Data in a flash

One of these new interconnects, called Light Peak, has been developed by Intel. It is being used to give ordinary PCs the ability to connect with other devices using high-speed optical cables at ten gigabits per second—20 times faster than a standard USB cable. This means the cable could drive a high-definition display or transfer a movie in seconds. Light Peak, predicts Mario Paniccia, the head of Intel’s photonics lab, will make optical connections as pervasive as wireless ones—and drive demand for more powerful processors, which explains Intel’s interest.

Intel did not have to invent anything new, but it did have to work out how to make small, cheap versions of the converters that turn electrical signals into light and vice versa. Having developed a simplified, low-cost chip to do the job, Intel also devised ways to assemble and test the components quickly, and signed up a group of suppliers to churn them out by the million, starting next year.

Hewlett-Packard’s concern is keeping its servers competitive: their cabling is getting bulkier, and data centres are becoming much harder to cool and increasingly energy hungry. So it is developing an optical replacement for the interconnects in server “racks”. Instead of optical fibre, HP is using waveguides—small strips of plastic with grooves on their highly reflective metallic walls. Again, using this technology to transmit light is not a new thing, but HP’s researchers have managed to cut costs by making waveguides with an injection-moulding system similar to that used to mass-produce CDs.

Over at IBM, researchers are using optical interconnects to make supercomputers run faster. To speed up the flow of data, electrons need to be turned into photons “as close as possible to where the signal is processed”, explains Bert Offrein of IBM Research. For this reason, it is mounting fibre-optic cables straight onto the chips that direct the traffic between a supercomputer’s multiple processors.

The idea of using similar optical interconnects between a computer’s various components is, based on existing technology, not something that is about to appear in humble home or office PCs any time soon. It is hard to make such components small and cheap enough to compete with copper wiring. But one technology that does show promise in making such connections is called “silicon photonics”. It uses similar methods to those employed to manufacture processors and other types of integrated circuits.

Conveniently, silicon is not a bad material for making optical devices. Researchers at HP Labs recently managed to etch a pattern into a flat piece of silicon so that it could focus light “like a spoon”, says Raymond Beausoleil of HP Labs. This effect, he says, could be used to improve lasers and replace expensive lenses in DVD players and other consumer products.

For its part, IBM has used silicon to develop a fast and extremely thin photodetector to convert optical signals into electrical ones. And Intel has come up with an entire kit of tiny optical devices made of silicon, which it hopes one day to combine on optical chips, such as waveguides and lasers. But one vital building block is missing from Intel’s kit: an optical equivalent of the transistors that perform the logical operations at the heart of a computer.

This missing bit does not surprise David Miller of the Photonics Research Centre at Stanford University. Optical transistors, he says, will have a hard time competing with electrical ones, not least because there is no agreement over the best way to build them. Various techniques for making optical transistors regularly appear in laboratories. But using light to process information is tricky, requires exotic materials and lasers that demand more power than conventional transistors. Moreover, miniaturisation is not straightforward, not least because lasers cannot be made as small as transistors. So mass-produced optical processors remain far off. But at least the other bits are on the way.