TINY liquid lenses that set solid in a flash of light could slash the cost of making 鈥渙ptical chips鈥�. Scientists at Lucent Technologies鈥� Bell Labs in New Jersey have developed a technique for solidifying a liquid lens as soon as it is the right shape.
Optical chips fire light around fibre-optic 鈥渃ircuits鈥� to process data. At the moment their components have to be lined up with the optical fibres using a fiddly miniature robot hand called a micromanipulator.
The trouble is that unless the pieces are aligned to within a micrometre, light gets lost at junctions, ruining the signal. So makers nudge the components until readings show they have a good transfer of light, and only then can they weld the pieces onto an underlying board.
Advertisement
But welding usually slightly upsets the alignment of the optical components, so the pieces have to be gently hammered to put them back in line. 鈥淭his takes over 20 minutes per connection and means optical chips cost a hundred times as much as they should,鈥� says Tom Krupenkin at Bell Labs.
Krupenkin decided to see whether an intervening lens would allow the alignment to be less precise. Once the components had been welded roughly in line, he inserted a drop of saltwater between them.
Using a transparent electrode underneath the droplet, he built up a charge difference between the water and a nearby insulating surface. The resulting electrostatic force between the water and the insulator flattened the droplet, and by adjusting the charge, the researchers could control the shape of the lens precisely.
This focused the light across the junction and exactly compensated for any minor errors in alignment. 鈥淟iquids are nice because you can change their form easily and symmetrically,鈥� he says.
Although people have made liquid lenses before (New Scientist, 22 May 1999, p 6), they鈥檙e too unstable to be practical, since they can bulge out of shape if turned upside down or shaken.
So Krupenkin and his colleague Shu Yang tried replacing the saltwater lens with a droplet of transparent glue. Adding a trace of salt to the glue made the droplet conduct electricity well enough for them to control its shape with the electrode. As soon as the droplet was the right shape, the scientists set it solid by exposing it to ultraviolet light. This turned it into a plastic lens with the same size, shape and optical properties as the liquid drop.
John Dutcher, who works on polymers at the University of Guelph in Ontario, reckons Krupenkin鈥檚 method is very flexible. He says the technique could also make it easier to produce optical displays such as flat screens, where manufacturers need to have very precise control over the dimensions and optical properties of a material. 鈥淵ou could have a whole array of these lenses,鈥� he says.
