Light switches that could boost fibreoptic efficiency

Glass panes capable of steering light beams could be used to improve the efficiency of telecommunications networks, physicists in the US have claimed.

Researchers at Harvard University are using liquid crystal droplets to create glass panes capable of switching between transparent and diffracting states as an electric field is applied. When transparent, a laser beam passes straight through the glass, but when diffracting, the pane splits the beam.

The technique could be used to improve the efficiency of fibreoptic networks, in which information is transported along different wavelengths of light, said David Weitz, professor of applied physics at Harvard University and lead researcher on the project.

‘This could form the basis of a switch that controls the direction of light, and could conceivably be used in fibreoptic networks as a switch between different fibres. The light could exit one fibre and be routed to another – in fact, several routes could be selected.’

Liquid crystal droplets are already used in advanced window panes to change the glass from transparent to opaque at the flick of a switch. But these panes contain a random distribution of drops, meaning they simply scatter light in all directions.

In contrast, the Harvard team, with funding from NASA, has developed a technique to produce equal-sized droplets of liquid crystal, each about a dozen microns across, which are packed together on the glass plate in a honeycomb pattern. As a result the droplets diffract light rather than simply scattering it, said Weitz. ‘This is what allows us to control the direction of the beam.’

An electric field steers the rod-shaped molecules in each droplet, controlling how they guide the rays of light passing through them.

The liquid crystal panes could also be used in displays or in astronomy, combining beams of light from multiple telescopes to magnify the light from distant planets.

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