Computers That Use Light Instead Of Electricity?
MIT researchers have demonstrated the first laser built from germanium that can produce wavelengths of light useful for optical communication.
It's also the first germanium laser to operate at room temperature. Unlike the materials typically used in lasers, germanium is easy to incorporate into existing processes for manufacturing silicon chips.
So the result could prove an important step toward computers that move data - and maybe even perform calculations - using light instead of electricity. But more fundamentally, the researchers have shown that, contrary to prior belief, a class of materials called indirect-band-gap semiconductors can yield practical lasers.
As chips' computational capacity increases, they need higher-bandwidth connections to send data to memory. But conventional electrical connections will soon become impractical, because they'll require too much power to transport data at ever higher rates. Transmitting data with lasers - devices that concentrate light into a narrow, powerful beam - could be much more power-efficient, but it requires a cheap way to integrate optical and electronic components on silicon chips.
Chip assembly is a painstaking process in which layers of different materials are deposited on a wafer of silicon, and patterns are etched into them. Inserting a new material into this process is difficult: it has to be able to chemically bond to the layers above and below it, and depositing it must be possible at the temperatures and in the chemical environments suitable to the other materials.
The materials used in today's lasers, such as gallium arsenide, are "all tough fits," says Tremont Miao, a marketing director at Massachusetts-based Analog Devices Semiconductor. "They're all challenging integrations." As a consequence, the lasers have to be constructed separately and then grafted onto the chips, which is more expensive and time-consuming than building them directly on silicon would be. Moreover, gallium arsenide is much more expensive than silicon in the first place.
Integrating germanium into the manufacturing process, however, is something that almost all major chip manufacturers have already begun to do, since the addition of germanium increases the speed of silicon chips. "We and lots of other people know how to do that," Miao says.
"MIT researchers have demonstrated the first laser built from germanium that can produce wavelengths of light useful for optical communication. (Credit: Graphic by Christine Daniloff)"
Source: Massachusetts Institute of Technology
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