Sandia National Laboratories Albuquerque, New Mex.

3D Silicon Photonic Lattice

It's no secret that today's electronics move much more slowly than the speed of light. But what if you could use optical technology to quicken the speed of all kinds of electronic communications? In fact, it's already happening in research labs around the country. And this year, researchers Jim Fleming and Shawn Lin at Sandia National Laboratories, in collaboration with several scientists at other U.S. institutions, introduced an important breakthrough in the field known as called photonics. Their technology, a three-dimensional silicon photonic lattice or crystal, derives from the clever integration of photonics expertise and silicon processing. Photonic devices -- including lasers, light-emitting diodes, high-performance mirrors, optical filters, and wave guides -- are at the heart of the emerging global communications infrastructure. Until now, such devices could only be made effectively from compound semiconductors like gallium arsenide, which have not developed at a pace as rapid as that of silicon. Because of the slower improvement rate, compounds carry a higher price tag than their silicon counterparts, and the high cost -- along with performance issues -- has been one of the obstacles inhibiting the widespread commercial use of photonics in communications markets. Silicon has presented problems for photonics researchers. "Silicon is a great semiconductor, but it doesn't emit light the way other semiconductors do," explains Pierre Villeneuve, a research scientist at Massachusetts Institute of Technology. Fleming and his colleagues were determined to find a way to use silicon in photonics anyway. "Our understanding of silicon is unequaled because of the massive infrastructure that has evolved around its use in the microelectronics industry. We have specialized tools, materials, and processes; large area substrates; and a vast body of knowledge to draw from," he explains. Sandia Laboratories' breakthrough is in creating a microscopic lattice or crystal that interacts with light in a way that is analogous to the interaction between electrons and a semiconductor; thus, the new technology enables the fabrication of a 3-D silicon photonic lattice, which Sandia has used to produce infrared mirrors and filters. Now, Sandia plans to license the technology to partners involved in optical communications, scientific instruments, and military operations. The most immediate applications include thermal emission control, a market estimated at $500 million, as well as target acquisition, tracking and pointing, and remote sensing of chemical and biological agents. The more significant effect, however, will be in optical communications, in applications where optical fibers are used to interconnect computer networks. "In making switches for the communications market, you need to redirect data and to be able to turn it on and off. Photonic crystals are a very appealing media to use in accomplishing this," says Villeneuve. In this application, data is stored on photons or packets of light and distributed across a network. Once performance issues are addressed, the packets of light should move much more quickly than conventionally switched packets of data. Fleming indicates that the 3-D silicon photonic lattice will most likely be used specifically for a technique called Wavelength Division Multiplexing (WDM), a segment of the telecommunications market that's expected to be worth $4 billion by 2000. (WDM technologies essentially broadcast data from various sources to numerous recipients. Each source has a laser with a specified frequency and each recipient tunes a receiver to that same frequency.) Fleming and Lin are taking advantage of the maturity of silicon processing and applying it to photonics. Meanwhile, other research laboratories continue to look for new approaches and applications for photonic devices, as well.

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