Fiber optic cables used to be simple: just long, thin glass strands for light to travel down. But now chemists have discovered a method to grow thin wires of metal inside them. This could revolutionize optical electronics by making all-in-one devices within a single optical fiber.
Trans-Atlantic telephone cables and the internet both rely on optical fibers to transmit information as light. The fibers contain light by using two types of glass: an inner core mixed with germanium oxide, and an outer layer of pure silica glass. Light can't stray from the core because it will reflect off the inner wall of the outer layer and bounce back in. But that's not all. In 1996, researchers discovered that by adding long, tiny tunnels--called holes or pores--that run the length of the fiber, they could modify the properties of the light. An engineer, for instance, could send a pulse of blue light through a holey fiber, and it would emerge as white light. The trick seriously upped the bandwidth of optical fibers.
Holey fibers have yet more potential; the pores can be lined with useful materials, such as semiconductors. At first, researchers assumed that it would be difficult to coat the 1-micron-wide holes without clogging them. But John Badding, a chemist at Pennsylvania State University in University Park, and colleagues at the University of Southampton in the U.K. describe success in the 17 March issue of Science.
The team baked holey optical fibers in a 500 degree Celsius furnace while forcing a hot gas of germanium hydride through the pores. The high temperature and pressure allowed solid germanium to crystallize along the walls of the pores. These germanium wires still had a tiny central hole just a few tens of nanometers wide running through their middles that allowed light to pass. But Badding and colleagues could arrange the wires in such a way that light passing through generated a current. They have already built a simple transistor within a fiber using the technique, and they predict that eventually optical fibers will contain the whole host of basic electronic devices.
John Kouvetakis, a solid-state chemist at Arizona State University in Tempe, agrees. The semiconductor wires within the fiber "are well-organized and can be rearranged to make useful things," Kouvetakis predicts. "It's a neat experiment," he says.
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