'Invisibility cloak' is possible

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Melbourne: For the first time ever, researchers have demonstrated a reversal of the optical Doppler effect, an advance that could lead to the development of ‘invisibility cloak’ technology.

The Doppler effect describes the change in frequency of waves whenever there is a relative movement between an observer and a wave’s source.

When an object and an observer move closer together, light frequency increase from red wavelengths to blue. When the light source moves further away, light frequency decreases from blue to red.

The researchers from Swinburne University in Melbourne and their collaborators from the University of Shanghai for Science and Technology, have demonstrated the reversal of this effect, which does not occur naturally.

That is, when an object and a light wave detector moved closer together, they were able to decrease the light frequency from blue wavelengths to red ones, and vice versa.

The researchers achieved this effect by creating an artificial nanostructured crystal—known as a ‘photonic crystal’ out of silicon.

"In our super prism the dispersion of light was twice the magnitude of a standard Newton prism," ABC Science quoted Min Gu, Director of Swinburne's Centre for Micro-Photonics, as saying.

"This large angle makes the prism's refractive index (a property that determines how fast light travels through it) change to negative.

"By creating this artificial material, with a negative refractive index, we were able to reverse this natural phenomenon," said Gu.

The researchers also said that being able to reverse the Doppler effect is a promising sign for the future development of technology such as invisibility cloaks, which effectively bend light around an object.

The findings have been published in the Nature Photonics journal.