to 10 years of development remained before wafer-scale indium phosphide lasers could provide optical interconnection signals for hybrid chips using indium phosphide lasers bonded atop silicon chips.
"We still have quite a bit of work to get it to the next level of development and then on to manufacturing, but we are excited because we have the ability to put hundreds of indium phosphide lasers on silicon chips all across a wafer in one bonding step with no alignment [problems]."
Indium phosphide is an even better light emitter than gallium arsenide, but its crystalline lattice is grossly mismatched to that of silicon. Failure of the usual epitaxial methods to grow indium compounds on top of a silicon wafer has foiled previous attempts to marry the two technologies. UCSB's innovation was to sidestep the problem by bonding indium phosphide wafers to silicon wafers. The UCSB/ Intel approach does not even try to solve the crystalline-lattice mismatch, but instead uses a low-temperature (300°C) plasma deposition step to create a 25-atom "glass-glue" to bond a flipped InP wafer to a silicon wafer.
"This could be the next big thing in optical communications: bonding high-performance indium phosphide lasers to CMOS chips," said semiconductor analyst Stephan Ohr at Gartner Group (San Jose, Calif.). "Intel is in step with companies specializing in optical chips--they are already researching methods of making such hybrid lasers for next-generation optical interconnects."
So far, getting Intel's Raman waveguide to lase has required an off-chip laser to pump it, but the new on-chip indium phosphide laser could provide that pumping action.